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MG MGB Technical - More Starting Problems
|Well, I thought I was ready for spring. '73BGT, HIF4 carbs. Was having hesitation and "spitting" problems while running - that turned out to be a lean mixture. Went for a very nice spring cruise, and the following day it would not start. Fuel to the carbs was fine. Suspected something stuck after the winter time out. Tried some carb cleaner, and it started, but reluctantly with a backfire. After starting, it ran very well - good power on hills, perfect idling, etc. After an overnight in the garage - no start again.|
Finally, turning the ignition key resulted in nothing - to starter click, no ignition light, etc. Took the battery to a shop for testing - tested as fully charged, with plenty of cranking amps.
Now I am at a loss - ignition switch? Starter solenoid?
Any ideas most welcome. Especially frustrating after running so smoothly.
|Could be starter relay, or indeed the ignition switch itself.|
|If you get no response from the starter when you turn the key to start position and you have lights and accessories, you have a bad ignition switch.|
let us know what your outcome is
|1 Check a bad ground connection to the battery. |
2 Check a bad positive connection to the starter
|Gary's is the first check, fuel gauge not rising also points to ignition switch or its connections. If no lights either then could be either battery connection and that means connectors to posts, cables to connectors as well as earth cable to body. Or battery cable and or browns and the solenoid.|
If you do have lights then the ignition warning light and cranking are dependent on their being an engine earth, but usually accelerator, choke, heater cables etc. give a good enough earth for the warning light at least.
|Thanks all. Hoping to spend some time with those checks today. Will post any progress.|
|Well, re-checked all batter connections again. The positive wire clamp broke when tightening. Not sure if it was cracked before, or if that could have caused any of the earlier symptoms. Changed both clamps, now all is clean and tight.|
Turned the ignition switch to on position - fuel pump actuated and have all lights. Turned to start position - now have a good ignition light, and car attempts to start (without carb cleaner), but backfires and then stops firing. Fuel pump and lights continue, but it will not fire. Wait a short time, and the same thing - backfire then no fire, even though starter continues to turn the engine over.
Back to the diagnostics. Will update if/when I have any luck.
|You are cranking, that's good. backfiring is indicitive of ignition problems. If you have a point/condenser system, recheck point gap. If it still exists, try a different condenser.|
Neighbor had a similar issue with an old Chysler slant 6 which turned out to be the secondary coil wire was no good. After that he was good to go.
|Are you sure plug lead order is correct? 1 3 4 2 counting anti-clockwise, and if you have had all the leads off you may need to recheck where the rotor is pointing when No.1 cylinder is at TDC on it's compression stroke.|
|Another thought - could the distributor clamp be loose allowing the timing to slip? As Gary said, backfiring often points (oh, a pun!) to an ignition problem.|
|Re-checked point gap, plug lead order, and distributor clamp. All fine.|
Attempts to start on carb cleaner - without backfire now, but stops firing as soon as the cleaner is burned.
I am leaning away from ignition as the problem - because if/when I get it started, it runs very well - with dwell, idle, etc. all stable and on spec.
I guess that means I have to get back on the search for a fuel blockage. Every time I check the inlet to the carbs, the fuel seems be getting that far, but ...
I can't believe both carbs would block the flow at the same time.
|Ok. So if you continue to spray carb cleaner into the carbs, the engine will run in that mode ONLY ??!! If this is true, then you have a fuel supply issue. Check|
|My post was cut short|
Check fuel flow by disconnecting fuel line from the carbs and direct the line into a bottle. Turn the key on and observe the fuel stream. If it is weak, disconnect the fuel line from the fuel filter and repeat the above process. Hopefully there will be a marked difference. If the flow is still weak after disconnecting the filter, you will have to work your way back through the fuel supply system.
If the fuel flow is strong throughout, you may have to get into the carburetors.
The carb cleaner does seem to be the only thing firing. While I have used the bottle-check in the past, and then had good running, it is possible that another blockage has occurred, as you said. Guess that's my next check. Hope to find something without digging into the carbs.
The gas here is not the greatest, and the ethanol doesn't help these cars.
I will post any results/updates,
|I meant to add: Is there a way to bypass the anti run-on valve to make sure that is not starving the carbs when the ignition is on? I do hear a click when I turn the switch on, and another click when off and oil pressure drops. That should indicate a working valve, but might be worth a check. I have replaced the oil pressure switch with the proper one from Moss, and that seems to be working.|
|The valve shouldn't click when the ignition is turned on.|
It is only supposed to operate when you switch off a running engine, and you are unlikely to hear it then. That will stop the engine in any event, and as the oil pressure dies away the valve should click as it releases.
If you have replaced the oil pressure switch you need to check you do have the right one by testing it and not take their word for it. Unlike a conventional oil pressure switch that is closed when there is no pressure, the anti-runon switch only closes when it has pressure, i.e. it shouldn't be closed with the engine stopped.
However the first thing is to do is remove the hoses from the carb overflow ports and try again. If it now runs OK then there is a problem with the anti-runon valve plumbing. So replace the hoses on the carb overflow ports, check you still have the problem, then remove one of the wires from the valve. If it doesn't happen now there is a problem with the valve or its wiring including the oil switch. If it still happens then it is some other problem with the emissions plumbing.
If the engine still doesn't start with the overflow port hoses removed then there is a problem with fuel supply. However it could be a massive vacuum leak somewhere, the Welch plugs in the inlet manifold have been known to blow out.
Alternatively if you blow in the overflow ports while looking at the jet, you should see fuel bubbling up. If not either there is no fuel in the float chambers, or it isn't getting up the jets. With HIF carbs the rear carb is fed from the front one, so a blockage in the front carb could well affect both carbs.
Great info, as always. Interesting - I do hear a distinct click when the ignition goes on, and another after it is turned off and oil pressure drops. I am pretty sure I checked the oil pressure switch when I received it, because I had been given two of the wrong type earlier.
I will go through your procedure and update results.
|Well, progress - I hope.|
Checked the oil pressure switch, and it is the correct on (normally open with no oil pressure).
Removed hoses from the carb overflow ports - blew into each, and there were bubbles in each carb. With hoses removed, the car started immediately and continued to run fine.
Replaced the hoses and tried again - started right up and ran fine (with ARO valve wires connected).
I should note that now I do not hear a click when the ignition switch is turned on.
So, while I am a little confused about what could have been "fixed" by removing and then replacing the overflow hoses, I am at least seeing major progress.
I will now wait a while to try again with everything hooked up - to see if the problem "resets." I guess it is possible for the ARO valve to stick. If it happens again, I will try removing one of the valve wires to see if that makes a difference.
Thanks again for all the recommendations and trouble shooting procedures, and I will update of things change again.
|Very interesting info regarding the emission devices. As my car no longer has those items, removed by previous owners, my knowledge to how the emission controls operate is nil.|
I will follow your thread more closely to see how this comes to a resolution
|"I am a little confused about what could have been "fixed" by removing and then replacing the overflow hoses"|
It happens, which is when diagnosing a problem sometimes one does need to go back a step and check the fault is still there, before moving on to the next step and trying something else.
However hearing a click with the ignition going on before (which is not correct), but not now (which is correct), does indicate a problem with the electrics more than the plumbing, i.e. operating when it shouldn't have done.
Just out of interest, when the engine is running and you switch off, do you hear a click now as the oil pressure drops away? If not then the implication is that the valve isn't operating at all now :o)
|There is definitely a click when the ignition is turned off - as soon as the oil pressure drops off.|
Will try to get out of the garage today, and see if anything has changed, or returned, since it started working properly.
|Morning start and drive were very nice. Quick start-up, no audible click from the AOR valve. Smooth running and idle. Immediate shut down when key turned off - audible click from the AOR as soon as oil pressure dropped.|
One thing that I remember about the carb overflow ports. I had earlier disconnected them at the single juncture/split point, rather than from each carb, as I did this time. The single disconnect did not make a difference in the problem, but detaching both ports evidently did. Not sure if that adds anything to the saga, but figured I would note it.
I hate mystery problems, but really like early morning drives.
Thanks to all for the inputs, and I will update again if anything changes or returns.
|Congrats, Pat. I also hate mystery problems. I also hate mystery solutions. I get suspicious when suddenly it works. |
So in the end it was your carburetors along with some emissions items. ??
Hey get out there and enjoy it.
|As the clicking has changed from before to after, it's more likely to do with the electrical conditions. As to why, well you may well find out in time :o)|
|Well, I guess I knew it was too good to be true/permanent.|
This AM - back to the starting problem.
Disconnected the ARO valve, no change.
Reconnected ARO, and disconnected the carb overflow ports - started right up and ran fine.
Maybe time to re-think the previous time that I disconnected the overflow port hose at the "T" rather than at each carb. Could be a blockage on the way to the canister? Am I back to thinking "plumbing?"
Will see if it starts later in the day - I'm leaving the carb ports disconnected and ARO valve connected to see what happens.
The drive was still nice after it finally started - beautiful day.
|Sounds like your breather system is blocked somewhere indeed. If the overflow ports on the carbs can't equalise pressure with the 'outside world' then you will get no fuel flow as there is no pressure to push the fuel up the jet. Is it a legal requirement for you to have the emissions stuff working? If not, just run some pipes from the carb overflows down the side of the engine away from the exhaust and other hot bits and forget about it. This is how UK cars were all the way till production end, much simpler.|
|+1 to the comment above. I had a 79 many years ago & the overflow pipes got blocked/kinked. The car wouldnt run.|
|The overflow ports work the other way round. If they are blocked then the float can't rise, and fuel is pumped up straight up out of the jet flooding the engine.|
The way the anti-runon system works is by applying a slight suction to the overflow ports, which pulls the fuel out of the jets. If removing the overflow hoses allows the engine to start, it means that there is a suction from the canister on those hoses when there shouldn't be. Removing either or both hoses, from either Tee or carbs will break that suction on both carbs, allowing the engine to start.
Normally when it comes into play the anti-runon valve blocks the fresh air inlet into the bottom of the canister, so you have suction from the crankcase ventilation system plus a second hose from the inlet manifold to the valve creating the suction at the float chambers.
You need to check the charcoal granules in the canister aren't bunged up and causing a blockage, and the passage from there through the valve to the open air.
|Working my way through all the plumbing - between many other projects.|
Will update as changes occur.
Thanks again to all.
Paul, I do have a question about the ARO valve clicking. When I "test" it using the book method of detaching the wire from the oil pressure switch and grounding it - there is a "click" both when the ground starts and another when it is released. Could that be similar to what I had heard earlier when the ignition switch turned to "on"? Don't hear it now - except when oil pressure drops with ignition off, but I may have been listening too close earlier.
Anyway, back to all the plumbing (never have liked plumbing).
|I may be bouncing off multiple issues. Started blowing air through the various pipes and connections to the canister. Connected the overflow ports at the carbs, but disconnected the end at the canister, just to see if the pipe was clear.|
With the ARO still connected, I was back to the old starting problem. Disconnected it and heard a click. Re-connected it, heard a click. Disconnected the oil pressure switch, heard a click. Re-connected the switch, and heard a click.
So I tapped on the ARO valve and tried the oil pressure switch again - no click. Stuck ARO? Disconnected the ARO all together, and reconnected the overflow pipe to the canister, and it started fine.
Of course, I have had this happen before - seems to work, and the next day it is back to the problem.
Will wait until tomorrow to see.
I hate the idea of putting out the $ for a new ARO valve, but it is sure looking like it is the culprit.
Will continue to post updates, unless it is time to start a new/short thread.
|I have tried blowing air through the plumbing, and that has not turned up the answer. I am stepping through connections - starting with the overflow ports (since those allow smooth start when disconnected) - to try and discover the culprit.|
At this point, I have disconnected everything from the ARO valve and canister that go to the carbs or manifold. The only canister connections left are the one to the valve cover and one back to the gas separator.
With all this disconnected, the only way I can get a smooth start is with the overflow ports completely free. Even connecting the pipe with the "T" (which has been blown out with air) between them prevents smooth start.
Should the line that was connected between the ARO and the manifold be capped off or left open, when all this other stuff is disconnected? I disconnected it thinking that maybe the ARO was still somehow creating a vacuum there.
|First the valve. Yes, with the ignition off, if you ground the oil pressure switch wire you should hear a click, and again when you remove the ground.|
This should NOT happen with the ignition ON, i.e. no clicks when you ground the oil pressure switch wire. If it does, then the ignition switch is faulty - putting out 12v on the slate or grey wire when it shouldn't be.
With the engine stopped, you should NOT hear a click when you turn the ignition on and off. If you do then oil pressure switch is incorrect or faulty (stuck closed).
If disconnecting the valve from the canister allows it to start, with everything else connected, then either the valve is operated (closed) when it shouldn't be, or it is stuck shut, or the passage through it and its hoses is blocked. The last possibility should be easy to check - with it disconnected electrically you should be able to blow through it and its hoses.
If that is OK reconnect all the plumbing and leave the wires off.
If it starts now, but not when the wiring is connected, then the valve is being operated when it shouldn't be. But this is unlikely, as when you are trying to start it there should NOT be 12v coming from the ignition switch, and neither should there be a ground coming from the oil pressure switch - until the engine starts and builds pressure.
|Disconnected every line between the canister and the carbs, canister and separator, canister and ARO,canister and the valve cover, ARO and carbs, ARO and manifold, etc, etc. Blew air through all - no obstructions.|
Removed both canister and ARO. Changed the charcoal in the canister, and the top and bottom filters. Bench tested the ARO - opening and closing fine.
Checked wires to ARO - hot when ignition off, no voltage when ignition on.
Checked oil pressure switch - ok.
Re-connected all pipes and wires (I thought). Started up fine (thought I had it).
Realized I had not re-connected the "T" pipe between the carb overflow ports and the canister.
Re-connected that pipe - no start!
Removed the pipe again - starts.
The only click that is audible is when the oil pressure drops after ignition off.
|"Checked wires to ARO - hot when ignition off, no voltage when ignition on."|
Where did you connect your meter or test lamp? If between the two wires that go to the valve, and the engine was stopped with the ignition on, that is the fault.
You should only have voltage between the two wires at the valve when the ignition is off and there is still oil pressure from a recently running engine.
With the ignition on there should be no voltage (i.e. coming from the ignition switch) on the slate(grey) with respect to earth or ground, and with the engine stopped and no oil pressure there should be no earth on the slate/yellow from the oil switch.
You are trying to do too much at one time. Let's start from:
"Re-connected that pipe - no start!
Removed the pipe again - starts."
1. Reconnect that pipe, check that it still doesn't start, and remove the hose from the bottom of the canister. Start or no start?
2. If no start than the canister is blocked.
3. If that starts then reconnect the hose to the bottom of the canister but disconnect it from the valve. Start or no start?
4. If no start then that hose is blocked.
5. If that starts then reconnect the hose between the canister and the valve, and remove the hose from the bottom of the valve. Start or no start?
6. If that starts then that hose is blocked.
7. If no start then the valve is causing the problem. Disconnect the wires to the valve. Start or no start?
8. If no start then the valve is blocked or stuck closed.
9. If it starts with the wires off, but not when the wires are reconnected, then you have 12v AND earth at the valve, when strictly speaking you shouldn't have either.
Thanks for the detailed procedure - that will be my next attempt. I thought about doing too many things at once, but wanted to blow out all the pipes and hoses to check for obvious blockages.
As far as checking voltage at the ARO, I used a voltmeter between the slate wire and ground (without going through the ARO, to see if the ignition switch was doing something wrong). There was voltage when the ignition was off, and no voltage when the ignition was on. To "bench test" the ARO, I attached the slate side to the ARO with ignition off, and then grounded the slate/yellow side, to see if the valve would open in a condition similar to grounding that wire at the oil pressure switch. I looked into the valve and could see the valve open and close nicely, with the usual "click."
The only potential "blockage" that I noticed was that it was difficult to blow air through the pipe from the canister to the separation unit near the gas tank (with end open at the rear connection). Air would go through, but not easily. Other hoses and pipes all allowed air easily through.
I will next go through your steps carefully, and post the results.
|Guess I will have to take one step per day. With everything connected, it started - but not easily - minor backfire, but then kicked in. Like something was stuck, and then released. Problem is, it starts fine the rest of the day - issue seems to re-occur after sitting overnight.|
So tomorrow morning, I will leave the overflow connection alone, and remove the bottom hose on the canister.
|With hose removed from the bottom of the canister, it started - no backfire, but still not as smooth a start as I was getting with the overflow ports disconnected. Next step will reattach the hose to the canister, and remove it from the valve end.|
|Well, I finished all 9 steps - took a while because once it started (even if rough) it would be ok for quite a while.|
I just started it this morning, back with everything connected. Again, it started, but a bit reluctantly - although no backfire. Now it should start ok for the rest of the day.
The only thing I added to Paul's steps, was after the final one (and still not being able to find a "no start" combination), I sprayed electronic cleaner into the ARO. That seemed to work well - the next start was smooth and quick. Next day, however, back to rough start.
So, I am leaning toward a sticking ARO - once it frees itself on a rough start, it is ok until it sits for a while again.
At least it is starting, but I am still a bit confused as to why disconnecting the overflow ports would avoid the problem altogether.
|If the ARO is sticking closed, even partially, then removing the overflow hoses from the carb ports prevents the vacuum that the ARO causes to be generated from sucking the fuel out of the jets - if that is the cause.|
The ARO only operates for a few seconds when turning off a running engine. Once switched off the valve should be open, and stay open when the engine is next started and run, until it is switched off again. So leaving it to sit should not cause the problem to reappear, unless the valve never properly released i.e. opened at the previous switch-off.
If it is the ARO causing the rough start, then simply disconnecting the hose from between it and the canister should result in a clean start every time. If it doesn't, then something else is wrong, which as the problem is now 'only' a rough start and not a non-start, could be a completely different problem.
Thanks - guess I am in the "something else is wrong" "different problem" area - disconnecting the hose between the canister and the valve did not make it start smoothly. The only time I got a nice smooth start (with overflows connected) was just after spraying the valve with electronics cleaner.
Any chance the line between the canister and the separator could be the problem? I disconnected both ends and forced air through it, but the air did not flow easily. That is the only pipe/hose that did not allow easy air flow. I have heard that it is possible for a blockage there to cause a vacuum in the tank.
|You seem to be narrowing it down, disconnect the hose that goes between the carb overflows and the canister from the canister and see what effect that has. |
You may have too much suction on the canister from the rocker cover hose i.e. the crankcase ventilation system. If the test above gives a smooth start then reconnect the carb hose to the canister, check it is still a rough start, and disconnect the rocker cover hose from the canister and see what that does.
|Disconnected the hose from the overflows at the canister (after sitting all night). Same rough start. Disconnected the hose from the rocker cover at the canister - same rough start.|
During the process, the hose from the overflows to the canister had fallen off just after the "T" - smooth start. However, smooth starting after a rough start has occurred many times - I think the issue is identified, and the next day it is back.
I checked the fuel filler cap, and there was a significant "gush" when removed - even though I had only started the car for a minute or so. Seems like a bit much vacuum for such a short run-time and in relatively cool weather.
I will leave the connection that disconnected itself off over night, to make sure there is a difference.
|A gush from the filler cap when you have the vapour recovery system is definitely wrong, the tank should always be at atmospheric pressure. If it isn't then some component from the tank through the separator and to the canister is blocked. |
Unvented tanks with the vented filler cap will develop a slight vacuum as there is supposed to be a valve in the cap that only opens with slight vacuum, to prevent fuel trickling out in a roll-over.
This is now so inconsistent you do need to try just one thing over several days as you say. However as the situation before was non starting, and it is now starting but sometimes rough and sometimes not, I think you have cleared the original problem somewhere along the line and this is a separate issue.
|Spent some time today blowing air through the line between the canister and the separator. Seemed to start better, and ran very well, but still "gushed" when I turned off the ignition and opened the gas filler cap. Not sure how much that means, but I will try again after letting it sit over night.|
|Well, don't know if it is related to the starting issue, but the line between the separator and the canister is very badly blocked. Have tried air, wd-40, and weed-wacker line so far, but the clog is still there. The connection in the line next to the battery box was clear - the clog is closer to the engine bay.|
I left the connection open, and the car started pretty well, and ran well except for an occasional gas smell.
I am looking for alternatives to cutting the line, if possible - some sites recommend using a product called PB Blaster. Not familiar with it.
|If air won't shift it, then short of removing it so you can poke a stiff wire along it I'm not sure how you will be able to clear it. Has it been pinched anywhere? I don't know how this pipe runs as it was never on UK cars. You could poke a piece of copper wire into it while in situ and see how far it goes, then cut it at that point. AFAIK PB Blaster is for releasing seized threads, may not work on a non-corroding blockage.|
|The clog, which would not move or clear withwd-40, PB Blaster, and about 75 lb of air, was located several inches above the turn upward into the engine compartment. Also tried weed-whacker cord and stiffer metal wire, but neither could move it.|
Put the car up on ramps, and cut the line below the up-turn (easier access). The line was clear from that point back. Still could not budge the clog from below, so removed the line forward and up from that point. Found the exact point of blockage, and cut that part of the line out. Attached enough flexible fuel line to the upper/forward section so that it could be fed back down from the engine bay and re-attached at the canister and the aft-pointing vent line.
Not sure if this will make a difference in starting, but it should run better.
Will post results after a good run.
Thanks for all the inputs in this rather lengthy thread.
|This morning's run (after sitting for 2 days) - started up right away. Ran smoother, no spits, idle smooth.|
Back home - no gasp from the fuel tank.
Hope this means the end of this thread. Thanks to all for the great info and recommendations.
|Pat, Congrats for your persistence. These cars are old and many do not get used enough, hence problems... I've followed your thread and can relate to much do your issues. I would look at all your fuel and emissions lines. This may rise again.|
Thanks. It has been quite an ordeal. I have a feeling that I have been making adjustments over the years that may have been "working around" or covering up issues - and those issues finally became a series of problems. Using recommendations from this web site has certainly helped me realize that back to basics, and step by step approaches such as Paul's diagnostic procedures, are the way to troubleshoot.
Forums like this are sometimes the only way to get answers, as mechanics who can work on these older cars are becoming fewer in number all the time.
Here's to daily mgb driving!
|Pat. You are spot on. I too ran into an issue which turned out to be several issues that surfaced at the same time. Thankfully, with the wisdom and knowledge|
of Paul Hunt, Les Bengston, et al, it all sorted out.
Where in Connecticut do you live. I used to live in NYS on the Rchfield Danbury area
We live in the Southeast part of CT, but pass through your old areas a lot on trips south. CT roads (esp. highways) are not generally the best for any vehicle, but we do have some nice winding rural routes.
This thread was discussed between 23/04/2015 and 16/06/2015
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