Won't idle then dies after hot engine restart

[flora]

I have a 1987 automatic with reconditioned 1.9 DG water-cooled petrol engine that from cold starts and runs well with no problems. However, this (v hot) weekend on the way to a VW fest I stopped at a motorway service station, and when I restarted she caught but would not idle and hesitated when the throttle was blipped, eventually dying when I tried to move, and couldn't be restarted until she was stone cold, and a battery boost connected. Coming back she started as normal from cold and ran fine along 100 miles of motorway and other roads - I didn't stop!, but when I got home same thing - hot started but wouldn't idle, eventually died and wouldn't restart.

I am about to do a slow check through the ignition/fuel system, but has anyone had similar experience and found a possible cause?

Thanks, Flora

[slb1]

Hi Flora, I have what sounds like a very similar problem. Though mine is 1982 Aircooled. Sorry it's not very helpful! but would be keen to know the answer. Sarah

[kevtherev]

Air leaks into the induction side will weaken the mixture enough for it not to idle.
The choke would mask the weak mixture when the engine is cooler (cold starting)

Do you have the thick bakerlite gasket in place between the carb and manifold?

[flora]

Thanks for the point about air leaks and gaskets.
The carb has a 5 mm thick black insulating gasket, and the mechanical petrol pump has a 10mm thick black one. I have checked the various pipes linked to the inlet system, and everything seems to be fitted OK.
I hope to change the main starter battery today for a new Varta E38 . The fact that the engine wouldn't start after cutting out, even after cooling down, but burst into life when a boost battery was used, makes me wonder if the battery, although Bosch and only a few years old, might be a contributor.

Regards,
Flora

[flora]

Have fitted new battery this evening. Had to spin the engine for a while until it caught -carb fuel evaporation over 3 hot days since last running?
Did some hard 60 mph driving to get engine hot, went like a train, then back home and switched off.
After 10 minutes restarted with no problem.Drove back and forth on drive then idled. Switched off.
After further 15 min restarted (reluctantly) but wouldn't idle and had to keep blipping throttle, died if tried to move. Switched off.
After another 15 min, engine caught but died immediately and wouldn't restart.
After another hour, engine wouldn't start at all !!
Fuel starvation problem??
I will see if she starts tomorrow morning

Flora.

[Da dan]

When it happens next and it will check the fuel pump. I had the same. Changed to a electric fuel pump as it was struggling to get fuel in. Have you got a good spark? Hot start problems cool down no troubles. Just need to order a new one for spares. Check fuel lines while your at it.


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[Campermad]

I had similar .had aa out twice..had to clean rotar arm..and then spray easy start into air filter and bingo...sonethong about fuel draining back out of carb or sonething when its hot . What i do no is always pump the gas a good few times and then keep foot on pedal for every start..a bit like need a choke i guess.. dont know if it helps but thats what works for me
Lisa

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[flora]

Tried a cold start the following morning, following VW recommended procedure (see below). After extended churning she started and ran/idled normally. Looks like a fuel problem. The VW warm start is with full throttle!!

Official starting instructions from VW T25 manual
Cold start:
• Depress accelerator pedal slowly once (twice when it is freezing) and then release it.
• Start engine - do not use accelerator.
• If the engine does not start at once, stop using starter after 10 seconds, wait about half a minute and then try again.
Warm start:
• Depress pedal slowly while operating starter and hold it in the full throttle position - do not pump the pedal!
• Release pedal as soon as engine starts

Incidentally I have just found that there is at least one previous thread on this: http://forum.club8090.co.uk/viewtopic.php?f=37&t=150719" onclick="window.open(this.href);return false; that seemed to come to the same conclusion re fuel supply.

Probably worth replacing fuel pump although only 4 years old.

To be continued!

Flora

[flora]

I hope this is my last post on this.
Yesterday I removed the fuel line from the carb and had the engine cranked. Took a while for fuel to appear and then just about managed to pulse over the top of the pipe (held vertically level with carb). Clearly a problem with diaphragm.
Ordered a replacement fuel pump and fitted it today. Repeated above and got big spurts out.
Engine started as normal from cold. Got it hot. Waited 30 mins then tried a hot restart (as per VW procedure). Engine started and idled fine; no problem reversing up sloping drive.
Conclusions drawn? Almost certainly the main culprit was the fuel pump, but exacerbated by the inability of my original battery to spin the engine enough to get the fuel into the carb and then ignite it. As I found out in a trip last night, even with the original pump, the new battery would eventually get her started if the VW hot start procedure was followed.

Regards,
Flora