yota-toy

I've seen a few threads regarding this issue. I have an '86 that runs tip top cold and won't run warm. I've been down the list, vacuum, cold start valve, ign, etc, etc. This seems to be the last item checked for most. If this is a normal fault, what causes it to "just happen" and is there anyway for a normal mechanic (as in, not a tech, like me)to correct said problem.
I have no problem taking it to a mechanic to help stimulate our economy but the car has no master cylinder, dashboard, doors, you know the deal. It's a parts car with an engine I'm hoping to use in my quattro. Thanks in advance!!

MarkPan

Sounds like the warm up regulator to me.

It reduces pressure on top of the piston in the fuel distributor when cold, effectively making it easier for the air to open the valve (and enriching the mixture). Now once it warms up, it increases the pressure, leaning it a bit.

If it doesn't up the pressure when it's warm, it will run too rich.. and ****ty. If it overdoes it, it will be too lean.. and run ****ty.


The other thing I can think of, from past experience... When a fuel pump is on the way out, but not right out... It pumps less fuel once it gets hot, and you lean out... eventually it gets worse, and doesn't even work well cold, or stops altogether...

yota-toy

The warm up regulator, is that the small block located mid engine with two fuel lines running to it and the fuel distributor? Is it rebuild or adjustable? And is it only on turbo cars (didn't see one on my '88 non-turbo.
I don't suspect the fuel pump only because the problem follows the engine temp. The car usually will not restart once it's warm. It seems to me that the fuel pump would cool faster and begin working again.
thanks for the info!!

audi_marv

also check your ecu and idle temp sensors at the front of the cylinder head. they may be out of spec.

Kneale Brownson

So it quits when it gets hot, or just runs poorly? If it quits and doesn't want to restart, see if the tach needle moves while cranking the starter. You could have a failing engine speed sensor. When they die, the ECU doesn't get a signal to allow spark. And the tach doesn't move.

yota-toy

It'll run once it gets hot but won't drive, engine pops and won't rev. I'm thinking the tach moved when cranking (it works while it runs). The engine speed sensor is the grey pick-up on the bell housing right? if memory serves right these two bellhousing sensors are interchangable?

Firechicken

Yes you have it right, you can swap the 2 crank and rpm sensors over to see if one's going bad. They are natorious for not working once they get hot....well not natorious but it's been a common faliure. And having the Tach working before makes no difference, you want to know if the tach is moving upon cranking when it's NOT starting..... right.


Also do not discount the fuel pump just because you think it's doing the poor/not running that cycles with engine temp, I JUST REPLACED a fuel pump that did almost a very similar thing, it'd run for a bit, and once it started getting warm it'd dropout it's pressure output quite drasticaly. car would die, and not start till everything including the engine were stone cold again.

Once the car starts getting close to the point where you know it's gonna get ready to quit soon, take notice of how many RPM's you can get out of the engine, like under a bit of a load are you having trouble getting it past 3k RPM over half and up throttle? If you are, then most likely fuel system, if you've checked usual suspects like plugs wires ect ect, again my pump did this before replacing. Unlike Pure EFI cars, these CIS systems Must have and rely on having very accurate control of the Fuel system's pressures, be it at the WUR, Pressure valve, whatever, they will start to get pissy once fuel volume from pump drops out a bit, aswell as other things.

yota-toy

Firechicken, I read your response and now I'm thinking more toward the fuel pump. the engine struggles to rev past 4k rpm. I'm sure whatever the prob. is it won' t matter much since the engine will soon be a donor to my new to me 5ktq. Thanks!!