Another "HOT START" problem

[Hirevtuner]

Ok I know this has been discussed before but I can't seem to solve this problem.
Starts and runs great cold. If I stop and start it right away warm no problem, but let it sit for 20 min. and I have to crank and crank to fire it up and then runs great.
Warm system pressure is bleeding down to fast. I have replaced the fuel accumulator twice, coil,cold start valve, WUR, front fuel pump check valve. Injectors were cleaned and tested which Chris at Turbo Kraft assures me are not the problem and also thinks not a fuel head issue as it runs so great when it runs.
I'm missing something here. Any idea's?

[Hirevtuner]

As an update I have make no further changes other then putting some miles on it and it seems a little better on the hot starting. Not perfect but better.......something cleaning itself out maybe?

[mark houghton]

New plugs...just to rule them out anyway? Check your ignition timing lately? Could be your CDI is starting to fail, getting heat soaked when sitting hot. Just some thoughts, no concrete answer yet.

Mine starts up in the first 1/2 second of cranking when hot.

[Hirevtuner]

New plugs, cap, rotor, wires, fuel filter. Timing is checked.
Runs great just won't start quick when hot.

[mark houghton]

OK, so you've spent a zillion bucks replacing everything you can touch. Are you running with the stock CDI, or perhaps MSD or Permatune aftermarket setups? There isn't much left to look at other than maybe a weak spark when she's hot. Not much help....sorry. Sit tight, others will surely respond.

[Hirevtuner]

Stock CDI Mark. Ruled that out based on how well it runs hot when it runs but maybe I'm looking at it wrong. I should spend more time with my test gages but man these things are not easy to work on.

[mark houghton]

Originally Posted by Hirevtuner

Stock CDI Mark. Ruled that out based on how well it runs hot when it runs but maybe I'm looking at it wrong. I should spend more time with my test gages but man these things are not easy to work on.

Things gain temperature for a few minutes after engine shutdown, with no air circulating to cool stuff off. Residudual heat just bakes the engine even when she's "cooling down". I'm still thinking you've got a $hit spark when hot, but I'm just theorizing at this point. Know anybody with a CDI you can borrow, to rule it out?

[mooney265]

I would try to enrichen your idle mixture and/or possibly lower your cold CP. I had a similar problem, then did just that [for another reason] and accidently fixed the problem... Turns out, it was starving for fuel on warm re-starts...

Just a thought...

[full quack]

Ok, I'll chime in and say, just because your injectors were cleaned does not mean that one is still not leaking down when shut off hot. I chased that gremlin for 2 years, I too did everything you have done.
Then out of pure frustration, I finally pulled the injectors AGAIN and had them checked and cleaned AGAIN. Finally now the car starts any time , anywhere, any temperature, any time sitting. Less than 2 revolutions and she fires right up.
My car did that very exact thing from the first day I bought it. I changed the check valves, the pumps, full tune up, full wires, BRL adj. warmup regulator, 2 new coils, new distributor wire, plugged this hose-plugged that hose, adjusted this-adjusted that, blah blah, blah.
Try the injectors again my friend.
Mark

[Helmsy]

You said you have replaced the WUR. With a BL WUR? Have you got the gauges to check your fuel pressures?

[gogomobil]

same hotstart problem here. after hotstart the idle afrs are far too lean, around 17. cruising afrs are fine. coldstart idles are fine. does your car have an afr gauge installed? my speculation too is that after sitting and heatsoaking, the fuelpressure leaks away somewhere.

[Hirevtuner]

Thanks for the input.
I show a drop in warm fuel pressure between the fuel head and WUR, in fact it will zero out in about 5 min after bringing it to full pressure.
I will try and get another set of injectors to try.

[mark '87 930]

Replace your fuel accumulator. It's a crappy $250 part that offers no additional power or efficiency.. but the car will start right up after.

[Hirevtuner]

Replaced it with a spare and then bought a new one but still no change.

[mark '87 930]

check-valve at the front pump? (Not sure if your car has one).

[Hirevtuner]

81 930 has a front fuel pump check valve and I replaced it.

[mark '87 930]

i just noticed you wrote all that in your first post, sorry about that.

Once your pressure is at 0 (after 5 mins), have you tried turning the key to on and running your pumps? if so, what does your fuel pressure read then (without trying to start the car).

Have you check to see if you are getting spark after that time?

[x98boardwell]

I had the same issue for a while. I replaced the fuel accumulator and it helped alomost everything. I realize you have replaced yours twice so that is probably fine.

My issue continued and I finally found out it was an air-leak. The motor heat soaked after driving and then the little air leak would turn into a large one. The AFR's would be very lean (very hard to start) and as soon as I was able to get some air in the system and it cooled everything down the leak tightened back up and went away, normally after cranking and holding the pedal down to keep it running.

Not a guarantee but worth a shot. You could use a spray bottle filled with very soapy water on the motor before you start after heat soak.. then look for bubbles. Make sure you have good light all over so the visibility is good. It could be around your inter-cooler area, turbo up pipe, by the throttle body or even the injector blocks (which I know are hard to see).

Let us know what happens. With everything that you have already done this is nothing. Best of luck,

Bryan

[mark houghton]

Originally Posted by Hirevtuner

Thanks for the input.
I show a drop in warm fuel pressure between the fuel head and WUR, in fact it will zero out in about 5 min after bringing it to full pressure.
I will try and get another set of injectors to try.

Are you saying that your system pressure (normally around 6.8 to 7.0 bar) is dropping to zero? That's like no bueno, amigo. Gummy fuel distributor, maybe. Have you taken out the pressure regulator from the fuel head and checked to see that it's not all gooed up?

[Hirevtuner]

Well maybe not zero. I removed the gauge at 1 bar but it did drop fast.
Do you think the fuel head would be the offender? It runs great once started.