Warm start problem

[ronb]

When warm, it's 3 very very long cranks, and then a sputtering start which has to be nursed with the throttle. I've replaced the WUR and the cold start valve, the fuel accumulator and the fuel pump (that was to remedy OTHER starting problems)

When cold it starts immediately, when hot it starts immediately. If it's warm and catches and then stalls, it's a long process...ie a long series of long cranks, before the engine will catch and start. Is this perhaps just an example of 25 year old CIS? Will it deteriorate? What can I do to straighten this out? A few people at the last DE I was at seemed to think this was normal, however I don't think this would have been acceptable even 25 years ago, as a normal funtionality.

[Superman]

Nope. Not normal. You should expect nearly instant starts and smooth, excellent running at all temperatures, if everything is working properly. I'm at a loss to guess what might be wrong, but troubleshooting the CIS system virtually begins with cold and warm fuel pressure tests.

[ronb]

One more point - how much throttle should I be using to aid in starting? Ideally none I know, however, if I have it 1/2way down for the warm start, and then squeeze on full, I can start it much easier, usually about 70% of the time...am I correct in assuming some sort of pressure issue?

[MotoSook]

If your idle mixture is set too far one way or the other, it will act like you describe some times. Judging from the easy cold start and hard warm start, you may be lean. Why! When the WUR is warm (car warm), it enriches less or non at all! When it fires, then dies, the CS valve provides just enough enriching to start then cuts out, then the CIS has to take over, but if it is not set correctly, it will die.

When you replaced the fuel pump, did you put in a new check valve? Have to ask.

As super said, all this is guessing until you know what you fuel pressures are.


From your last post, I really suspect a poorly set idle mixture. Try to turn the idle mixture valve about 1/8 turn clockwise to richen it up. Or take it to an place that has a CO monitor and set it right.

[Joe Bob]

Check valve.....

[Bob's Flat-Six]

Ron,
I had the same problem on my 80, if it sat half hour or so it didn't want to fire right off.
It was explained to me as fuel bleed off problem and the fuel pressure acumulator was replaced and the fuel pump check valve.
My tech said when cold the cold start system would help start the car. And as I recall it would run rough until enough fuel was picked up, not hitting on all 6.
When warm the cold start system doesn't kick in so theres not enough fuel to fire right off.
You might do a search as this is a fairly common problem. Or somebody else can help explain if I missed anything?

[Joe Bob]

Oh yeah.....if you are stranded and it does that....it will fire on quick start, and then the pressure will catch up and it will run......

Best way is to have someone cranking and a small shot in the intake will do it.

[Bob's Flat-Six]

Hey Mike,
I'm around diesels alot and have seen guys take a rag soaked in gas and rap it around the air intake and it helps fire them.
Hmmm, probably couldn't hurt if you were stranded ?

[Joe Bob]

Good idea....it's a pain, doing a shot and running to the starter.....

[Bob's Flat-Six]

Hmmm, on second thought a rag soaked in gas could start more than the car Back to the drawing board or check valve.

[ronb]

Thanks for all the replies...yes, check valve was replaced as well. Is the consensus then to adjust the mixture?

[Joe Bob]

No....check the fuel pressures....both hot and cold. THEN mixture.

[john walker's workshop]

in the meantime, simply slipping out the air filter unit, and lifting the sensor plate arm with the key on, will squirt the injectors and allow the car to start readily. 2 seconds is enough, you'll hear them whirr. not a fix, but gets it started with little hassle.

[ronb]

...as I unhooked airbox to lift plate to restart car to go borrow fuel pressure tester, I saw that the airbox was not seated correctly, ie there was a gap. I am now enroute to get the fuel pressure tester, but is there any chance that a poorly fitting airbox could be the issue? ie causing some sort of slight mixture alteration, only noticable under warm start conditions?

[john walker's workshop]

gap? where exactly? could be the airbox blew apart on one of those intake backfires. happens all the time. are the little screws sticking out a bit? that's the first clue.

My 79 is doing the same dance. I'm installing a fool pump check later this aft in hopes that is it.

Souk, I didn't know the mixture would cause the same thing. Thanks

[ronb]

I am set to do the pressure testing tomorrow. John, the gap I refer to is not a split, but rather that the 2 pieces were not fitting together tightly, ie the top piece was not sitting in the bottom receptacle, and so instead of being sealed, had an open 1/4" space all around the bottom. Would that have been enough to lean it out? Because, after the recent re-sort and replacment of the components listed above, it functioned fine at all temps, this was a new development as of after bringing it back on the road this March. And, it has been functioning somewhat better since I put the airbox back together correctly, ie during my trip to get the pressure gauge and other tools needed to do the testing.

[john walker's workshop]

i guess you mean that the air cleaner was not seated. that would make no difference.

[ronb]

yes, my apologies; it seemed odd that would make a difference. Will do the testing tomorrow afternoon and let you know. Thanks for all yr help.

[ronb]

All pressures are within the spec in the bentley manual. Mixture? Injectors? Fuel distributor? WUR? Where to start looking?