I posted this on Pelican, and thought I'd try over here too. I have a 1986 930, all smog has been removed, no cat, O2 disconnected, and CO set to approx 2%. The car starts perfect cold, but after it has warmed up, if I shut down and let it sit for more than 5-10 minutes it is very difficult to start. I have checked the System and Control pressures and both are right on spec. The fuel pressure is still 1.4 bar after two hours of sitting. At this point I am at a loss as to what to try next. By the way, the Fuel Dist and Accumulator are two years old. The car has 54k miles, and runs perfect in every other way.

Tim

 

Non return valve? Read that somewhere so it's just a wild guess

 

Thanks, at this point I'll gladly take any wild guessing!, but I am not sure what specific part you are referring to. I would hope that any failure in the fuel system would show up in the system/control pressure testing.

Tim

 

when car doesn't start have you tried priming the injectors

 

Generally, if you have a hot start problem and your fuel pressure is holding, your injectors are bleeding off.

 

It could be the Auxiliary Air Regulator (AAR) this device controls the cold start or warm start, for that matter, and allows a certain amount of air to bypass the throttle body for idle control. You can take the hose from the Intercooler to the AAR off and shine a flashlight into the opening of the AAR. You should see the valve on the AAR with a slight opening. When the engine is fully warmed up you should see the valve completely closed.

 

I had a BMW 320i that did that and it was dirty-leaky CIS injectors.
Because CIS injectors stay open all the time while the motor is running they eventually get carbon built up at the tips in the valve making them not hold pressure and leak down after running.

The accumulator holds pressure on them after you shut it off to make starting quicker, but when the injectors leak or dribble gas after a hot shut down it actually floods the motor with too much gas and you have to crank and crank on the starter with the the throttle open a little way to get enough air in there to eventually clear it out and get it to start.

All that gas going in there thins out the oil thats on the cylinder walls and rings, and some is probably getting blown past the rings and mixing with the rest of the oil. Not a good thing...

 

Thanks! I find the AAR and leaking injectors to be very interesting, I'll ck both. But on the leaking injectors, if the injectors were leaking, would that not reduce system fuel pressure?

Tim

 

After thinking about the above replies a little more, I do have to hold the throttle(gas pedal) wide open when trying to reatart after shutting down hot, then lifting off the gas very very quickly just I the car begins to fire to keep it from reving up. I also smell alot of gas and have black smoke after it does finally start. But again, if my injectors are leaking, would I not see this in the System Pressure testing? (This car hold 1.4 bar for over 2 hours) or, are the lines going to the injectors on the other side of a check valve in the fuel dist and not part of system pressure?

I've also had the oil analyzed on the last two oil changes, and there are no signs of gas in the oil, so that is good!

Tim

 

Are the fuel pumps running? I think you can turn the key to the on position, take off the air box to gain access to the air plenum, and depress it down. I believe that will activate a switch and turn on the pumps (I read that in some other forum, but have not tried it). If the pumps aren't running at that point, then perhaps you've an issue with something as simple as a malfunctioning over-boost relay or sensor. More than likely, it's injector bleed-down flooding the engine as others have mentioned.

 

Both pumps are running. Car starts cold and runs perfect, just hard to start hot!

Tim

 

It's not the AAR valve. It has absolutely nothing to do with fuel delivery. It's a throttle body air bypass only and can't do what you are seeing.

The symptoms you have all point to the carbonized or dirty cis injector problem, and they may or may not completely leak down.
Have them professionally cleaned or buy new ones.

I have seen some guys put in a lot of techron injector cleaner when the gas tank is almost empty, run it then let it sit overnight, then start it and rev it up and clamp off the rubber fuel return line with a rag tripled up over the line and needle nose vise grips to clamp it shut.
Doing this raises the fuel pressure as high as the pump can make it and you will be dilluting the oil a little bit with the super rich mixture.
Do this a bunch of times...
Sometimes doing this will actually clean the injectors from the much higher pressure fuel with techron going through them enough to stop the leaking.

I'm not recommending you doing this though, just mentioning it because it is possible and alot cheaper...

Electronic injectors are constantly open ind closing from the solenoid so they are self cleanoing and don't have this problem.

It's also a good reason to always use Chevron premium gas if you can because it has techron in it.

 

So would I still have good System Pressure if the injectors are bleeding down?

 

The AAR has nothing to do with your problem. Leaking injectors will not show up on your guage as they are on the other side of the pressure regulator.

 

I'd try injector cleaner first. It worked for me.

Chevron's Techron is no better than Shell V-Power, or others' detergent additives when it comes to your Top Tier premiums. Regarding fuel quality and additives -- I highly recommend the following article:

http://www.usatoday.com/money/indust...gas-usat_N.htm


Unfortunately increasing ethanol content and low premium octane here in California (91) are our biggest fuel concerns.