rough start when hot

[camshaftgsxr]

just bought the car but its a late 88 build (so 89 model year) 325is, it starts quite rough when hot and sometimes needs to crank a while before it will fire, then it sort of stumbles up to speed, once its idling though it runs fine and revs like a champ.

where should i start looking?

[603Racing]

I would start by checking the coil and spark. You can check the fuel pressure fairly easy as well.

[camshaftgsxr]

am i looking for a weak coil? the car runs fine after start up, its just a bitch to get to catch and start (its turning over fine)

[jlevie]

The first thing I would do would be to smoke test the engine to look for intake leaks.

[camshaftgsxr]

the iac is humming quite loudly and wasnt doing its job, there are a few small intake leaks where the two small plastic elbows that are on the side of the intake beside the throttle plate. ill have to seal them up, but the iac was stuck until i cleaned it and its still humming very loudly and probably not working properly still. do the "I" iac's humm louder than the eta iacs? my etas iac never hummed like that and i know it worked perfectly.

[camshaftgsxr]

The first thing I would do would be to smoke test the engine to look for intake leaks.

would the oil fill cap, oil dipstick cap, and the vent tube be part of the "intake" system and have to be sealed to avoid intake leaks?

[jlevie]

would the oil fill cap, oil dipstick cap, and the vent tube be part of the "intake" system and have to be sealed to avoid intake leaks?

Yes, along with the valve cover gaskets & bungs, and the oil return tube o-rings. To a lesser extent the front and rear main seals, intermediate shaft seals, and cam shaft seals, though those usually let you know there is a problem by leaking oil.

[camshaftgsxr]

Wouldn't a vacuum leak cause a lean condition? It is running so rich that its billowing black smoke. (But only part of the time). The afm is a known good part, the plugs were black and fouled I cleaned them for now since the parts stores are closed. can anyone tell me what voltage the oxygen sensors are supposed to put out. It is firing on all cylinders and has a good spark.

[paperplane94]

check the FPR as well

[camshaftgsxr]

check the FPR as well

how? it looks like a simple vacuum switch.. is there any way to test it?

i still dont see how to check fuel pressure yet either, i was all over the top of the motor last night and i didnt see a nipple or any connections

edit, it looks like you have to put a T fitting into the line some where.. can someone comfirm?

what pressure am i looking for in the fuel lines?

[603Racing]

Yes, you will need a fuel pressure gauge and T fitting to test fuel pressure at the rail. Is their fuel in the vacuum line for the fuel pressure regulator? If so, that's a sure sign the FPR is bad.

Fuel pressure should be 2.5 bar or about 36 psi. I think, LOL. I've been working on my e24 too much lately. It might be 3 bar ~ 44 psi. You can look at your FPR and it will have the bar value stamped on it.

[paperplane94]

^what he said...

Remove the vacuum line on the FPR. Smell the vacuum line. Fuel?

[camshaftgsxr]

Thanks! Ill have to check tomorrow, the transmission didn't want to cooperate and we fought with it all night to get it out.