Troubleshooting Occasional Long-Start Condition

[crazyd]

I just finished putting another '95 DOHC engine into my '92 5-speed GTP and have worked out all the other bugs, but there's one left that I thought I'd ask the forum if it's a common one before I do a deep dive.

Sometimes it's taking the engine a long time to start when warm. If it's bone cold it'll always start immediately. If it's been off more than 5 minutes or less than 7 hours, it will sometimes take a good 15 seconds or more of cranking to start, but it's not consistent.

I know the fuel pump relies on the oil pressure switch to close at 4psi, and this engine came from a '95 MC that didn't have the gauge, only a light. After I changed this to a proper gauge sender, it still has this problem.

I was initially thinking it might have been the fuel pump or a leaky injector, but the fact that it always starts when cold would seem to rule that out, and the injectors were sparkling clean when I installed them. I haven't looked at the fuel pressure yet.

It did this before on the previous '95 Cutty DOHC I had in it too. I brought over the plenum, injector rail, harness, and most sensors from the old engine to the new one, but as far as I understand it only the TPS is queried in the pre-catch start sequence - and that came over with the plenum. So it could be the problem if its baseline voltage is much higher than 0.54. I haven't tested this yet but I don't think it's the culprit since the car otherwise runs fine.

Thoughts and suggestions welcome.

Thanks,
Dave D

[walterdude]

My 93 had pretty much the same issue,,, TWICE!!! It was the Fuel Pressure Regulator both times... The first replacement only lasted a few months,,, GGGRRRR.... I'd run a fuel pressure check and see if it gets up to pressure/holds it.... There's a Schraeder (sp?) valve tucked in by the power steering pump for this purpose.... Another check would be if you can get to the vacuum line going to the FPR, check that for gas and or gas smell... On a 93 the line runs to the MAP sensor and you can pull the vacuum line there,,, not 100% sure but, I don't think 95 had a MAP sensor... You'd have to find where it gets vacuum from and check there...
The 2nd time the car would NOT start when warm,, had to start cold and not shut it off until it could have a few hours to cool down.... FUN!!!
If you don't have a pressure tester you could probably borrow/rent one from an Auto-Parts Store....
That would give an indication of how the fuel pump is working also...
Hope this helps,
Tom

[crazyd]

Thanks Tom, since this is a hybrid 92/95 setup it still uses the MAP sensor due to the ECM/harness being specific for the manual tranny that didn't exist in '95. It just ignores the crank and cam position sensors. I've got a fuel pressure gauge, I'll check it and the regulator line. This hasn't happened at all in the past two days, so if I'm lucky it's just something that got sticky from a year of rebuilding and with regular exercise is coming unstuck.

[walterdude]

Yeah, I noticed you swapped stuff, AFTER I posted.... The idea is still the same.... According to Haynes you're looking for 40-47 PSI,,,, when you start it it should drop by 3-10 PSI. Those are a good indicator of the pump's condition. Of course what you're looking for is if the pressure holds, it should hold pressure almost indefinately..
Good Luck!!
Tom....
Post whatever you find...

[pocket-rocket]

Also take the vacuum line off of the FPR and see if fuel comes out of the vacuum port on it. If it does, the diaphragm in the FPR has a hole in it and the FPR needs to be changed.

[walterdude]

From my experience you can't get to FPR without removing UIM,, that's why I suggested unplugging the other end of that line from the MAP and looking/smelling for gas in the line. Mine had gas all the way up there,,, because there WAS a hole in the diaphragm. Also I have heard of sucking enough gas into the intake to cause more problems. That's just a quick check tho, a pressure gauge (he has one, might as well be sure) will tell a lot more including about the fuel pump.
I think that is where the problem lies (FPR),,, could be/have been wrong before, though!!
Tom....

[pocket-rocket]

I saw tons-o-text so I skimmed, lol. I have been wrong too, but it's not so easy to diagnose cars over the net every time, but at least people like us try to help

[no_doz]

lol i appreciate the help-i was just like huh?