Heckler

I'm stumped (though that's not saying much), and I could really use some suggestions.

My '90 3.1L Firebird has a really weird problem. I'll do my best to describe it, then I'll describe what I've done in failing to fix it.

If you run the car for 15 minutes or more, then turn it off for ~10 minutes or more, it won't re-start. If you turn it off and immediately try to restart, it will start (though kinda rough). If you leave it sitting for 3+ hours and try to start, it will start. But if it's been off for between 10 minutes and 3 hours after running for awhile, it won't start.

It definitely has spark, and if you squirt a little starting fluid into the intake, it fires up for a second (which means no fuel). The fuel pump and fuel filter are about 10 months old, and I don't have the right fitting to test fuel rail pressure so I haven't done that yet -- but I have simply vented the fuel rail test connection, and there's enough pressure to geyser up about 6 inches. I can hear the fuel pump click on when I turn the key and the fuel rail pressure seems to increase each time it does (again, just judging by the geyser height following each start attempt).


My question for you pros is this: What sort of problem between the fuel tank and the intake manifold could cause an intermittent problem like this? Is there some return fuel line that might be stuck open, or could the fuel filter possibly cause an intermittent problem like this (there's only about 500 miles on this fuel filter)?

I'm stumped because of the intermittent nature of the problem (meaning it can't be a constant issue like a clogged filter), and because starting fluid will fire (meaning everything downstream of the injectors is working). Anyone got any advice on what I could check next? I can't think of anything that would only happen for ~3 hours after warming up then disappear.

I sincerely apologize if this is a common issue that could have been found with the search or common knowledge -- I did my best with Google and couldn't find anything. This board has easily been the most helpful resource available in the past, and I'm simply out of ideas and about ready to buy a Corolla

EDIT: There's no codes, and the car runs perfectly fine once it's running.

project89

iTrader: (1)

i have seen fuel filters clog and act just like ur are saying.

few years ago we had a tpi vette in the shop, same symptoms u are describbing the only thing different is u could start the car and drive a few miles and then it would stall and wouldnt refire.

but use some starting fluid and it would fire up but then die again due to no fuel.

let it sit for an hour or 2 and it would do the same thing



when u try to start the car in that 10min to 3 hour window do u smell alot of fuel?
if so u could have the injectors leaking down with the engine off and flooding the engine

i would deff get a way to test fuel presure, i didnt have the correct fitting for my iroc so what i did is remove the valve core from the fitting on the fuel rial and clamped a rubber hose on it with a hose clamp and then clamped that onto the back of an oil presure gauge i had laying around.

be aware do not drive around with that as it is very possible for the hose to come off the back of the gauge or the fitting on the fuel rail even with the clamp on it. but its a nice cheap way of checking fuel presure in ur driveway/garage real fast

Heckler

Ah wow, I didn't realize a fuel filter could cause intermittent problems like that. I drive the car about 10 miles at a time, and it always makes it (assuming it starts) -- but maybe if I kept driving it would eventually stall out.

But no, when it's not starting, I definitely don't smell fuel anywhere. Since the most recent work I've done was on the fuel pump, I was actively looking for fuel odors and couldn't find anything.

But -- If the fuel rail pressure is the only logical thing to do next, I'll just have to go find a fitting and gauge. Thanks for the info!

project89

iTrader: (1)

when u changed the fuel pump or worked on it did u use submersible fuel line in the tank?
regualr fuel line hose swells up when soaked in gasoline and will leak internally in the tank, and or split

whenever u replace a pump u have to make sure u use submersible fuel hose

Heckler

I didn't change any of the fuel lines internal to the tank, I actually cut into the trunk and hacksawed the 4 lines in order to get the old one out -- but aside from the new pump and filter-sleeve, everything in the fuel tank is factory (my hacksaw work could have clogged the filter, so I'm probably just going to swap it out and see).

The new hoses I used where I spliced the two metal pipes (edit: the two halves of each of the four fuel lines) together was designed for high pressure fuel lines, and I can still see it though the hole in the trunk and they look fine (from the outside). I would think if they were swelled up internally, the problem would be more persistent. Early morning and after work, it fires right up and gets me where I need to go (it just won't restart once I'm there, for 3 hours).

project89

iTrader: (1)

the line son the outside wont be an issue.

alot of ppl dont relize that the line inside the tank that connects the pump to the top top of the sending unit assembly is special, if u use standard high presure fuel line there, that is when u get the swelling and leaking problems

heres my fuel pump assembly out of my twin turbo iroc the lines im talking about are the rubber lines above the pumps, but if u still have the factory line in there then it shouldnt be an issue

Heckler

Ahh, I'll have to look for the picture I took of my unit, but I definitely didn't replace any of the line internal to the tank (The only "new" line I used was to splice together the lines I hacksawed, external to the tank). That's good to know though.

Base91

iTrader: (1)

It sounds most like the fuel pressure regulator is bad. Pull the vac line off and smell for gas in the vac line or look for any drips. When the diaphragm starts to leak gas gets to the vacuum side and gets sucked into the intake on a warm start and totally messes up the idle. On a warm start can you play with the gas pedal and get it to start running?

Heckler

No, it doesn't even sputter (no matter what I do) inside that 10 minutes to 3 hours window. If it's been off for ~3 hours it's a little sputtery while it's starting but totally fine once it's running. If it's been off all night/all day, it fires right up like a champ and runs fine all the way to work.

I will check for gas smell in the vacuum line though, I've had vacuum headaches forever. If I had a severe vacuum leak, could that cause the fuel pressure regulator to act funny only on a warm restart?

RBob

iTrader: (1)

If the fuel pressure checks out OK the problem may be the injectors. The OEM Multec injectors are known to short the coils. More so when hot, and when enough of them short none of the fire.

RBob.

Base91

iTrader: (1)

I've had the injector and the regulator issues. One bad injector can stop the car running. It'll fire but not run. Given the age of our cars, if they haven't been done that you know of, get a set of injectors (southbayfuelinjectors.com ?) and rebuild the regulator. Then you have a solid starting point and don't need to keep removing the manifold etc.

Heckler

Thanks for all the info so far. After doing some reading, I'm leaning towards an ECM related problem. I'm looking for more detailed information on the ins/outs of the ECM and how it controls the injectors. Because the problem seems to vanish completely once the car starts up, I have a hard time blaming the injectors themselves. Seems to me if 1 or 2 were drastically misbehaving, I would see symptoms all the time. Since the car doesn't even try to sputter a little when it's acting up, I feel like all 6 injectors are just not injecting -- and as far as I know, the only thing capable of making that happen is the ECM.

I don't know much about the ECM though, maybe it's impossible. I'm just wondering if it's getting some bad input from one of its sensors, or maybe that the ECM itself is faulty (never been replaced).

That being said, fuel pressure will be the first thing I check once I have time to get into it this weekend.

Heckler

So the car wouldn't start at all this morning, even after sitting all night. But I played with fuses for about 30 minutes and got some more symptoms:

With fuses INJ1 and INJ2 installed, the car is sputtery and the longest I got it to "run" was about 1.5 seconds.

With INJ2 installed and INJ1 removed, it will start and run (rough). If I insert INJ1 while the car is running, it immediately dies. I was thinking it's probably not good to run on half the cylinders (worrying about uneven heating, not sure if that's actually a problem), so I didn't let it run too long like this. But it reliably fires up with INJ1 removed.

But, with INJ1 installed and INJ2 removed, it won't start and doesn't even sputter.

I was thinking that this could still be a pressure problem, like the pressure is high enough to support half the injectors, but not all -- but since it acts differently when you swap which injector set fuse is installed, I don't think that can be right. So I think the issue must be in one or more of the INJ1 injectors.

Sound reasonable? Also... which injectors are on INJ1?

RBob

iTrader: (1)

Sounds like some injectors are shorting out. Pull the INJ1 fuse and it takes those three injectors out of the loop. So that the remaining 3 injectors can be fired by the ECM.

Big note here, there is only one injector driver in the ECM. All six injectors are fired at the same time by the one driver.

RBob.

Base91

iTrader: (1)

Bite the bullet and do the injectors and regulator. Then you shouldn't need to take the top off again.

Heckler

I'm checking out the wiring diagram, and it appears to have 2 drivers (one per fuse -- ECM C2, pins C11&C12). Are these pins the same internal to the ECM black box or something?

I also can't find any specific instructions for removing the intake plenum -- is it just unbolt and remove? And to verify, I'm looking for 12+ ohms on each injector coil correct? Lastly, if I find 1 clearly bad injector, do you think it would be "safe" to leave that injector wire disconnected and limp it home (10 miles) on 5 injectors?

Base91

iTrader: (1)

Mine shut down completely with one bad injector. No limp home. Just because the ohms are good doesn't mean the injector isn't clogged or there is some other issue.

RBob

iTrader: (1)

Yes, one driver, the two ECM connector pins are tied together inside of the ECM.

Yes to limping it home. Also unplug the O2 sensor to prevent it from going into closed loop.

The plenum basically unbolts. It's been a while, and the car I replaced the injectors on also had the TB water heating hoses bypassed. Unbolted the plenum then rolled it forward and left it sitting there upside down. Didn't unbolt the TB or disconnect the cables from it.

Do not disconnect the fuel lines from the injector block/rail. There are some fuel line clamps to remove that will allow the injector block to be lifted enough to R&R the injectors.

RBob.

Heckler

Great, thanks for the info RBob. I pulled the connector off the passenger-front injector today and the car fired up (sort of rough, but not nearly as bad as with the fuse pulled). I'll limp it home tomorrow and do the injector job. Hopefully that will solve the problem.

Thanks a million guys, I'll keep you posted if the fix works.

Heckler

So I tested the injectors and the bad one was only 1.2 ohms. Swapped in a new one and the car is running great. Thanks for all the help guys.