RichieGTA

I have a very stumping problem with my 89 GTA 5.7.I am a mechanic with almost 20 years experiance and run my own racing operation,but this one has me totally stumped.

First I will describe the problem,then I will describe the history.If I go out to a stone cold engine it starts after a few revolutions and runs fine.If I shut it off before it is totally warmed up,it wont restart on it's own,but will restart if I shoot a little carb cleaner into the throttle body.If I get it up to full tempature and shut it off,it will restart most of the time but it does so after a good bit of cranking.During all of this the starter is cranking more then fast enough to start the engine.

Here is the issue.The car did this once back during last winter,but never after that,until about 2 months ago when I decided to pull the intake off to change the lifters.I have had this engine apart before so I was pretty familiar with how to put it back together.The engine had a loud lifter tick which I figured I would fix before I started cruising the car heavily in the summer.

So here is what I have done so far to fix it.I put a fuel pressure guage on it.It holds 45 psi with the key on not running.When I shut the key off it drops slowy to about 25 psi over a period of about 3 minutes.I put a "bug light" into one of the injector plugs during a no start condition and it had injector pulse.It has spark when it is not starting.I figured maybe the distributor was messed up and not sending a good signal while cranking so I replaced it along with the cap rotor and plugs and checked the wires.The car has an MSD coil BTW.I replaced the coolant temp sensor and the air temp sensor.I drove the car for a while and checked for codes and the only thing I got was a code 42{spark signal I think} which may have been stored from before I replaced the distributor.I reset it after doing this work and drove it some more and now it has no codes.I bought a book.I checked every vacum hose,and replaced a few,everything that should make it start is there.The only thing bootleg on it is that the EGR valve has the hoses in and out of the selinoid but has nothing else hooked to it.It has been like this for a while though.I set the timing both after the lifter job and after the distributor change.I was thinking about swapping out the ECU,but thats kind of expensive.I saw on the wiring diagram that there is supposed to be a wire that runs from the crank wire that engages the starter to the ECU which activates the start mode.I was wondering where this wire is hooked to.Last year I replaced the oil pump in the engine and had the starter down.The wires were pretty ratty,but wanted to do a starter in the near future so I figured I would just put it back together for now.Does the wire that activated the start mode go all the way down to the starter?It seemed like the start mode could be the problem since on cold start it would increase injector pulse just to get the cold start,and at hot start it wouldnt need that much more fuel then the normal injector pulse would provide.It all has me stumped.

Thanks for reading this far into the post.Hopefully somebody has seen this problem before.

86TpiTransAm

It sounds more like a fuel delivery issue to me than a starter issue. I believe the crank wire actually goes to the starter enable relay which is in turn wired to the VATS module. If I recall correctly, the VATS module reads the key for the correct resistance and if the value is correct it then creates a ground to energize the starter enable relay and allow voltage through the crank wire to turn the starter.

As far as the fuel delivery problem goes, it's obviously not fuel vapor lock since that's not possible at higher PSI that the TPI units run at. However, the TPI unit is not supposed to bleed off the fuel pressure that quickly. Yes, it does bleed off the fuel pressure but not that much in 3 minutes. I believe you may have a faulty fuel pressure regulator. The diaphragm in the regulator is probably ripped or has a hole in it and allows faster bleed off time after the engine is shut down. It may be so bad that it has a problem getting the fuel pressure back up during cranking and that's why it's so hard to start. It makes sense that it would be easier to start when cold because the ECM and MAP sensor act in the same sense that the cold start injector did on the earlier versions of TPI and allows more fuel to the engine for cold start.

I'm fairly certain that could be your problem but if not, you may just have a weak fuel pump. It could be that it's just weak starting up but once the engine gets going, the fuel pump can keep up.

RichieGTA

Thanks for your imput.I was wondering about the bleed off.None of the plus are wet or fouled so I doubted it was a bad injector,by the regualtor could be the problem.Tgis car doesnt have a cold start sensor or a MAP.

86TpiTransAm

I apologize, you are correct about the MAP sensor. The 89 still had the MAF (Mass Air Flow) sensor. The cold start injector (aka the 9th injector) was eliminated in 88 I believe (I know the 87 still had it) and a cold start table was added to the computer chip. During cold start the ECM uses the cold start fuel table to supply more fuel and once the engine reaches a certain temp it switches over to the normal fuel table.

Definitely check out the fuel pressure regulator. It's a pretty easy removal but you'll need the small torx bit with the little hole in the end of it since GM used the safety torx bolts on the FPR. Of course make sure you wrap some rags around the bleed off valve on the fuel rail and remove the shrader valve to completely bleed of the fuel pressure before you do the FPR removal. You should be able to get the torx bit you need at any parts store (I know for sure that O'Reilly Auto Parts carries them if you have one nearby).

EDIT:
You don't have an O'Reilly Auto Parts. We're not that far up on the east coast yet. Closest state to you with one is probably Ohio or North Carolina, neither of which are really even that close.

RichieGTA

Here is one more interesting little symptom.I just noticed today.I dont know if it has been happening all along,but this morning after I drove the car to work I attempted a hot restart which was a failed attempt.During the engine cranking the tach flailed back and forth wildly.Whazzup wit dat?

Jza

I'd do some basic troubleshooting on the Coolant Temp Sensor. It can give all kinds of fuel-delivery symptoms that will mislead you to other areas. They're actually cheap enough I just go ahead and replace it if it's on a car that still has the original.

You might also check the grounds (straps, etc).. Conductivity is often temperature-dependant and can give you goofy exhibits like the tach you described in your last post.

firebird310

I HAVE AN 89 FORMULA 350 AND RECENTLY HAD THE EXACT SAME PROB. THE PROB WAS 4 OF THE 8 INJECTORS LOST THEIR RESISTANCE AFTER BEING EXPOSED TO HEAT FROM THE ENGINE. FOUND A SET OF ACCELL BRAND INJECTORS 21#hr for $280.00 from jegs. (TOOK ME FOREVER TO FIG THAT ONE OUT LUCKILY THIS IS NOT MY ONLY TRANSP. HOPE THIS HELPS