Also posted this under general tech

Help!!!
87 Camaro 305 Tpi.

Problem started several months ago when stuck in a traffic jam, idled fine, but on pulling forward in traffic it started to stumble, which went away when I opened throttle more. This disappeared when I got out of the traffic. Car ran fine for several weeks after.

Stuck in a 2 hour jam then, problem the same but worse due to severity of the jam, but was fine later in day on return journey, and no problems for several weeks since.

Recently it started to play up more in shorter jams, same thing. Then it progressed to ‘stumbling’ at small throttle openings on the motorway (after a big jam), and then started to ‘stumble’ as I went over big bumps in the road.

This then developed to the car stalling over smaller bumps in road (or running very poorly – 400rpm & picking up again) or stalling when pulling away from standstill.

It has now got so bad that it dies over almost any bump or when selecting drive. It will only be a problem when the engine is warm, from cold (mornings) it will run fine for the first 10 mins, then play up. Less if later in the day.

It will usually re-start immediately with no problems??
No trouble codes are being stored.
It will idle absolutely fine, and rev fine, but die under load/bumps.

It now does not always re-start, battery seems to drain fast (too fast?) but has good voltage.

I have checked all that I know/can as listed below.

New dizzy cap & rotor & coil.
Checked fuel pressure – 38Psi at cranking, 45 Psi at idle, jumps to 60 Psi after it stalls.
Checked all connections on loom (that I can see).
Wiggled all wires that I can see.
Checked charging system, 12.5v at rest, 14.7v at idle, 13.6v with heated rear window & headlamps on at idle.
Checked for 12v at coil when stumbling or cutting out, it has voltage.
Checked magnetic pickups in dizzy, all seem strong.
Checked resistance in pickup coil, all in spec.
Checked all voltages on dizzy/coil loom connections, all in spec.
Checked for 12v on injectors while cranking (would not start) and it had a steady LED lit up.
Checked for sparks from coil HT lead (with induction strobe lamp) under cranking (but wouldn’t start) conditions, and it was getting a stream of pulses.
Checked for spark on No1 while driving (with induction strobe lamp) when it was stumbling, and it was still getting a pulse.
Checked ECM connections, all seemed ok.
IAC unit is functioning correctly, raised rpm & drops off again after 10 secs or so running.
EGR valve is (I think) operating ok, as it does not function below 900rpm, and it stalls at less than that when selecting drive.
Tried tapping block by knock sensor, does not cause problems.

When it stumbles on M/way, it rocks the car against the rear diff gears, so is quite harsh, so I don’t think it is a fuel fault?? As this is usually a ‘softer’ stumble.

My gut feeling is its ignition, but it all appears to be working fine in tests, it will idle all day no problem, and will rev fine no problem, just dies over bumps or when selecting drive (but not always reverse?????)

Heeeeeeelp!!!!!!

 

I'd look at the TPS, and the MAP/MAF, whichever its equipped with.

 

Maybe have someting to do with transmission, like the torque converter?

 

I checked the TPS (forgot to add that one) its .54v at idle rising smoothly to 4.8v at WOT.
Not checked the MAF, but it would trigger a code if it was defective? ( I checked the connections to it & wiggled its wires - no problems)
Julie,
Dont think its a trans problem ( I did check all the shifter switches as well) as there is only the convertor lockup electrics on it.

 

The MAF could still be an issue and not set a code. With the car running trying tapping on it and see if that changes the rpm.

 

Since it dies going over bumps it sounds like a classic MAF failure.

Tap on it while the engine is running and see if it stumbles or the timing changes. Also *IF* you can try starting and driving the car with the MAF unplugged and see if hte problem goes away. I say IF because some will run without it and some won't. Mine never would run without the MAF.

 

Tried it with the maf disconnected, had to play with the throttle pedal to keep it running, but it still died when putting it into drive.

Just added,
Had it up on stands and played around underneath with wiring, all to no avail.
It stalled again when put into drive and refused to restart.
Had a plug out and it still sparked when cranking - might be a weak spark? - no way to tell?
Had an led in the injectors, pulsed while cranking, so injectors working too.
Fuel vapour was pouring from exhaust at this point, so it was flooded (even though I had foot to floor, which should cut off injectors).
So it has fuel (too much) and a spark, so why wont it run?

 

Well it seems to be the fuel pump, finally got it to stall on demand by gently bouncing the rear of the car about 3/4".
Stripped the tank out tonight, but the pump circuits all appear ok???
Very odd.
I've been told that pump failure, even for an instant will kill the engine dead.

 

Usually a pump does just fail. A winding will go bad and it'll get stuck in one spot. Often if that happens you can hit the gas tank and knock it loose and get it running again.

I'd replace the pump.

 

Tried running the pump in a bucket of warm water tonight, left it 20 minutes, all seemed ok???
Tapped it, wiggled wires etc, no problems???
It was running full tilt, very high pressure & volume, but I guess it does not run like this in the car though?
Got a new pump on order, but very worried its not the problem.
How come such a tiny movement on the back of the car kills the engine if its not the pump???

 

Finally found it (after fitting new ignition module) its a wiring loom fault behind the coil area, in the big fat section of loom.
So far (only had quick look) I have found a 1" section of exposed copper wire that links the 3/4 injectors on the right hand bank, so I'm guessing it is grounding the injectors, either shutting them down or causing the ECM to kill the motor to save a short?

 

Re-taped all the loom now and its all running fine :-)