gta_knight

Hi all.

I bought a 91 firebird a few weeks ago. It was running, sounded like it was misfiring slightly so I've ordered lots of service bits to give it a good going over. It threw a code 35 so I ordered a new IAC too.

I went to start the car yesterday to move it and it fired straight up but it runs for like 2 seconds and cuts out. If you hold the throttle down when it starts it makes no difference either.

so it's obviously getting fuel and spark as it does start each time but I can't figure out why it keeps cutting out after it does start?

OrangeBird

iTrader: (1)

If I had to guess , my first check would be the fuel pressure . Get a gauge on the test port on the fuel rail and see what the pressure is while it's starting for two seconds till it dies . My suspicion is that the fuel pump is doing the startup prime just fine but then not running when the engine starts , hence the startup then quickly die symptom .

And , I know you didn't ask about VATS , but , just to put it out there , VATS will not kill a running engine so it's not at all likely to be VATS related .

gta_knight

Thanks man. it looks like the vats has been bypassed as the relay behind the kickpanel is gone.

It had a new fuel pump fitted just earlier this year by the previous owner. he cut the access panel so I've had a look. I will try and get a pressure gauge to see what it's doing then.

If it's not pumping fuel when running then is that some sensor problem not telling the pump to run after start-up?

gta_knight

Ok, some progress. We bypassed the fuel pump relay and it stays running. If you pull the bypass wire out of the connector it keeps on running! And when you switch off, plug the relay back in the car will start up and run again. Really really weird. Im at a loss on this.

it's probably worth mentioning the car still runs really crap. When it first starts the idle is up and down a bit. If you try to rev it then it nearly cuts out and it had a few backfire type pops from the exhaust too. When it warms up a bit it's not as bad. You can rev the engine and it sounds ok but when it comes back down to idle it's still a bit up and down.

I've replaced the IAC valve as it threw a code for that. A code 33, 34 and 35 infact! It's had a new MAP sensor too before I got the car and the old one was in a box in the back still. I found quitea few vacuum leaks too which are sorted but the car still has this weird starting problem and running issues

I still need to get a fuel gauge to check the pressure ideally

gta_knight

Done a fuel pressure test today. Key on and it shoots up to 40psi then immediately starts falling back to zero. But the car still starts right up and runs. Holds a steady 40psi when running. Should be 46 I think?

so I'm thinking maybe the fuel pressure regulator might be bad? I might ohm test the injectors too but for it to leak down so fast it would literally have to pour out.

hmmmmm

luca

i had this once on a mpfi buick
1 injector of 6 got 1 ohm the rest was as it should be around 13ohm
it started ran like 5 sec then died
changed the injectors solved the problem

gta_knight

thing is the car runs now after changing the fuel pump relay. It's had a new pump too. I changed the filter.

It runs pretty bad though. It can be pretty smooth but you rev it and as it comes back down to idle it stumbles and nearly cuts out sometimes then runs rough.

I've also got a code 34 as well. Something vacuum related to the MAP sensor so I need to check for more leaks too

Six_Shooter

iTrader: (2)

base pressure should be 44.5 PSIG, that's fuel pump on, engine not running.

While running, fuel pressure should drop in proportion to vacuum. Typically though at idle you should see down to about 36 to 37 PSIG and rise when you open the throttle.

gta_knight

ok thanks. I need to figure out why mine is falling back to zero then. When it is running it's steady at 40psi. So again possibly the regulator?

gta_knight

Primed the system today then set about changing the plugs, they were all pretty black like the car had been running rich but the plugs were all dry so it's not a stuck open injector.

pulled the intake off and OHM tested the injectors and they are all over the place. Lowest was 12.5 And the highest was 17.8 And all 6 were different.

So that still doesn't explain the sudden pressure drop. I need to clamp the return line and try again to see if it holds pressure then which means the regulator will be ok and it must be this check valve in the pump?

I've got no idea where this check valve is inside the pump assembly though so any info on that would be great

Whitebird75

It sounds like the injectors are going then. I had a similar issue, and I solved it with new injectors and a new fuel filter. Pull the vacuum line that connects to the Fuel Pressure Regulator, and give it a sniff. If it smells like fuel, the regulator needs rebuilt/ replaced. If not, the regulator should be fine.

Also to note, the timing on these cars are a bit different than a small block Chevy. It is best to use the #4 spark plug wire for the timing light signal. Also to note, the #1 spark plug is on the opposite side of the engine than a small block. In the states, that would considered the passenger side. I don't know if you have a left or right hand drive car.

gta_knight

yeah with results like that it's best to just replace all the injectors and not mess around. Left hand drive. That's the good thing about the UK we don't need to convert our cars to right hand drive. We can just leave imports as they are.

I havnt actually checked the timing yet but it's on my list to do after I install the new parts and get it running again.

So you are saying time it from number 4 on the timing gun?? That's a bit weird, would that not screw up the setting totally as it should go from number 1?

Mark RWC

Number 1 is shown above.

RBob

iTrader: (1)

It works, I started to do this to keep from having to drape the timing pickup cable over the engine. Plus it is easier to get too.

RBob.