Fuel Issues 1994 VR Commodore

[Chewie82]

Hello all. Before I start I apologise for the long rant. As the title says I'm having some serious fuel issues that I'm hoping I might be able to get some help.

So the problem I'm having is the car idles fine and will drive OK when cold. But once warm it struggles to accelerate under any load. I have replaced almost every part I can think of that has anything to do with Fuel, Spark etc. But when running on LPG I have no issues at all so I'm leaning towards a fuel delivery issue. car will bog down and not rev over 1500-2000 rpm but if I leave my foot down it will jump between 1500-2000 and has a flat spot. And kind of sounds like its missing on every cylinder. Doesn't matter if I lightly press pedal it still bogs down and can almost feel like its going to stall. Have used the paper clip trick and only code I get is #56 - Runs Lean Under Load. Car has been to three mechanics and they have all either not had the issue or couldn't figure out what the problem is

Here is a list of replaced parts.

CAS
TPS
IAC
DFI Module
3 X Coil Packs
Spark Plugs (Twice)
Leads
Oil Pressure Switch (not new but known to be good and working - was in a running car with no problems)
Fuel Pressure Reg (Twice) - Fuel pressure test indicated it was faulty from new (not so sure now)
Fuel Pump
Fuel Filters (4 Times) to make sure system was clean
PCM Module
Injectors and Rail have been removed and cleaned (Not professionally)
But injectors seemed to spray all the same and have new seals and filters installed.

I have done resistance and voltage tests on all parts and are all within specs (going from Workshop Manual)

I have performed a fuel pressure test while driving and the gauge pressure drops to around 10-20psi under hard throttle. But while idling and removing and attaching Pressure Reg Vac hose and following Manual Instructions pressure is pretty much perfect. I'm thinking I've possibly dot a dud fuel pump (although I can hear the pump buzzing in the tank). One thing I was leaning toward is the Fuel Pulsation Damper (Under the throttle Linkage) so I bypassed it and it made no difference so weather or not its required it didn't run any better. But cannot find any info on it.

Leaning towards injectors or fuel pump. As car is dual fuel and runs fine on LPG. Apart from stalling when put into park. But that's another issue.

Any Help would be greatly appreciated.

 

[Not_An_Abba_Fan]

The only thing that hasn't actually been replaced are the injectors. I'd be finding a known working set if you can, and fit them and see what happens.

 

[BottleFedVS]

Try a fuel pressure test when it is having the issue when it is warm as the fuel pump may be having issues when it has been running a while.

I hope that helps.

 

[Chewie82]

Thanks guys. Will try your suggestions. You are correct NotAnAbbaFan. They haven't been replaced. I have checked them for their resistances and all were very similar. But you might be right.

 

[Jxfwsf]

Got another MAP sensor to try? (Black rectangle object on the passenger side firewall)
Have you checked the plug and wiring on it?
How is the hose from it to the throttle body? Tight fit both ends and not perished at all.

Regarding the injectors, measuring the resistance only shows the coil is ok, not the rest of the moving mechanical parts inside it (which aren't serviceable)

 

[Chewie82]

Jxfwsf MAP sensor also brand new (less than six months old). ATM I am thinking either fuel pump ( can get replacement as it's still under warranty).Or it's the injectors. Ive been doing the ring around for pricing on reco injectors. The fact that the car is dual fuel and drives fine on LPG means sensors are working. It's definitely a petrol delivery issue.

 

[Jxfwsf]

Only picked that as it wasn't in the list of things.
Guessing it's not vapour injection lpg being an older car. If it's an old mixer converter style at most it'll use is o2 and tps for inputs, and probably not accurately enough to affect it, maybe it's a faulty new part that's already been replaced?

 

[Chewie82]

All good mate. Thinking either. Fuel pump or injectors. This all started after getting a bad batch of fuel. So I'd say injectors are stuffed. Seeing as they are the only part of the petrol system that's not been replaced. Pump was replaced a with a Fuelmeiser brand.

 

[Chewie82]

And no. Not vapour injection. But mixer is good. (I think). Don't have access to a good set of injectors. But I'll hunt around for a set of reco ones. Cheers for your suggestions

 

[Chewie82]

Well changed injectors. Not a brand new set or recos but a reasonable looking set from the wreckers. Problem still there. Would think that of all the cars at the wreckers that I'd pull off a set that are exactly the same as what I originally had is unlikely. Read the codes still getting #56 - Runs Lean Under Load. So it's fuel filter or pump. Because other than fuel lines. Every part of the petrol system has been changed. Including filters and pump.