This had been plaging me for a month. 1 out of 50 starts it cranks but no start. Only happens when I am alone so I cant check fuel nor spark.

that issue mysteriously disappeared thank God.

Now it has morphed into LEAN. I run a WB and it barely runs at 16.0/1 at 55MPH. But when I come to stop I see gauge at 14.7 and moves periodically to 20/1 and back forth. cold start it is OK but once warmed up in closed loop it starves for fuel but runs.

1. replaced F-P with Delphi TPI. no help.
2. replaced FPR diaphragm(Aeromotive) . no help.
3. today in goes fuel filter yet one was installed 8 years ago 40K miles ago. Unlikely that is it.

Both injectors are firing , they OHM OK, but under a brake stand it breaks up lean. poppoppop out ext. does same on 55mph cruise. pop pop I heard faintly a few weeks ago but attributed it to cold air temps and engine not full heat sinked.

thoughts?

 

How does your vacuum look?

 

Earlier datalogs I saw nothin unusual for VAC-MAP. I could not datalog when it was runnin 16/1 so I hurried to mechanic shop. I presumed a pump as had the n start issues. Also I was witnessing 10.5/1 with N20 then dropping to 22/1 to max on my WB so I knew something wrong with fuel or WB. But at idle at his shop it was erratic on FP read and FP bled down with key on engine off more quicky that I have ever seen. also with VAFPR attached to vac line it was less that normal which for me is 11 lbs or 19.5 at WOT(key on it rises to that.

Overall a vac leakwould cause high idle or suddenly higher BLM and that is not the case. I datalog regularly/

 

I'm more interested in what a mechanical gauge reads on the engine.
A valve check so to speak, but it sounds more exh. valve than intake, do the stiff paper test on tailpipes.
Consider a lean miss cyl charge lighting off in the pipes.
Or a bad plug, wire or a gremlin lurking under the diz cap.
&
Would want to verify timing w/ light.

I think you are chasing a mechanical issue here, might just be a small exhaust leak.
Fuel pump wiring, grounds or such, maybe even a fuel leak within the tank.

 

yes I hear poppop in pipes in cruise state.


mechanical gauge on Aeromotive FPR shows as above.

Valve check? Heads have about 20K on them and stainless valves.

we had the distributor off and all looks new. I suggested pick up coil as older but mechanic says car would not run if defect ? Coil + module is 7 years old Acell blaster unit in cap 40K. Idles smooth when it is at 14.0/1 on WB gauge

This issue is very intermittant. Car ran fine earlier in day and then suddenly exibited these new symptoms. Idles smooth when it is at 14.0/1 on WB gauge.

thank you...

 

OK, so the erratic fp really bothers me, check that chassis ground on frame top back by the tank, when all is OK & if problem remains fill the tank to see if it stabilizes.

Intermittent/incomplete failure of of primary Ing. components sound very plausible to me. First replace your module w/GM #369 piece, it is known to be the best bet part available so you want one anyway, check timing afterward in case there is any diff in latency. If your still having problems the pickup may be trippin out just whenever it feels like it.

Again ANY faulty ground throughout the vehicle will PO the system.