Help: WINALDL Readings & No Fuel Prime & Knocking 350 TBI

[bloe17]

Hey there,

I have a 1991 c1500 5.7l 250k miles. Bone stock.

I just ran WINALDL to help diagnose my knocking engine.

Truck only starts after a long crank once the Oil Pressure Switch kicks on the fuel pump, therefore bypassing the ECM- right?

Truck does NOT prime fuel with key on, engine off. It seems to be knocking, especially at idle. The knocking is present but sounds less evident at higher RPMs. What is very weird, is the knocking was a problem when the prime was working as well. Now it ALSO doesn't prime fuel. So I assumed fuel pump, but my BLM is right at 128 (perfect?) ruling that out. I even removed the injectors from the throttle body, KO to prime and fuel DUMPED down the throttle body, but not a drop flows with injectors in place (ruling out FPR?). I have 12v to each injector wire. I replaced one of the injectors as a test, and nothing changed. This tells me the ECM is not grounding the injectors for some reason? Have tried several aftermarket ICMs, installed a new aftermarket distributor/PU coil which changed nothing as well.

This truck used to have a very notable 2 second whine while priming, now the pump barely makes a whine- but it does whine to a small degree. This made me think the fuel pump is the issue, but why would my BLM be perfect if so? 5v ref, 12v supply, ground wire to fuel pump are all good traced to the ECM/FPR.

Are my MAP levels low? I do have some slight oil leaking from the intake manifold gasket.

ECM is a brand new 1227747 with OEM prom ARJT
No CEL or codes stored

What could this random fluctuation of sensor information mean in my datalog?
Do any of the other readings seem off?

Thanks!

 

[PlayingWithTBI]

It seems to be knocking, especially at idle. The knocking is present but sounds less evident at higher RPMs. What is very weird, is the knocking was a problem when the prime was working as well

Yeah, I don't think the fuel pump has anything to do with your knocking. Take a stethoscope (or a long screwdriver) and see if you can find where the knock is coming from.

but my BLM is right at 128 (perfect?)

Is it running in Closed Loop? BLM won't change until then.

This tells me the ECM is not grounding the injectors for some reason?

Probably - run a continuity test from ECM to the injectors.

Have tried several aftermarket ICMs, installed a new aftermarket distributor/PU coil which changed nothing as well.

Those won't effect the pump's priming. ICM won't do anything for the fuel prime or pressure. The distributor will send DRPs (Distributor Reference Pulses) to the ECM when cranking but, your problem is when you have KOEO. The oil pressure switch will bypass the ECM and turn on the fuel pump.

Here's a link which may help with your troubleshooting;
www.gmt400.com/threads/88-98-service-manuals.43575/

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

 

[Schurkey]

1991 c1500 5.7l

Truck only starts after a long crank once the Oil Pressure Switch kicks on the fuel pump, therefore bypassing the ECM- right?

Truck does NOT prime fuel with key on, engine off.

Fuel pump relay circuit problem. Could be the ECM, the relay, or the wire harness that connects them.

Swapping relays is the easiest test.

It seems to be knocking, especially at idle. The knocking is present but sounds less evident at higher RPMs. What is very weird, is the knocking was a problem when the prime was working as well. Now it ALSO doesn't prime fuel. So I assumed fuel pump,

Failure to prime is not a fuel pump problem. It's a fuel pump power-supply problem related to the fuel pump relay or relay circuit as stated above.

but my BLM is right at 128 (perfect?) ruling that out. I even removed the injectors from the throttle body, KO to prime and fuel DUMPED down the throttle body, but not a drop flows with injectors in place (ruling out FPR?). I have 12v to each injector wire. I replaced one of the injectors as a test, and nothing changed. This tells me the ECM is not grounding the injectors for some reason? Have tried several aftermarket ICMs, installed a new aftermarket distributor/PU coil which changed nothing as well.

The injectors don't spray fuel if the engine isn't providing a cranking RPM signal via the pickup coil and ignition module, and the wire harness connecting the module to the computer. You've replaced the pickup coil and module already with no change. That kinda leaves the harness.

The fact that the fuel pours out of the injector openings when the key is turned from "Off" to "Run" indicates that the fuel pump IS getting a "prime" signal.

This truck used to have a very notable 2 second whine while priming, now the pump barely makes a whine- but it does whine to a small degree. This made me think the fuel pump is the issue, but why would my BLM be perfect if so? 5v ref, 12v supply, ground wire to fuel pump are all good traced to the ECM/FPR.

What is the fuel pressure? Perhaps you're dealing with a failing fuel pump that "works" but doesn't provide enough pressure.

Are my MAP levels low? I do have some slight oil leaking from the intake manifold gasket.

MAP is not low, it's SKY-HIGH. You have nearly atmospheric pressure in the manifold--almost no vacuum at all. Depending on your altitude and weather (barometric pressure) you have maybe one inch of vacuum. IS THE VACUUM HOSE CONNECTED PROPERLY? Doesn't have a hole in it? Not connected to a ported vacuum nipple?

The O2 sensors don't move much according to the voltages listed...but the rich/lean counts are higher than I'd expect. Perhaps a scan-tool anomaly?

What could this random fluctuation of sensor information mean in my datalog?

Scan tool anomaly? Data stream interruption?

I'd be looking for a different scan tool.

Yeah, I don't think the fuel pump has anything to do with your knocking. Take a stethoscope (or a long screwdriver) and see if you can find where the knock is coming from.

Agreed.

Is it running in Closed Loop? BLM won't change until then.

Saying the same thing with different words: BLM doesn't change in open-loop, vehicle has to be in closed-loop for the fuel trim adjustments to activate.

I would have expected the scan tool to show whether the system is in open-loop or closed-loop operation.

 

[PlayingWithTBI]

MAP is not low, it's SKY-HIGH. You have nearly atmospheric pressure in the manifold--almost no vacuum at all. Depending on your altitude and weather (barometric pressure) you have maybe one inch of vacuum. IS THE VACUUM HOSE CONNECTED PROPERLY? Doesn't have a hole in it? Not connected to a ported vacuum nipple?

Keep in mind MAP is the inverse (kinda) of Vacuum. 28 MAP is high vacuum, 100+/- MAP is WOT, depending on atmospheric pressure. His MAP is good for a stock, or mild, cam. My MAP on my "383" with a longer duration (230/236 @ 0.050") is ~54 at idle. When cruising at 60 MPH it actually drops to the low to mid 40s.

 

[Schurkey]

Is his scan tool reporting in inches of mercury, like I expect? Or is it reporting on some other scale, a percentage perhaps?

If it's reporting inches of mercury, he's got nearly atmospheric pressure in the manifold--only about 1 or 2 inches of vacuum, max. 28.x inches of mercury compared to ~30 inches of mercury for barometric pressure; which of course varies with altitude and weather.

I made the assumption (yeah, I know...) that either his engine is running really bad, with the throttle and/or IAC passage open, (sorta-kinda-a-little-bit confirmed by the high idle speed and high TPS voltage) or the hose to the MAP sensor is unhooked/leaking/connected to the wrong port.

But if this is some other scale, then I have no idea.

 

[PlayingWithTBI]

Is his scan tool reporting in inches of mercury, like I expect? Or is it reporting on some other scale, a percentage perhaps?

The Manifold Absolute Pressure sensor is reporting in KPa (KiloPascals). this sensor is looking for pressure, not vacuum where 100 kPa is zero (atmospheric) pressure. Look at your MAP when you turn KOEO, it'll read close to 100 depending on elevation/atmospheric pressure. Here's a conversion chart for MAP KPa to BAR (1 BAR - 14.5 PSI)

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[Schurkey]

The Manifold Absolute Pressure sensor is reporting in KPa (KiloPascals).

OK. NOT reporting in inches of mercury.

this sensor is looking for pressure, not vacuum

Yes, that screws-up a lot of folks.

Look at your MAP when you turn KOEO, it'll read close to 100 depending on elevation/atmospheric pressure.

MY scan tool reports MAP readings as inches of mercury; so when I go KOEO, it's showing barometric pressure of "about" 30 inches of mercury, depending on the weather.