2002 GMC Sonoma 4.3 V-6 Codes

[DreamMachine]

I am looking for some insight into a 2002 GMC Sonoma 4X4 with a 4.3 V-6

Truck came in with a crank no start condition. P0341 and P1637 were the only codes present. I examined the camshaft sensor and found that the distributor as well as the sensor were damaged (cracked) replaced with a new distributor assembly and reassembled the parts. Still a crank no start. Checked for codes again, none present. Checked fuel pressure found it to be 48 psi, installed return line shut off valve and rechecked fuel pressure, still 48 psi. Replaced fuel pump and rechecked fuel pressure, pressure now at 60 psi.

Still a crank no start with no codes.

Tried alternative fuel, carb cleaner, still no start. Disconnected exhaust at manifold, still no start. Removed valve cover and checked number one rocker arms at TDC and both valves closed. Attached timing light to number one and checked ignition pulse, dead on TDC.

Everything points to injector assembly except the failure to fire with alternative fuel supply. I am really scratching my head here....

Got any ideas that I haven't tried?

[sbebenelli]

Does it have spark?

[DreamMachine]

Yes, I have spark at the plug.

[DreamMachine]

To Date:
Cam/Distributor Replaced
Fuel pump checked, found faulty - replaced, Fuel pressure confirmed at 60 psi
Spark tested at plug, spark plugs removed found to have 3 different brands, replaced all with new, gapped to .060, replace plug wires at the same time
Valve cover removed and physically checked valve position in relation to TDC mark and distributor rotor location
Disconnected exhaust at manifolds to check for obstruction in exhaust - none
Injector Balance test preformed with Scan tool
Currently looking at crank sensor - but no issues found at this time

[sbebenelli]

Does it show RPM on the scan tool while cranking?

[Ruger77]

Agree watch rpm on scanner while cranking, just give the scanner a few seconds to update. Also compression test results? Suspicious that alternative fuel didn't help. I personally have not found very many bad vortec injector assemblies in my career, but maybe it's a "here" thing.

[DreamMachine]

RPM is visible on Scan Tool.
I will run compression test tomorrow and upload results when complete.
There was/is an interesting turn of events that I can not explain...while retesting diode test on injection harness while turning over the engine, it almost sounded like it was trying to "hit" a little. I can't explain why it would do that with injection module disconnected.

[DreamMachine]

Compression Test completed. The results are as follows:

Cyl # 1 = 125 psi
Cyl # 2 = 150 psi
Cyl # 3 = 165 psi
Cyl # 4 = 140 psi
Cyl # 5 = 85 psi
Cyl # 6 = 65 psi

Timing cover removed, cam and crank are in time. Chain does have excessive slack greater than .43 indicated in service manual.

Spark plugs indicated ignition when removed for compression test.

[Tim Martin]

Well, Im looking at the diagnosis and work performed thus far. Are we sure that the injectors are being pulsed? It is possible that the PCM is not commanding injector pulse for a variety of reasons. Could be an input sensor (MAF, TPS, ECT, or even an OS) not reading correctly or even dead and not setting code. Have seen GM's do that. My suggestion is to check all the inputs to the PCM and make sure injectors are being pulsed. While compression test is somewhat erratic, that should not create a no-start.

[92zman]

If you spray a little starting fluid, will it start?