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96 GM suburvan 6.5 Turbo diesel. Crank, hardly starts one second and shuts off

  • guafa
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03 Mar 2019 12:07 #27550 by guafa
Hi there,
Does anyone have known good waveforms for this car?

A friend of mine is becoming crazy with this car, which received from another workshop (which rebuilt the engine).

After rebuilt engine, the guys of first workshop couldn't turn the engine on. They teared down the engine twice to check.

When my friend received it, first checked timing (physical marks in gears), then changed PMD (the circuit in charge of turn on and off solenoid which controls injection pulse width), then changed fuel injection pump, then thought in replace PCM but first asked for my opinion.

I checked first CKP signal, which is sending a pulse every 90 degrees of crankshaft revolution to the PCM (every square pulse with same width).

Then i checked CAM signal. reluctor wheel
is located inside fuel injection pump. There are two signals. High resolution signal with 512 pulses in just one revolution and CAM signal with eight pulses in one revolution of camshaft (one of those wider, indicating TDC of cilynder number one). These two signals (high res.and CAM) are stamped in the same disk, which means they can't be desynchronized.

On the other hand, i don't know how CKP and CAM signals should be synchronized (at the moment, they don't raise at the same time).

Other tests.
1. Due to fuel solenoid in injection pump controls not only injection time but previous charge of fuel in injection chambers, i connected 12 volts directly in fuel solenoid, which forces to inject the complete fuel charge. The engine turned on very acelerated, ran one second and then turned off.

2. I advanced fuel injection pump gear one teeth. Intead of hardly start, the engine started inmediately one second but still turned off.

Thanks in advance.

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03 Mar 2019 18:30 #27569 by Scannerfanner
Is the fuel pump running? At correct pressure? How about coolant temperature sender and manifold air temp sensor, are they giving proper feedback? I don’t have any experience with this engine, just shooting from the hip....

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03 Mar 2019 20:43 - 03 Mar 2019 20:53 #27573 by guafa
Is fuel pump running at correct pressure?
Injection pump has two stages. transfer pressure (first stage) is ok (0 -160 psi depending of engine speed (40 psi when cranking)). Injection pressure not measured, but nozzle spraying in the air looks good.
Lift pump pressure (inlet of injection pump) is 18 psi.

ECT and IAT feedback?
We simulated with resistors, diferent ECT voltages. PCM responded with diferent pulse width. That is the reason i guess PCM is good.

We also took control of injection width, by programing a microcontroller, which detects injecton event and then activates fuel solenoid with a new pulse width controlled by a potenciometer (same result as earlier)

Thanks.
Last edit: 03 Mar 2019 20:53 by guafa.

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12 Mar 2019 13:08 - 12 Mar 2019 13:12 #27769 by diagDOG
Is the ECU trying to fire injectors when car cuts out?
Last edit: 12 Mar 2019 13:12 by diagDOG.

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12 Mar 2019 13:55 #27770 by guafa
Hi diagDog. I would say yes, but willing to probe deepper your question.

When i see recorded data in scope, i can notice PCM trying to keep engine running, by changing pulse width.

Any idea to know exactly when engine collapse and when PCM stops injection pulses?

Maybe by watching any change in frecuency in CKP?

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