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Discussion Starter #1
Hi everyone.

I'm new in forum and also in diesel engines (i have 10 year experience in gasoline engines).

A friend of mine (auto technician), came to me with a 96 OBD2 engine rebuilt 6.5 Suburban TD (i'm guessing is the only one in my country).

The truck owner has 4 stanadyne 5521 IP's and 4 or 5 PMD's. Non of them starts the engine for more than 3 seconds.

Since i have checked more than 180 rpm at cranking, more than 10 volts in battery while cranking, all glow plugs heating when i power them with battery directly, current drain during glow plugs activation, no air bubbles in fuel lines, 12 psi in lift pump, good compression, correct firing order, injectors shooting in the air. My next direction is to check injection timing. Am i missing something?)

I have scope CKP(1), CMP(2) and high resolution signal(3) wave forms.

(1)Power CKP is steady at 5volts, ground is getting pcm and signal is negative pulse (all the time 5volts and falls to 0v at TDC). All back probed in pcm connector.

(2)Power CMP (inside IP) is steady at 5 volts, ground is getting pcm and signal is positive pulse (all the time 0 volts and rising to 5 volts when is suppose optical sensor gets TDC of every cylinder. TDC of cylinder #1 pulse is about 3 times wider than others. All back probed in pcm connector.

(3)Same story. 512 pulses from 0 to 5 volts.

Here is the issue. I have seen CKP and CMP signals are not in phase. I mean, they are not triggering at the same time.

* Is that normal?
* Do any of you guys have a known good wave form?
* Is this know good wave form in iATN database?

When engine starts for 3 seconds, it rise to 1450 rpm aprox. (Measured in scope and scanner datastream). At that point, pcm cuts fuel control solenoid signal.

*Is pcm protecting engine for over speed?
*Is pcm protecting engine from ckp/cmp misalignement?

Please let me know your comments. Thanks in advance.
 

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Discussion Starter #2
I forgot to mention there is a P1643B dtc (related to pwm circuit). I am not sure about this code, since my scanner is not original gm, but it reads 5 datastream.

Supposing the code is true, what does it mean? (In this diesel engine/pcm)
 

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Code 1643 is from a 1997-up diesel, WTS lamp circuit problem.
1996 does not have that code, circuit functions differently.
A 98-up diesel will have your same problem if security is triggered.
The PCM lets the engine start then immediately shuts off injection.
Has the engine run with that PCM (the computer)?
Have you tried to start it with the OS unplugged?
 

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Discussion Starter #4
Thanks for your prompt response.

I have confirmed year vin number ("T" letter). So maybe my scanner in lying.

I tried with OS unplugged, same thing.

The only clue i have about PCM, is the sticker number (please see attached pictures).

*How did you know 96 year doesn't have that code?
*Can you direct me to that kind of info? I mean service bulletins, TBS, everything related to how this pcm works. Thanks.

What are those security conditions that triggers pcm?

Service manual says ckp pulse match one to one with cmp pulse.
Does it mean one cmp pulse per one ckp pulse (counting) or (counting + trigger timing)?

Thanks in advance again
 

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Lots of info here, see the FSM's.


https://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/53309-6-5l-faq-s-master-list-information-6-5-answers.html


I know these diesels inside and out and am kinda familiar with the electrical.
The 96 does not have that code because the WTS lamp circuit is different than the 97-up trucks. The PCM does not turn on the WTS lamp on a pre-97, so no code to set, the programing is not there.
Since you are getting that code it must be a 97-up code.
FYI the 96 thru 2002 OBD2 diesel PCM's are the same, the difference is the programing.
Using a 98-up program on a 96 or 97 requires the security be turned off at the PCM, the other components needed for it to work are not there.
Try unplugging the OPS, fuel heater, WIF and main transmission connectors and see if things change. A problem with those items can cause the PCM to trip out.
 

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Discussion Starter #6
Ok Thanks. I'm going deeper about OPS, WIF and transmission conectors and then let you know.


About PCM, I'm seeing two options. PCM was swapped and security features are still active (because p1643 code showing up) or scanner is lying me (i have tried two diferent generic scanner brands). I gonna try to get a tech 2 scanner.

Cheers.

P.S. please keep an eye on my earlier questions. Thanks
 

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What is happening to the engine, is exactly what happens when the security system disables the engine. Starts for a few seconds then shuts off.
Is the security light on or flashing after engine starts?
 

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Has the burb ever run correctly with the PCM you have?
A 96 does not have a SECURITY lamp.
 

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Discussion Starter #9
Hi guys. Update of today.

Oil pressure switch signal (D5 pin at pcm) is working as it should. 12 volts during key on for the first 10 seconds (due to lift pump relay activation). Then 12 volts when cranking (i suppose due to oil pressure).

Today i confirmed with owner he has never changed pcm and it was working properly (which drives me to think scanners are lying to me).

I tried with transmission, water in fuel and oil pressure switch connectors unplugged. Nothing changed. OPS is new.

I checked fuel heater resistance. It's more thank 100kohm (it's pretty high, isn't it?). Anyway, i think it is necessary only for winter? Average ambient temperature here is about 24 celcius (75 fahrenheit).

Something weard i found, is fuel heater connectors has 3 wires. Black (a), pink (c) and yellow/black (b). (a) & (c) are shown in service manual (power and ground). (b) is not in service manual. That wire is connected to ground. Is this a signal and is shorted to ground?

I checked for fuel temperature (thermistor inside IP). Voltage is about 4.2 volts (C8/C1 pins).

I checked also MAP sensor. Voltage is about 1.98 volts (baro pressure here is 82 kpa/24.2in/hg).
 

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Discussion Starter #10
About your questions. Thanks.

*No warning lights on the dash.

*If i let the air heats through glow plugs before cranking, it starts with huge energy and three seconds later, it dies. If i crank it immediately (no time for glow plugs to heat), it delays one second to start, then starts with less energy for three seconds and dies.
 

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The fuel heater has 2 wires, the water in fuel (WIF) sensor has 3 wires.
The PNKs are 12v. ign, the BLKs are grounds, the YEL/BLK goes to the WIF lamp in the gauge cluster. The heater is self controlling, you can leave it unplugged, WIF also.
I would be trying a different PCM at this point.
 

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Discussion Starter #12
Ok i got it. Thank you, i was confused about wif and fuel heater. That means that yelow/black wire is not shorted to ground, but the wif lamp is showing low resistance because of the bulb. Anyway, heater and wif don't have feedback to pcm, then they cannot cut off fuel control signal.

About pcm, i have simulated diferent coolant temp, by changing resistance and pulse width changes. It is controlling lift pump and fuel contro solenoid. It is also comunicating with scanners and giving me feedback (datastream).

I'd really love to have those known good wave forms (ckp vs cmp) before rule out pcm. What do you think guys?

The owner bought IP's, PMD's, rebuilt engine. So i want to be as sure as i can.
 

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One of the first things you do when chasing gremlins is to decapitate as many of the devils hiding places as possible. You need to UN-PLUG all the none essentials that could be feeding back to the ECM. Unplug the temp sensor, the OPS, the crank sensor, wastegate solenoid, any other temp sensor device. DO NOT unplug the Optic sensor.
Hot wire the fuel supply pump. The engine will be slow to crank without the crank sensor but should start. You will throw a lot of codes. If this works start plugging the devices back in.
>Guess crank sensor, even new ones throw a bad signal. Use only AC Delco as the after market units are not compatible with the diesel as most people have found out the hard way.

Here's thread similar to yours where I correctly identified the problem at #61 in a very long thread. https://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/906129-1994-blazer-starts-stalls-after-5-6-seconds.html
 

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Discussion Starter #14
Hello guys, long delay to reply. I was on hollydays.

I unplugged ckp sensor, ect,iat, wastegate and after 5 or 6 seconds of cranking time, engine started for the same 2 or three seconds.

I found that pcm ground (back probe at pcm connector), rised up to 400 mv while cranking (which for a gasoline engine is to much). Then i wired with another ground directly to battery (-). Now ground voltage rised up to only 100 mv, but i didn't change anything.

I unplugged all injector lines (high pressure ones) but leaving only one at a time to confirm any combustion stroke is doing the job and in fact, all they are.

I picked up scope signals for CKP and fuel control solenoid, confirming again that pcm is cutting fuel control signal at 1500 rpm, while is still receiving CKP signal (AC Delco coming, just to discard current generic brand).

*Is it normal these engines start at that speed?

I found also fuel control solenoid driver, is like a peak and hold injector driver (in gasoline engine). It triggers injector with a high voltage (to move the pintle) and after few milliseconds (let's say 2 ms) it keeps the pintle active with a low voltage (about 1.6 volts).

*Can someone confirm this?

I finally tried to start engine with only four cylinders plugged. Same thing. Engine dies after start.

I recorded a crank/no start video and also ckp vs FCS signal. In a second reply, i'm going to post them.

Thanks.
 
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