1997 6,5 TD - injection pump replaced for a mechanical one, PCM problems

[MC775]

Hello everyone!

From several days I'm the owner of 2 doors 1997 Chevrolet Tahoe 4WD powered by 6,5 TD. I bought it broken - previous owner told me that the transmission is broken and the car can only drive at the 1st and reverse gears. After an inspection and some tips from a different forum it turned out that an electronic injection pump in my Tahoe has been replaced with a mechanical one. I've read something about this procedure yesterday, and now my suspection is that the problem is in this modification, not in the transmission itself. Symptoms: MIL light is on, and it seems that car is in a limp mode: it only drives on 1st and reverse gears.

In a shortcut:

1. I pulled out OBD codes, list below.
2. There is a loose bunch o wire harnesses at the top of the engine, probably used for electronic injection pump.
3. There are some modifications made to the big wire harness at the back of the engine, some wires are cut and connected with the wires from loosy harnesses.
4. APP is replaced with a pedal with a cable that goes to the injection pump.
5. Nothing else looks like it was modified.

Today:

1. I re-soldered all modified connections on the big wire harness, old connections were old and rusty.
2. I checked the crank sensor, it has correct impedance.
3. I disconnected plugs from the transmission and cleaned them up, all were rusty.
4. I cleaned some other rusty electric connectors.

Unfortunately it didn't help

I'm looking for some information about this modification, especially about how was the PCM forced to work with mechanical injection pump. In a GM service manual I found that 3 faulty APP sensors will cause PCM to put the car into a limp mode. As you can see at the list of my codes, there are 3 codes for APP. Of course there are no APP sensors in my car since it was modified for mechanical injection pump, so how was the PCM "fooled"?

I will be very grateful with any help from you.

Codes list:

Car Scanner ELM OBD2
DTC report
Selected brand: Chevrolet

============1==============
P0601
Raw code: 0601
ECU: 10
Status: Pending
OBDII: Engine control module (ECM) - memory check sum error

============2==============
P0601
Raw code: 0601
ECU: 10
Status: Confirmed
OBDII: Engine control module (ECM) - memory check sum error

============3==============
U1000
Raw code: D000
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test is inhibited by other DTC, Test has not been completed, Validated fault present at time of request
OBDII: Class 2 Communication Malfunction

============4==============
P1218
Raw code: 1218
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Validated and stored in non volatile memory
OBDII: CID High
Chevrolet: Injection Pump Calibration Circuit

============5==============
P0601
Raw code: 0601
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Engine control module (ECM) - memory check sum error

============6==============
P0228
Raw code: 0228
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Throttle position (TP) sensor C/accelerator pedal position (APP) sensor C - high input

============7==============
P0223
Raw code: 0223
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Throttle position (TP) sensor B/accelerator pedal position (APP) sensor B - high input

============8==============
P0215
Raw code: 0215
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request
OBDII: Fuel shut-off solenoid - circuit malfunction

============9==============
P0122
Raw code: 0122
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Throttle position (TP) switch A/accelerator pedal position (APP) switch A - low input

============10==============
P0601
Raw code: 0601
ECU: 10
Status: Pending
OBDII: Engine control module (ECM) - memory check sum error

============11==============
P0601
Raw code: 0601
ECU: 10
Status: Confirmed
OBDII: Engine control module (ECM) - memory check sum error

============12==============
P0601
Raw code: 0601
ECU: 10
Status: Pending
OBDII: Engine control module (ECM) - memory check sum error

============13==============
P0601
Raw code: 0601
ECU: 10
Status: Confirmed
OBDII: Engine control module (ECM) - memory check sum error

 

[smdk2500]

I don't know much about the DS4 to DB2 pump swap but I do know you have to get a transmission controller for the trans to operate properly. Try this site there is a guide for converting to the db2 pump. http://www.mediafire.com/?4wj51rn22o6z6

 

[MC775]

Thank you for the answer! Could you please tell me how was the transmission controlled by default? By PCM or another controller? If it was a different controller, where was it originally located? I've seen that author of the guide you have attached recommends using GM 16196390 trans controller and putting it next to the PCM, behind the glove box. However, in my car there is only PCM and VSSB behind the glove box. I'm sure this car was roadworthy and it has all components it needs, but I have to localize and check them.

 

[smdk2500]

On the 92-93 trucks the trans had a trans controller. It did not have anything for the engine. If I remember correctly it was located behind the glove box as well. On yours when new would have been controlled by the PCM.

 

[MC775]

OK, I did some more research and inspection on the car and I got lost a bit in this mess of wires. I have 3 accelerator pedal OBD2 errors, obviously I don't have APP because it was replaced with the cable. I think those 3 errors put the car in the limp mode, that is what service manual states. Throttle position sensor plug on mechanical injection pump is disconnected, and there is no other plug to connect it to. However, crankshaft position sensor is OK (I checked its resistance) and its wires are soldered to the engine wire harness. Looks like car has modified electronics for mechanical IP but I can't find any additional controller for the transmission. Behind the glove box there is only PCM and VSSB. The only idea I have is that standalone transmission controller is installed somewhere around the transmission, under the car, unfortunately I don't have an access to vehicle lift to check it now, next week I must go to the friends workshop to look at it.

I'm looking for any information about this mod, looks like it was not made with Bobby Martin method, so I have completely no idea how to deal wit it.

 

[MC775]

After a long time of studying service manuals to understand how the original system worked and some searching on the Internet I have an update. Maybe it will be helpful for someone in future. First of all, I've inspected my car and there is no standalone trans controller for sure. Then, I found this thread on the other forum:

DB2 Retrofit Mechanical Injector Pump in '98

www.dieselplace.com

A man had exactly the same case as mine, so I tried his method to connect TPS directly to the APP2 circuit. Unfortunately it doesn't work for me. Yes, APP2 OBD code (P0223 "Throttle position (TP) sensor B/accelerator pedal position (APP) sensor B - high input") disappears from the computer, but car is still in the limp mode. I've get a freeze frame that says something about a bad voltage in APP2 circuit. I checked it out in the service manual, and yes - OBD is right, APP2 circuit voltage is 4,5v (idle) to 1,5v (WOT) while TPP is 0,50v (idle) - 4,75v (WOT). So not only the voltage range is not correct, but also the way those sensors work. APP2 decreases voltage while depressing pedal, TPP increases it. I don't know how did it work for the guy from the other forum.

But there is also a light at the end of the tunnel. I found that APP1 sensor works the same way as the TPS, so it increases voltage while depressing pedal. Nice, but still there is a difference in voltage range, APP1 works between 0,74v - 3,7v. So my next step will by a try to adjust TPP sensor on my IP pump, i think it can give 0,74v at idle because there is some room on adjustment screws. Maybe 0,74v will be enough to get the car out of the limp mode. If not, I think I'll have to look for standalone trans controller.

If someone can share some tips for me, I will be very grateful. Cheers, have a nice weekend!