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96 suburban 6.5 timing control

turboaudi said:
the funny thing is i have 2 trucks doing almost the same thing the other one likes doing it going down the road it scares the hell out of you
Click to expand...
Figure out what the commonality between the two trucks is, and you might be a long way to solving your problem.:cool:
You might agree the ECU is not it. Since you have swapped it with another that has different SW that gives essentially the same symptoms :thumbsup:
 
ok i swapped in a crank sensor still does it scan data all looks good fuel press ok i swapped the engine harness [under the intake] still doing it i will probably pull the ip next week does any one on here rebuild these pumps ? what are the signs of low transfer pump press ? fuel sol incorrectly adjusted ? what else could mess with timing control in the ip? thanks dave
 
i changed out the ip today after doing tdco i drove it 2 or 3 mi it started acting up again ! i have checked the harness under the int & the pinouts on the ecm swapped diff ecm all scan data looks ok the actual timing will set at 3 or4 deg when desired is 7 or 8 deg then it will go to 20-25 deg & repeat several times the stepper motor is moving trying to set timing then it will be ok act &des will be the same there isnt much left i may try to drop the tank & blow out the lines maybe the return is restricted ? i also pulled the ip down everything looks new f sol was 5 thou adv piston was free & like new this sob is going to the scrap yard if they will let me run the crusher !!!
 
i hooked up a press gauge fuel press is above 3 psi wide open it also when i floor it the timing will drop to 3 or 4 degrees it is a dog when the timing is advanced 18 - 20 deg & i floor it it runs great black smoke & all so i dont see a fuel delivery problem the pump was on one of my other trucks it is a known good pump it does the same thing as the other pump i also added extra grounds i am going to check ecm wiring again dave
 
Wow its nice having a known pump to eliminate that as an issue. Are we sure its not the PCM? Maybe try putting the PCM that the pump was originally with in this truck. Maybe test the PCM's in another truck? This is confusing.:???:
 
When you say actual timing, is it labeled actual timing on the scanner? Or is there another option for injection pump timing, or measured timing.

On the OBD1 there is the desired and measured timing, which should be the same value. And Actual Injection Pump Timing is a whole different kind of reading. On CarCode for OBD2 I have seen it is just labeled Injection Pump Timing Desired and Injection Pump Timing.

What is your input fuel pressure and where did you get the IP's from? You can try loosening the transfer pump relief screw which is in the lower IP inlet fitting.

What is your TDCO set at?
 
i am using a mastertech that has gm software (i worked at gm dio all diesel engs ) it shows actual & desired timing tdc offset is -1.45 i put another crank sensor in it the tdco went to -2.45 i set it to - 1.30 when i drove it home timing stayed at 4 deg while desired was at 12-14 deg the pump is off a truck i bought for parts it was rebuilt in 2011 it worked perfect in the other truck input fuel press is 3-8 psi i moved the transfer pump relief screw both ways 3 diff ecms the crazy part is i have 2 trucks doing this
 
Did you try checking the wiring for continuity, shorts between wires and shorts to ground, from the stepper motor to the PCM?

Unplug both ends and check for shorts between each wire at the stepper motor, then each wire to ground. then you can jumper two of the wires together on either end with a paperclip or something like that to check for continuity across the two corresponding sockets on the other end. Do that until all wires are verified good. For continuity there should be less than 1 ohm resistance for each wire. A short would be any resistance existing between two of the wires, where it should be an open circuit with the meter showing Overload or OL or something like that.

Some of the wiring was different between years of OBDII trucks, so if none of the PCMs are originally from a 96 that may explain it. I can check the pinouts of the stepper motor at the PCM later from 96 to later trucks.
 
ok i did some tests today then it would not advance from base timing so i took the stepper motor off & tried to run the timing manually . the advance piston valve would not move ! i pulled the pump took the adv piston out the valve in the center was stuck so bad i couldnt get it out i had another one so i cleaned it & installed it it works perfectly now. this is my suburban my pickup is next it is doing the same thing with a new inj pump i will probably change the crank sensor first it has 300k on it so one is fixed i also have 96 97 98 c/k factory shop manuals thanks for the help dave
 
What do you think caused this problem do begin with?

Also how does a new "Rebuilt" IP have this issue from the get go?

Nuther words, "What the hell happened?"
 
maybe someone ran some gas through it and then let it set when it stopped running, the rebuilt doesnt make sense unless it came from sketchy source.
 
i pulled the adv piston out & cleaned it before i put the pump on maybe the pump had dirt in it ? i am going to change the fuel filter & flush the line to pump just in case dave
 
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