Heres a kicker

[Shannonwilkerson]

Hey guys.
1995 c2500 5.7/nv4500
Running decent at idle, slight surge causing +-200 rpm fluctuations. When im driving at all, it bogs then picks up and goes, bogs then picks back up.
I have code 42 and 52. No I don't have an actual scanner because I used the last of my savings buying books for school.
Timing has been verified at 0* by timing light with the wire behind glovebox unplugged.
Pickup coil in the dist went out. It is new as of a few months ago. It's a delphi unit. So is the coil.
Wires are new. Replaced due to arcing. Plugs are also new.
I really would hate the idea of a brand new dizzy being bad.
What do you guys think

 

[xmanjeff]

sounds like fuel to me

 

[Kira]

Look at this:

How many miles on your vehicle....ever tried Techron?.....

 

[SC Maintenance]

Wow - its been a while...

Code 42 is the ignition bypass. It allows the ECU to go from base timing to computer controlled timing based on the other sensor inputs.

Code 52 is an issue with the California Emissions module. Back then CA emissions wasn't on all cars, and GM came up with a plug in module to modify from standard to CA emissions. Its not sensing the plug in module for some reason.

These two are possibly tied together - the CA emissions may not allow the timing bypass or vice versa. LIke I said, its been a while, so I am not sure how this helps you other than it appears to be electical issues, and you likely want to start by checking wiring and grounds and maybe even re-seat the Emissions module, etc.

 

[Shannonwilkerson]

@xmanjeff fuel pressure is at 12 psi. Which is spec for tbi.
@kirai have a kit coming for the throttle body. With only 140,000 miles on it at 28 years old I bet the diaphragm and gaskets in the tbi unit are crispy.

@SC Maintenance your response baffles me (not being an jerk I'm actually intrigued)
It baffles me because, this is a federal emissions truck. It has always been a mississippi truck. It dosent even have the A.I.R. pump that the California trucks had.

 

[jhellwig]

I read a few years ago about issues with the magnet assembly swelling due to rust causing timing issues. I think people were also saying new distributors were hit and miss even on the delphi ones.

 

[SC Maintenance]

@xmanjeff fuel pressure is at 12 psi. Which is spec for tbi.
@kirai have a kit coming for the throttle body. With only 140,000 miles on it at 28 years old I bet the diaphragm and gaskets in the tbi unit are crispy.

@SC Maintenance your response baffles me (not being an jerk I'm actually intrigued)
It baffles me because, this is a federal emissions truck. It has always been a mississippi truck. It dosent even have the A.I.R. pump that the California trucks had.

I am not claiming I understand it either, but there is a module that adjusts the ECU tune / timing based on the emissions settings for the vehicle, and your ECU can't see that module - that is what code 52 means. It has to have a module in their whether its CA emissions or not. Why they call it that is beyond me, but it needs a module in that port, and whatever is in there now it can't see. The ones I have seen look sort of like a memory DIMM slot except instead of a circuit board type card its a big fat thing that snaps in with clips on both ends. =

So take this for what its worth - I am no expert - if it were my rig I would pull the ECU out from under the dash, open that port, make sure I grounded myself then make sure that module is tight into that port and hasn't popped out somehow. you may want to even pull it out and check for corrosion, etc. But be careful - your messing with 30 year old electronics. Or you can find someone smarter than me on this stuff, because I worked on these cars - or more specifically helped work on them - when they were new. Haven't touched one in 25 years or so?

 

[joegreen]

You should go ask on gearhead-efi.com they are one of my main sources for tbi information. There are some very educated people there on the tbi system.

 

[Shannonwilkerson]

@SC Maintenance sorry if I came off as an ******e man. Hope I didn't! I'm just annoyed that it's one issue after another with this thing. But when it runs good I can pull the earth with it!
I believe you're talking about the PROM module that plugs into a port on the front of the ecm it's self. Will definitely check!

 

[Shannonwilkerson]

Update:
Finally got a little time between school, work, and my family to look closer. The ecm wasn't put back in its holder my the previous owner. It was just sitting behind the glove compartment and flopped around going down the road.
I put it back in its holder and all has been well for about 2 weeks. I've been driving it to work since I'm on Xmas break from school. Work is a 45 minute drive 1 way.
No more issues.

Now I just have to change the fluid in that nv4500. I will be using redling mt85.



This truck has almost drove me to drinking, but it's a labor of love. This truck is freaking awesome now that it runs right. **** thing is a stump puller lol