89 Jimmy Surges at high rpm

[Mav2u]

The Jimmy is surging especially when I shift it into 2nd gear and run in around 2000 to 2500 rpm. If I hold the speed steady it gets a slow surge in the forward motion of the truck. I don't hear the engine surge or the rpm just the vehicle, sort of like hitting a bunch of small puddles one after the other on the road making the truck slow for a second and then regain speed again. I also noticed that it sort of sounds like it is back firing or missing internally in the engine at a little higher rpm in 2nd.

A little history on the truck:
New plugs, wires, cap and rotor a couple months ago
rebuilt fuel pressure regulator, fuel pump, and fuel filter

New tranny 2 years ago and 25,000 miles ago, GM brand new 700R4 with newly rebuilt 10 bolt rear with gov/loc and 3.73 gears.


Also when cruising at highway speeds around 70 mph the truck seems to have a problem staying at speed. I have to nudge the peddle up a little more to keep it at the constant speed, almost like the truck is dragging or having trouble holding the power needed to keep the truck going.

I'm not sure if this is a transmission problem or fuel/ignition area. Any help and ideas would be appreciated to get the beast up to par again. I'm at a loss and wits end.

 

[Thunder]

Might possibly be your magnetic pick up coil in the dist going bad. They will cause a light miss at mid rpms when the engine is under a load if they are going out.

Check your trouble codes. pick up coils will throw a code 42.
Or put an ohm meeter on the wires that come off the pick up coil. Resistance should be between 500-1500 ohms. Replace the unit if out of those specs.

 

[Can Can]

You might also want to check that your catalytic converter isn't plugged. Lack of power can also be caused by a restriction in the exhaust, which can easily happen when a catalytic converter slef destructs internally.

 

[Mav2u]

I have change the pickup control module but not the actual piece that is on the shaft. Do you need to change that also? I didn't realize that it would wear down also. Upon looking in my Helm's book it has a troubleshooting guide for it I think so I'll try that out.

Catalytic converter has been changed to a performance one 3 years ago with the exhaust system.

Items I've changed in the last 2 years list:

• Spark plugs bosch platinum
• pickup control module
• Plug wires MSD 8mm
• Ignition coil
• cap/rotor
• map sensor
• throttle position sensor
• EGR valve
• Idle air control valve
• throttle cable
• 700R4 Transmission ( New GM crate from dealership )
• Alternator
• water pump
• radiator
• fuel pump
• rebuilt fuel pressure regulator
• New boyce 3.73 gm 10bolt 28 spline gov/loc'd rearend
• new 3.73 gear in front rebuilt hub to hub

and that's all that I can think of off the top of my head. I've been systematically going around and changing everything when I get the cash or I have to. Most of the sensors I change before they fail that way I have a working old spare to keep for backup in the trucks repair box.


appreciate the help
Mav

 

[Grim-Reaper]

My 88 454 burb was doing that. Vacuum leak at the base of the throttle body and cracks in the plastic vacuum lines were the cause. The EGR control solonoid was also sticking. Couple drops of air tool oil in the ports fixed it up.

 

[dyeager535]

"As you get cash" should definitely include buying a GM service manual for the truck.

Guaranteed they will have testing procedures for just about anything you have problems with, and flowcharts to make it all make sense.

 

[Mav2u]

Yep, I got the Helms manuals but they don't address anything about this in there. Especially if it's a ignition problem or a transmission problem.

Its nice to troubleshoot if you can have a starting point to begin. If someone else had the same problem as I describe then I can start their and work off their suggestions and how they came to figure out the problem.

If it's not the problem then its one more thing I can scratch off the list of things to try between working 55 hours a week and going to school part-time. If I had more time I would spend all day taking the old beast apart but since it is my only vehicle I can't risk breaking something right now when I'm trying to troubleshoot it.

Vacuum leak is not going on since I only have like three lines and all of them have about 20 psi of vacuum, yeah I already checked that and the functioning of the EGR solenoid. Only problem is there is no way of actually checking the EGR valve since it is one that cannot be vacuum gauge tested.

So any other suggestions are welcomed as this problem is giving me a headache.

 

[Thunder]

The pick up coil is the round thing on the Dist shaft. Yes they do go bad. You have to pull the dist to change it. Put an ohm meeter between the white and green wires that come off of it. Use the specs i posted eariler to check it out.

 

[dyeager535]

I know for a fact that one of the issues addressed in the Camaro Service Manual is a "surge or chuggle in gear".

It's under driveability and emissions IIRC, I would be VERY surprised if the Blazer Service Manual didn't have similar.

 

[daleearnhardt01]

My Helm Blazer manual for 1990 has a separate book for driveability, fuel, and emissions....Ill take a peak for you when I get home tonight...

 

[Mav2u]

Yeah, I gots the same book lurking around here somewhere. I'll take a look in that thing also.

Appreciate the help on this, now to take out the distributor, which I've never done before.

Any tips on taking it out and installing it again. Any make sure you do this and don't do this things to mention before I do this.


Thanks,
Mav