Hey guys. I have been struggling with this for a little while, and Im hoping you might be able to help me out. Here is a breakdown of the issue:


What I'm working with:
1994 4x4 2500, 5.9 gasser (newer/low miles) with a standard trans behind it.


The problem:
Under load, (moderate to heavy acceleration or towing) The truck stumbles as if starving of fuel or spark. Idles great, light acceleration is smooth. Not throwing any fuel or spark related codes.


Things Ive already done:
New cap, rotor, wires and plugs. Reset fuel timing/sync via distributor. (Had it at "0," advanced it to +3 ish.) Fuel pressure is between 39 and 42 PSI throughout the RPM range. (Measured at supply line just before fuel rail).


Other things to consider:
I have no catalytic converter. Compression is around 155psi across all cylinders. Only code thrown is for EGR solenoid switch, which has been on since I rebuilt the engine over a year ago.


Any help would be great guys, thanks!

 

How is your spark at the plugs? How old is the crank sensor? Has the plenum been fixed?

 

Crank sensor is fairly new. I put a new one on it about a year ago.


Plenum is fixed with the thicker aluminum plenum plate. I did however inspect it anyway, and I see no signs of gasket failure.


I haven't measured spark at the plugs. The only method I have to do that, is by visual inspection. I do not have an inductive meter. Just a multimeter.

 

Visual inspection will be fine. You are checking for good, consistent, spark, at all cylinders. (you can just test off the coil wire for that matter.) gdstock discovered that not all crank sensors are created equal, and one that didn't always trigger properly would result in consistent weak spark on one or more cylinders. That was enlightening.

 

Hmmmm... The crank sensor idea is interesting.


I will inspect my spark situation before I go into work today.


Any chance my coil is dying? It is older, off of a donor truck.

 

Typically the coils are neve. A problem on these brutes. However there is a new coil laying in my passenger seat.

That I have not installed due to stripped screws that they hold them to the engine with.......

 

I had the same problem when I took this coil off for the rebuild. I had to use a dremel and a cut off wheel to cut slots in the screw heads, so I could use a giant flat head screwdriver. That worked well. They must have used some mild steel in those screws, because it seems to be a fairly common problem. I try to use the appropriate sized screwdriver when I can, and it stripped them out anyway.

 

I pulled a wire off of one of the spark plugs and plugged in an old spark plug. Huge spark. Small bolts of lightning kind of spark. I revved the engine while doing this, and it didn't seem to fluctuate in strength. Should I be looking at fuel injectors? Could I have one or two that are going/gone bad? Any other suggestions?

 

Power balance test.

Start engine. Let it warm to operating temp. Shut it off.
Disconnect IAC motor.
Start engine.
Unplug fuel injectors one at a time, and record RPM drop.
Do all eight.

See what your numbers look like. They should all be within 10% of each other. If they are not, the cylinders with the LEAST RPM drop, are your problem children.