Need help - running rough

[jtmarten]

My '96 K2500 w/7.4 is running rough. I've replaced:
cap, rotor, fuel pressure reg, injectors (Bosch Design 2's), plugs, wires.
Had it timed today and it still runs rough. Really rough sometimes. I'm getting no codes.
In the morning when the engine is cool, I'm going to pull the pugs and check them, and verify the plug wires are installed correctly.

Any other thing(s) to check??

I'm supposed to leave for the Chicago area with it on Tues, but not if its running this poorly.

[j cAT]

Originally Posted by jtmarten

My '96 K2500 w/7.4 is running rough. I've replaced:
cap, rotor, fuel pressure reg, injectors (Bosch Design 2's), plugs, wires.
Had it timed today and it still runs rough. Really rough sometimes. I'm getting no codes.
In the morning when the engine is cool, I'm going to pull the pugs and check them, and verify the plug wires are installed correctly.

Any other thing(s) to check??

I'm supposed to leave for the Chicago area with it on Tues, but not if its running this poorly.

with no codes fuel pressures must be read and the test proceedure done. no leak down on pressure. pressure to 60-65psi and hold key on engine off.

if you run on 1/4 tank all the time the fuel pump is most likely cooked especially with all the 90 plus heat.

if you have bad wires/rotor/cap/distributor/maf/map etc you will get codes !

[jtmarten]

The dealer checked the fuel pressure, dist gear, etc.
I always try to keep at least 1/2 tank in it, very rarely let it get below 3/8 tank. It very rarely gets used, maybe 2-3k miles a year.
Today I'm going to make sure all the plug wires are correct, if so, I'll prob replace the coil and the ICM.


Checked wires, all OK. Pulled the coil assy and will replace the coil and ICM.

[j cAT]

Originally Posted by jtmarten

The dealer checked the fuel pressure, dist gear, etc.
I always try to keep at least 1/2 tank in it, very rarely let it get below 3/8 tank. It very rarely gets used, maybe 2-3k miles a year.
Today I'm going to make sure all the plug wires are correct, if so, I'll prob replace the coil and the ICM.


Checked wires, all OK. Pulled the coil assy and will replace the coil and ICM.

why did you bring to the dealership ? you only go there to buy a vehicle or have warrantee work done.

why would they fix an old vehicle like yours. your the reason they are not making a lot of money.anything over 8years old the dealership will not fix it and I doubt they have parts in stock to do so !

since it appears you lack skills and the equipment to do all this bring to a repair shop that has a good reputation and is honest. post back what they did .

fuel pressure must be tested. 60-65psi ..........

[jtmarten]

New coil and ICM installed, and she's running much better. Still has a bit of a miss in the low end, but otherwise runs nice and smooth.

I took it to the dealer to get it diagnosed since there are so many things that can cause a miss. Wanted to eliminate a few things. The dealer is about the same $ as an indie shop here. They checked the fuel pressure, but of course they list no numbers on my invoice, just shows its OK.

Their technicians also don't have the skillset to work on them. The loser that worked on mine lost one of the dist cap screws, tried to use a tiny philips-head screw that was too short to bite anything, so my cap was flopping around on the dizzy. AND, the idiot left my driver's window wide open in a major downpour. Had a nice long chat with the dealership manager about it.
Guess I'll have to break down and buy a fuel pressure gauge later today just to eliminate the pump.
Why do you assume I have no skills? Lately (last 3 weeks or so) I've replaced the coil pickups on my Intruder 1400 (NOT an easy feat but it beats $600 for a stator/pickups assy); replaced the radiator, hoses, belts, tensioners, pulleys, etc on my BMW V12 850Ci; replaced the main belt, tensioner and pulley on my Aurora (PIA, but not as bad as the belts were on my old Bonneville SSEi); and replaced cap, rotor, wires, plugs, injectors, FPR, coil and ICM on the 'burb.
In a few weeks I'll be pulling the C4 out of my '64 Falcon 'vert to replace the bell housing and TC, then a few weekends later upgrading the BMW from a 2.81 open diff to a 3.15 LS.

[jtmarten]

Fuel pressure is
56psi with key-on
After turning the key off I watched it for several minutes and saw only a negligible drop in holding pressure: about a 2psi drop
58psi while running

[j cAT]

Originally Posted by jtmarten

Fuel pressure is
56psi with key-on
After turning the key off I watched it for several minutes and saw only a negligible drop in holding pressure: about a 2psi drop
58psi while running

pressure is good for my 2000 silverado . Not for a 1996. 60-65 key on eng off.

recheck my opinion on your correct fuel pressure.just to be sure. could be a voltage drop to the fuel pump/or relay voltage drop. drive around with gauge hooked up see if it wanders lower.measure voltage at the pump make sure the frame rail ground is secure.

56 psi is too low.

the reason I believed you did not have the tools / ability was because you brought an old vehicle like this to the dealership.

also working this yourself you know it was done correctly with the proper tools and manuals.

do you really think those techs at the dealership have a clue what the specs are on this old 1996 ? I know they do not stock parts for it that is why they half azzed your dist cap.

I worked at the dealership its all bad !

[jtmarten]

Would the new FPR have anything to do with it? The spec for it shows a working pressure of 50.

[j cAT]

Originally Posted by jtmarten

Would the new FPR have anything to do with it? The spec for it shows a working pressure of 50.

fpr =fuel pressure regulator ? that spec should be 62psi.

I did a little checking . ya fuel pressure in the 50's is a no go deal.

I now believe its eng off key on 62-66psi.. when the engine is running the pressure guage will drop a few psi. most likely in the upper 57psi area with pusations as the injectors are open/closing so the needle will flutter. when you rev engine the pressure should not drop if the pump/filter is good.

pinching the return line the pressure should spike upward to 70-80psi . when the ignition is turned on the pressure should shoot up fast. pumps sometimes die slowly as they loose torque.

recheck your part supplier and make sure you have the correct parts.

recheck the spec for your vehicle. I dont have the 1996 OEM manual.