Cylinder 2 Misfire - Can't track down the cause

HoeLV

Newbie
Joined
Nov 17, 2021
Messages
3
Reaction score
1
Location
Las Vegas
I am hoping you guys can help me find the gremlin that is haunting my #2 cylinder.

The vehicle: 98 Tahoe, 2 Door, 4WD, 5.7, 223K miles - no knowledge of maintenance prior to 176k miles prior to purchasing the truck myself.

I will try to quickly run down everything I have done already trying to fix the issue as well as recent history of work.

Little backstory and recent work:
Originally, I was having some random misfires, especially under load, rough idle, a random O2 code here and there. I wasn't quite sure if I was looking at a fuel or ignition issue, but it was also time to do some tune-up type things regardless and I hoped the random misfires and such would be resolved when done.
About 3 weeks ago (222,500 miles) I went ahead and replaced the spark plugs (AC Delco 41-993), plug wires (AC Delco 9718Q), distributor rotor (AC Delco D465), distributor cap (AC Delco D329A) and did the CFI to MPFI (Standard Motor Products FJ504 injectors w/ gaskets and bracket) swap including a new fuel filter, air filter and oil change. When all work was done, smooth as butter. Really, the truck ran phenomenally for about 400-450 miles, by far the best since I had bought it.
Then out of nowhere, start getting a bad misfire. I pull the codes and P0302, cylinder 2 comes up. None of the cylinders throw misfire codes, no generic code for misfires. Just cylinder 2. So I started trying to determine the cause.
First, ran compression test - checked each cylinder twice. This seems to look fine.

Cylinder 1 - 165 | 165
Cylinder 2 - 169 | 170
Cylinder 3 - 167 | 170
Cylinder 4 - 170 | 168
Cylinder 5 - 170 | 167
Cylinder 6 - 160 | 165
Cylinder 7 - 164 | 172
Cylinder 8 - 173 | 170

Next, fuel pressure test. Numbers appear to be a little low, but wouldn't that affect other cylinders as well? Not just cylinder 2?

Key On - 60
Idle - 52
10 Min - 52
Driving/Missing - 55

I also swapped the plug and plug wire from cylinder 2 with a different one to see if the issue would follow the plug or the wire. Neither swap made a difference.

At this point, I noticed the plastic screw tab on the distributor was broken and the cap wasn't seating 100%. Great, I go ahead and replace the distributor as the original one was still in use. Based on recommendations, I put in the UNITED MOTOR PRODUCTS 9362 distributor and UNITED MOTOR PRODUCTS DCR820X cap. I verified the CMP retard is within spec at -1.4 degrees.

Still running rough and getting P0302 almost immediately if I clear the code.

Any thoughts or ideas? Things to look at next?

Thanks for any help.
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
2,810
Reaction score
3,297
Location
Dallas, TX
60 psi with key on, engine off is within spec. I think you can rule out fuel delivery issues (fuel pump.)

A fuel delivery problem would cause multiple misfires on both banks AND a lean code.

Since your idle pressure seems a a bit low (I don't remember the actual spec) it could be fuel pressure regulator.
 

Latest posts

Forum statistics

Threads
56,051
Messages
1,232,320
Members
39,844
Latest member
Brianwd83
Top