About 6 months ago I had C E light come on. Did the key trick and code 43 came on. I replaced the cap and rotor and plug wires and routed them as per TSB. Plugs are only 2 years old and they looked fine, so I left them alone. That fixed the problem. Yesterday, driving along and I decided to mash the gas pedal for a brief full throttle run, and at about 3200 rpm it stumbled pretty bad and had a tough climb climbing to 4000rpm. CEL came on. I backed off the throttle and the engine ran fine. About 20 miles later I floored it again and same problem. The key trick shows code 43. The engine runs excellent unless you try to climb over 3300 rpm under load. And for a couple years now at a warm idle and in gear (ex. Traffic light), it idles very slow and stumbles occasionally. Not sure if these problems are related, or not. Suggestions for this latest CEL?

 

Code 43 is for the coil. Check primary and secondary resistance, and see what things look like.

 

Code 43 is a misfire code(or coil) according to the 96 service manual. There are more P0# codes under it for a better description of the problem. See if can get the P0# codes read it will give you a better description if it's the coil or a misfire. How is your plenum?

 

This is what the '96 manual says: DTC 43—MISFIRE MONITOR
Excessive engine misfire results in increased catalyst
temperature and causes an increase in HC emissions.
Severe misfires could cause catalyst damage.
To prevent catalytic convertor damage, the PCM
monitors engine misfire.
The Powertrain Control Module (PCM) monitors
for misfire during most engine operating conditions
(positive torque) by looking at changes in the crankshaft
speed. I f a misfire occurs the speed of the
crankshaft will vary more than normal.


If you can get it scanned for the "P" codes, P0301-P0310 are for cylinder misfires and P0351 is for the coil.

 

Ok, so I used a code reader and got the following codes:
P0300
P0303
P0304
P0306

I have reset the CEL 4 times in the last couple days and the light stays off, unless I do a wide-open throttle run. Normal driving doesn't trigger the light, or the symptoms. I have to try to make the light come on by hitting 3500 rpm.

Spark plug wires caused very similar symptoms 6 months ago, and replacing them and re-routing them fixed the issue. Could these wires be NFG already? They are Champions, FYI.

I removed the air cleaner assembly and opened the throttle-body and peered down there with a flashlight, as I have done annually for over 10 years (I'm the original owner). There is oil residue down there (Just like 10+ years ago), but definitely no "pooling" to speak of. No significant changes to report there. Any other way to determine if its a plenum issue?

I also replaced the cap and rotor about 6 months ago, but the distributor itself is OEM. Could that be my issue?

Any other thoughts?

 

Pull the PCV, tape over the hole in the valve cover, and plug the vacuum port on the manifold.

Do the same for the vent hose on the other side. (or, just pull the hose, and plug it.)

Take off the oil fill cap.

Start engine. Just let it idle. Put your hand over the oil fill hole. Do you feel a breeze? Or does it try and suck you in? You should feel a breeze. If you don't, plenum is blown.

How is your fuel pressure at speed? (very little demand at idle, so, pressure may be fine there, but, when you are leaning into it, pressure may be falling off, so, you end up with a lean miss.)

I have also seen similar symptoms with a failing crank sensor. (and no, it won't necessarily set a code..... mine didn't.....)

 

I've been working out of town and finally had a look at the truck today. Since the codes were indicating misfires on cylinders 3,4, and 6 so I decided to replace those plug wires. In December (8 months ago), at night time I could visually see the coil wire arcing (truck wouldn't start), so I bought a set of wires and replaced all 8 plug wires as well as the coil wire. I kept the 8 plug wires in my garage. Anyway, today I replaced the wires for cylinders 3,4, and 6 with those used wires I had in the garage. I also removed the spark plugs for those cylinders and the plugs looked great. Possibly lean looking, as there was no darkness to them at all but overall pretty satisfying. Then I did what "Hey You" suggested and plugged the breather holes and started the engine. I didn't feel much of anything at the oil cap hole, but when I plugged the oil filler hole with the palm of my hand, I could see the duct tape I had placed over the valve cover holes tighten up and pressurize. Then when I'd remove my palm I couldn't definitely hear pressure escaping from the oil filler hole. I figured my plenum gasket is good. What a relief. Then I used my brand new Autel A519 to reset the codes and then I went for a drive. I did 7 full throttle acceleration runs from 0-100mph and the engine didn't misfire at all. It ran perfect, and didn't set any codes. I'll keep an eye on things, but I gotta say I have replaced plug wires in that truck probably 3 times over the last 4 years. Happy for now...