Interesting stuttering problem I've been having 1985 Z51 with a Tremec TKX 5 speed. Lately the car seems to stutter at random when accelerating. It frequently happens when the car is under load, like pulling up a hill, driving at night with all the lights and accessories going, and frequently just after going around a corner from a stop. The latter made me think maybe the fuel was sloshing in the tank, but I filled the tank and it persists. Whenever it happens I just push the clutch in, wait a second and then let back out and go on my merry way.

My entire fuel and ignition system has been replaced since I bought the car a year and a half ago, but it suddenly started doing this in January. As mentioned, it seems to happen more at night and frequently after just completing a turn from a stop. It has happened in a straight line getting onto the freeway in the daytime though.

I've got a mind to check the plug wires as I had difficulty getting them off in December to check my plugs and wound up pulling the end off of one of them. I replaced that one wire but the other 7 are about a year and some change old. Additionally my power steering pump is leaking and seems to be on the way out, but my power steering still works, it just groans sometimes and makes me wonder if that's putting too much load on the engine.

Thoughts? Anyone dealt with a stuttering issue like this one? I searched the forum and found issues similar to this one but not quite the same.

 

Yes, i had the same on my 85 years ago but i didn't associate it with any turn, stop, etc. I would check fuel pressure by taping a fuel pressure gauge to the windshield and observe while driving.

My pressure was low due to ruptured fuel pulsator (in tank), leaking injectors, old fuel filter. I added an adjustable pressure regulator, bypassed the pulsator with a piece of fuel hose, changed the injectors/filter.

All of this cured my smoky hard starts, stumbles, etc. I also had a fouled plug way back when that caused a misfire. - but sounds like you checked plugs. Lots of good write ups on fuel pressure testing on the forum. good luck.

 

I'll definitely be driving around with the fuel pressure gauge on the windshield to test. It's just odd because everything from the pump to the injectors is new. I also eliminated the pulsator while I was doing this. I drove it for about a month without issue after changing the fuel pump before it started doing this, but maybe something's come undone somewhere.

Also my plugs aren't fouled (last I checked) but they do have some oil buildup from leaky valve guides

 

Something I feel I should also mention is my car does have a slight intake gasket leak. There's a little bit of coolant at the front left corner. It's been like that for a while now and so far hasn't seemed to cause any drivability concerns. I've recently heard this can oil the plugs up a bit. Not sure if that might be part of the problem.

 

It is a "wet" intake - so if like mine, you might be burning a bit of coolant and not even noticing. I could see that on my plugs but not as oil.. white residue. tolerances are tight where the coolant passages route into the intake.
You should probably gear up for an intake manifold gasket change. That is a great time to replace the injectors if you have leaking ones.

 

When I had the plugs out in December they didn't have any white residue but bits of oil caked on in spots. Unless the leak has gotten worse since then. The injectors are new as of 2 years ago.

I've been dragging my feet about that intake manifold gasket 😬

 

Wet down the ignition wires and watch for spark to jump.

 

Update: just tested fuel pressure while driving. It held at ~40psi the whole time, even during the stutter

I'll be testing the plug wires next. There's a chance I might have yanked one of the ends loose when I took them off in December. I broke the head off of #6 back then and already replaced it. It's odd that it only does this in high load situations, but then again my old distributor cap was completely bad and it only acted up at high rpm

Is there anything in the drive line that can cause something like this? I haven't replaced my U joints yet and my batwing bushings are original.

 

When checking spark plug wires, I use a test light connected to ground and drag its probe along wires and boots. Seems to make it easier to find where the problem may be. 🤓

 

I assume the test light lights up instead of zapping you?

 

Update: did the water spray test

Every single spark plug is flickering on the outside

What on earth is that? Did I not tighten them enough when I put them back in? Did my old plug wrench beat them all up? I've got spare plugs but geez

Also one of the plug wires has a faint spark where it touches the hood release cable.

I'll be swapping all that out tomorrow but this beats all I've ever seen. I had noticed that the plugs had a sort of white chalky buildup on the porcelain recently. And the plugs were new on 2024. What in the world...

 

Looking at the FSM I notice mention of corona discharge, which is described as "a steady blue light appearing around the insulator, just above the shell crimp." Apparently this is normal and only visible in darkness. So there's a chance the only spark leak I have is at the one shorting to the hood release cable.

 

I replaced the plug wire that was arcing to the hood release cable. It seems it had been rubbing on the edge of the distributor cover. It's now routed away from that, but the problem persists. Still stutters occasionally under heavy acceleration. From what I can tell there's a persistent carona discharge around all plugs, but two of them seem to have faint flickers at the exhaust manifold further up the spark plug boot. Annoying since I just replaced all of these a year and a half ago, but oh well. I'll swap them and see how it goes.

 

To be honest, I don’t recall looking at the bulb. The test light handle is insulated and the probe supplies a ground path for spark from leaking wires and boots.

 

I might have to try that. The water spray method was pretty effective but there's one spark that I only saw out of the corner of my eye once or twice that seemed to be jumping to a screw on the firewall

 

While I'm in here does this chalky buildup on my plugs seem strange to anyone?


I should also probably mention that they looked like this when I pulled them out in December


(#5 is really clean because the PO swapped the CSI plug with the #5 injector plug, so it was getting washed on startup and then not getting any fuel while the engine was running)

I've been told the rest of the plugs look like that because of leaky valve guide seals

 

Did you use a lot of the wrong type of anti-seize on the plugs? Dan

 

I used the dialectric grease they sell at the counter in the parts store that says it's for plug boots. I've never used it before on anything else but these plug wires were on there tight so I thought I'd make it easier on myself. I saw one person say dialectic grease has given them problems before but I'm not sure how that could be. No anti seize on threads themselves.

 

I use a very small amount of anti-seize on the plug threads. I use the kind made for plugs that DOES conduct electricity so the plug can ground. Dielectric grease does not conduct electricity and should be kept off the plug tip and the wire metal connector. Dan

 

That's very interesting to know. I'll have to clean all that stuff off the plugs and wires later.