AgentEran

My LT4 has been sooo good to me.. very consistent performance. So when i added a qt of oil before a drive it first took forever to start.. was just turning and turning.. when it did start a small amount of smoke came out from under the hood. The car is obviously missing on a cylinder and the idle was high (2k).. i drove it a bit and i can really tell there is some hp missing and when i would come to a stop the idle is high, between 1 & 2k rpms.

So diagnosis you should ask yourself whats different that could be causing the issue and the only thing different is that i added oil, it literally ran perfect up to this event.

What could this be??

ive ordered some valve cover gaskets from rock just now and i plan on taking a look at the valvetrain.. maybe check spark plugs for oil fouling??

AgentEran

Ive run both my scanners and there are no codes.. i tried entering mode $6 but the scanner says "vehicle does not support mode $6".. Is this accurate? All 96s cant enter this mode? I tried on the other car and same error.

ls777z

Did you accidentally put in blinker fluid instead of motoroil?

​​​​​​​I would start looking around the manifold for disconnected wires or vacumn lines. There's a chance you might have knocked something loose.

bac22

A quart of oil?!? Either you have a pretty bad oil leak or you're burning oil. You didn't actually overfill it with oil, that will cause serious problems, although not sure that would explain your current problem.

So far common culprit is adding a quart of oil, pull out a quart and see what happens.

dizwiz24

Maybe a spark plug isn't firing. Have you replaced spark plugs / wires recently?
Check the vent on the optispark also, make sure its still working. IM hoping you have an OEM optispark (vs. an aftermarket replacement).

Paul Workman

I doubt adding a quart of oil is the culprit. High idle almost always is indicative of a vacuum (air) leak - e.g., a hose that fell off or manifold gasket - and neither will toss a code. (Timing too has been known to alter idle - just something to keep in mind.)

96+ GMs are OBD-II motors. However, a vacuum leak wouldn't show up as a code, FYI. (Been there...Done that!)

AgentEran

lol that would be a rookie mistake!

I did this this morning.. nothing is loose, besides that you dont have to bother anything to get to the oil cap so this prob isnt whats happening.

AgentEran

Indeed, I have both.. it leaves a couple drops of oil every time I drive it and its burning a little oil too. Over the last few years I loose a qt of oil every 30 days or so. I let the oil go as low as the "safe line" on the dip stick, then I add aout a qt to fill it to the top of the "safe line" on the dipstick.

AgentEran

Nope, these plugs were put in new about 3 years ago when I put the long tubes on.

last time I dealt with the opti was when I did the water pump back in June. everything was good, made sure vacuum lines were good and cleaned it up . This is a replacement optispark that has the Mitsubishi optical sensor, this was done by the previous owner ~ 2009 IIRC. I have the receipts in the folder that came with the car, i can double check.

AgentEran

Thanks I appreciate all the replies and help. Im with you here, as far as the addition of oil alone would not cause the issue. What I dread is the possibility that some foreign material got into my valve train when I put the oil in.

AgentEran

So now I'm at work and I'm worthless because all I can think about is that car.. When the car is running great, I feel great. When the car is running bad, im no good. In fact I usually drop everything I am doing, everything, and work on the car until I either fix it or know with a fair amount of certainty what the problem is.

I have the valve cover gaskets on the way, should get them tomorrow. So when I leave work today I plan on pulling the plugs, checking them, use a noid light. Look into the cylinder through the plug holes using a endoscope.. and inspect the upper head/valve train.

The one PIA I already know im going to have is getting the plugs out cylinders 1 & 2 because the headers are directly in the way, and it looks like I may have to unbolt them to get to those plugs

Anyone think im knee jerking on my approach here?

turbobuick33

How many miles on the LT4?

AgentEran

140k

AgentEran

I managed to remove and check all 8 spark plugs.. they all looked uniform and normal. None were fouled or oily or black or anything like that. This was the closest thing to an issue I could find last night.. But im not sure this was the issue:



When I ran the engine with that particular wire off, it did run the same.. with the same miss, it didn't degrade further, nor did it throw a code..no code with an entire cylinder off???

AgentEran

As an update.. I ordered some new plug wires and they finally came.. replaced the plug wire that was burned and ol Blackie is back! Went for a 1.5 hour drive and didn't miss at all. VERY satisfied with this. Vette gods had pity on me!

1993C4LT1

Since it ran the same with the plug wire off, that would indicate the wire was the cause.

AgentEran

Indeed!

I'm as happy as a runaway slave!

turbobuick33

AgentEran

Taylor Thunderbolt 8.2mm.. they are pretty good quality and made is the US!

I did not replace the plugs themselves bc I wanted to make sure I found the issue first before upgrading or changing anything.

turbobuick33

Whats the part#? Are the wires red? Do they fit well in the stock wire looms?