Rough Idle, Misfiring and bucking...

[onefstsnake]

Well I just got the 93 running not to long ago.

Its been idling quite rough. (sounds like it has a giant cam in it)
But once I give it some gas it smooths out.
While driving it vibrates and bucks when under 3k rpm. And at low RPM and 50% throttle it shakes terribly.
Also at high RPM both the stock tach and AutoMeter tach go crazy and read random RPM's...

Ive changed the plugs, coil, cap and rotor and it hasnt had made any noticable change...

All the vacuum lines are where they should be, every connector is connected correctly. I know its running on all 8 cylinders.

TFI Module take a dump?

BTW Timing is at 10* with SPOUT out and FP is at 35psi at idle w/ vacuum line connected.

 

[U2SLO450]

did you look at the computer, i had mine burn up one time and it did the same thing

 

[onefstsnake]

If the A9L burned up the car shouldnt run...

 

[91lxttrim]

Or the computer ground near the washer fluid where the battery goes. If that is loose or corroded it will act like that

 

[v8only]

the VERY first thing you need to do is pull codes, that alone may tell you what's going on.

check everything else, including your tps...

 

[Fuzion]

Was the coil not the problem?

 

[onefstsnake]

I replaced the coil with the one that I had on the car before going to the MSD coil.

No change. All grounds are good.
Ill check the codes in the morning.

 

[4G-KDMP]

I replaced the coil with the one that I had on the car before going to the MSD coil.

No change. All grounds are good.
Ill check the codes in the morning.

from everything i've read before thats the 1st thing you should do, seems to be the cheapest way to go instead of just throwing part at probelm that you can find or track down.

 

[onefstsnake]

yeah. Well everything that ive replaced so far needed to be replaced.
The cap/rotor were pretty burned up, plugs were fouled from a previous rich condition, and the msd coil was broken.

 

[onefstsnake]

Well The car is throwing codes 41 and 91 during the KOER test.

So its saying both banks are lean. But I just replaced both O2 sensors a few days ago...

What gives?

 

[v8only]

is your smog pump bypass working? perhaps it's still dumping fresh air into the heads and past the o2's, causing a lean condition.

 

[HISSIN50]

I know you've been over and over it but it still sounds like a vac leak. This will cause a rough idle and can cause lean codes (the chances of two new O2's being bad are about nill, so I look at issues that can cause systemic problems).

A stockish motor should pull about 20" hg of vac at idle.

If it continues to idle real rough, I might consider a cylinder balance test to see if it can pick up one particular cylinder that's causing an issue. The thing with one goofy cylinder is that once you get the RPM's up, the sheer number of revolutions per minute mask the defect.

Good luck bud.

 

[onefstsnake]

The O/R H pipe im using has no provisions for the smog tube, so the tube is capped off.

I dont see how one of my cyliders is dead, or down on power. The car ran fine prior to the intake swap.

Ill check vacuum, then try some propane. And maybe a compression test.


Im also having a problem with the gas tank, everytime I take off the gas cap there is a considerable amount of pressure release from the tank.
Ive checked the purge solenoid and there is lots of vacuum going to the solenoid... But this probably isnt related to the idle problem

 

[v8only]

i'm not talking about the smog tube to the h pipe, I'm talking about the bypass tubing that goes to the back of the heads...during cold startup, the smog pump directs air to the back of the heads which come through the heads and out the headers, and in turn past the o2's...this leans out the o2's which fools the computer into a run rich condition for startup....this is why I mentioned it, if it's stuck going through the heads, a lean o2 condition is "possible"

 

[HISSIN50]

With the EVAP issue, the purge solenoid might not be opening. If this just came about as temps got hot, it's not super uncommon.

Jeremy was talkin about the plumbing that goes from the smog pump to the back of the heads. If a solenoid was stuck (we'd hope it would toss a code but who knows), you'd have lots of O2 being introduced into the exhaust, upstream of the O2's. That was an interesting idea by Jeremy - I hadn't thought of it before.

You don't have an aftermarket ignition box, do ya?

 

[onefstsnake]

well all the piping behind the heads is good. and the bypass works fine I guess.

The Purge Solenoid hasnt been working since I bought the car. Either that or my canister is plugged up/full.

I run an MSD 6AL for ignition. Its ~1 year old and is mounted inside the car. Its still buzzes like it did when I bought it. Doubt that its the problem.

 

[onefstsnake]

Well I pulled all the wires today to see if I could see any arc spots on them... Nothing...

But when I put them back on this evening I noticed they are arcing around where the spark plug is... I made sure they were on tight, and they were. So Im guessing the wires are bad?

I ohm'd them today and they were reading anywhere from 1.3K Ohms (short wires) to 2.8K Ohms (long wires).

 

[4G-KDMP]

bad wires will do it everytime but i'd still supect the MSD 6AL for ignition.

 

[onefstsnake]

well I even disconnected the 6AL and ran the coil off the stock ignition. No change.

Ill Probably pick up a set of Accel wires tomorrow at work. 30% off retail! lol

 

[HISSIN50]

I'd see about getting some boot insulators as well.

Good luck.