Engine misfire? And a couple other odd issues

[miamibob]

If you're not sure, replace the cap and rotor. Cheap enough...

[sly]

the burned marks... scrape them clean. See if that helps.

It may also be time to run a tank of fuel injector cleaner. I may need to do that to my 88 as well cause all my misfire is at low RPM (so I know it's not a fuel delivery issue - though the filter may need replacing as well since I haven't touched that in at least 2-3 years).

[L1011tristar17]

I just threw on a new cap, rotor, air charge temp sensor, and ignition coil. It made a slight improvement but the misfire is still there

[miamibob]

Non OEM sensors could be an issue. Temp sensor, maybe??

[L1011tristar17]

Are you talking about the one I replaced? The old one was looking crusty. I have another OEM one from a junkyard car that looks decent so I might try throwing that on there. The coolant temp sensor is pretty new. I had it replaced when the lower intake gaskets were done.

[sly]

I've had no issues with the AutoZone sensors on the whole. Rarely I get a bad one, but they're completely bad, so easy to find out. None of that half assed stuff. Now getting the old harnesses to make good contact can sometimes be the issue. Also, make sure the harness on the TFI module is good and secure. I had an issue where the connector would slide loose on mine because the clip was loose. Ended up waiting for a hot day (engine hot too) and put some dielectric grease on the gasket inside the harness and some more on the pins and shoved it back together to create a sort of a vacuum seal as the air inside will cool and contract and keep the harness on a little better. This only works for a while though, but it was enough to allow the clip to bend back to it's original position and keep things in place. Failing that, a long zip tie will also work.

[miamibob]

I was referring to the sensor that sits on the driver's side near the first or second plug from the radiator (looking form the front to the firewall).

[L1011tristar17]

There are two coolant temp sensors. One goes to the computer and the other to the gauge. The one to the gauge is pretty new (replaced last year) and the other one was in decent shape. I had it out while I was swapping intakes so I got to see what condition it was in.

Parts replaced so far:
Cap and rotor
Plugs and plug wires
Ignition Coil
TPS
Air Charge Temp Sensor
Fuel Filter
Reset timing

Where else should I be looking? MAP sensor? Fuel Pressure Regulator? And what is the likelihood of it being something internal in the engine, such as a bent valve or stuck ring? I have taken good care of the engine and checked and changed the oil often, so I'm hoping that isn't the issue.

[miamibob]

MAP sensor - especially the vac line/s to it. I think the sensor going bad is a long shot. Vac line is more likely, IF that area is a problem.

[L1011tristar17]

Misfire seems to be at the point where it was before I started throwing parts at it. Car stumbles on initial acceleration and surges a bit when braking. The misfire is enough to shake the entire car at a stop and it's now continuous (as opposed to earlier where it would misfire every 2-3 seconds). When looking under the hood I can see the motor shake while idling. I feel like I'm driving my sister's 4cyl Dodge Stratus lol.

I am wondering if at this point it could be vacuum-related. Most the vacuum lines are fairly new from the last time I had the upper manifold off. I was thinking of doing a cheap smoke test (a cigar) to see where a leak might be. That might also solve my issue with the cruise control.

Sly, I checked the TFI module and it's on pretty tight. Good suggestion though. I know those parts are usually the weak link in anything ignition related. I already had to replace it once.

[gadget73]

have you checked this for codes recently? Sometimes it actually outputs useful stuff. Not always though. The check engine light almost never comes on, so pay no mind to the fact that its not lit up.

[L1011tristar17]

I think I can hear a bit of a vacuum leak coming from the back of the engine while it is running. MAP sensor vacuum line is one of the few I haven't replaced yet and I don't think it is long enough anyways. What size line do I need to get?

[L1011tristar17]

I just pulled some codes:

34 (as expected)
74 (didn't press the brake)
94

When doing the KOER test, the scanner thought my car was a 6 cylinder. Thoughts? I also did a cylinder balance test and got a code 90 (all cylinders fine)

I also got some video of the misfiring, which I will upload. It seems to go away at higher RPMs

[L1011tristar17]

At least with the cylinder balance test, it doesn't seem like there is anything wrong with one specific cylinder (i.e. burnt valve, bad injector, bad plug). The next things I will check is fuel pressure and for any vacuum leaks. If none of those work, I have no clue what could be next.

I read up a bit on the code 94 I got. It seems to be for the air injection on the driver's side. I heard that it is possible for a faulty O2 sensor to throw off the air injection sensor on that side. Do you think that could be the case?

EDIT: I also popped off and capped the vac line to the EGR while the car was running and it didn't make a difference. I guess I can rule that one out too.

[sly]

you have to also pull a vacuum on the egr valve when you do that and see if the car stumbles badly or dies like it should. Then the EGR valve is good. If no change when pulling a good vacuum on the valve, the valve is either bad or the passages are clogged.

laggy O2s will cause all kinds of stupidity. I generally change those every 100K-150K or so if they don't bring up issues before then just for good measure.