Lots of symptoms, help me diagnose!

[B94Sport]

This one has been bugging me, maybe someone else knows what is going on:

First, when I start my truck, it will idle around 1200 RPM for a while, rather than the usual 800 or so RPM. When I drive it, acceleration is very slow up to about 30 MPH. Also, when sitting at a stop light or simply taking my foot off of the brake and letting the truck move forward or reverse, there is a noticable shake from the engine, so much so that the exhaust pipe will shake. The exhaust also sounds different, like a sputtering. The shaking feeling and exhaust sound remind me of sitting in my roommate's 1970 351 Mustang. Above 30 MPH, there is no noticable shake and acceleration is fine. It is only idle-30 MPH that is showing noticable differences. Anyone have any ideas? I haven't had a chance to fully investigate yet, but I don't really know what I should be looking for, either. I did put the truck in park and pop the hood, and the engine is rocking left and right much moreso than normal.

 

[EB Bauer]

First thing I would check is the computer codes. This will at least give you a good starting point depending on if you have some codes or there is nothing. I had the same problem with mine. THe computer codes reported a bad O2 sensor. Not always will this be the case though. In my truck the O2 sensor was fouling due to the fact that my fuel pump was pushing more gas than it was supposed to. 78psi instead of like 40psi. This made every thing run really rich. A good signal is bad gas milage or if you smell gas around the exuast. I would check the codes first though. If you don't have a way of hecking the codes you may want to do some other things like cleaning the MAS sensor and air filter. To me it sounds as if it may be running rich. This may be the reason why you don't notice at high speeds. just cause the intake will be forceing air in. At idle you don't get that push of air so if the fuel pump, injectors, or O2 sensors arn't makeing the proper fuel/air mix you may see things as a odd idle, loss of power, bad gas milage. Let me know if this helps. Just wondering if you have any codes coming up on the computer. Hope this helps.

 

[B94Sport]

Well I have an A/F ratio gauge and according to it, at idle mixture is stoichiometrically perfect... It runs richer when I accelerate, but that's what it's supposed to do. About 12 months (15,000 miles) ago I replaced the Throttle Position Sensor, both O2 Sensors, and my Fuel Pressure Regulator. Didn't replace the fuel pump though...

 

[EB Bauer]

That is very interesting. I don't think you would need to mess wiht the fuel pump if you have replaced the regulartor. When my pump went crazy it totaly foulded up the regulator. What kind of gas do you use? Hopefully someone else will chime in here. I am running out of ideas.

 

[B94Sport]

I use 93 Octane, and have a superchip... Don't know if that means anything or what effect it would have if I got some bad gas... I don't think it would be like this though.

 

[jimmiecakes]

Sounds to me like you're dropping a cylinder at idle. I'd start with checking the plugs and wires...... wouldn't hurt to check compression while the plugs are out, either.

 

[B94Sport]

I will check plugs and wires tomorrow when I get a chance. I have a code scanner... Will it tell me if one of the cylinders is losing compression?

 

[jimmiecakes]

Not for '94, I don't think. IIRC, OBDll didn't apply in the Exploder until '95 and I can't ever recall seeing misfire counters on EEClV.

 

[B94Sport]

Hmmm... Okay. Also, one other thing just came to mind, and I am hoping this does not turn out to be my problem. Saturday night a friend was driving the truck at about 75 MPH with me in the passenger seat when there was a loud 'clang' type noise from the front end. Now, I didn't pay much attention and don't recall the exact sound because I was in the passenger seat, BUT I have heard of spark plug tips breaking off. I am hoping this did not happen, what do you think? If I was running on 5 cylinders instead of 6, wouldn't my RPMs at 75 MPH be a lot higher than normal? Also, I sat outside the truck tonight while it idled and the exhaust is making a definite "puff-puff-puff-puff-puff-poof" sound over and over. The puff being exhaust, the single poof being a much quieter, less forceful sound, almost like a pause in the exhaust. Very disheartening.

 

[espnfreak]

Fuel filter? If your fiter is clogged it could cause some idling problems. Its a cheap fix, and good maintenance idea.

 

[jimmiecakes]

I just went through a fouled plug incident on my '92 (looks like deposits from a leaking injector - I hope ). Idled very rough, cleaned up with rpms.

With a non-contributing cylinder, rpm for a given speed will remain the same as with all cylinders contributing. Depending on what it is that failed and the severity of the failure will result in slightly different symptoms. If yours did indeed chuck the end off a plug, there is always a very good chance that it made it out through the exhaust valve with no damage done.

I wouldn't stew on it until you have a chance to check your basics.......

 

[B94Sport]

Alright. Yeah, I would think that if the tip did come off of a plug, it made it out of the engine because there has not been any noise since then, and I'm not sure but it seems like a plug tip bouncing around in the cylinder would be noticable. Tomorrow I'll pull the plugs, wires, and codes and see what I can find. Thanks for the help guys.

 

[B94Sport]

Grrr I just drove the truck about a mile away to pick up two of my buddies, and there are more noises! Not from the engine this time, sounded like drivetrain. Something is definitely going on under there and I intend to find out what it is! I'll post what I know in about 14 hours.

 

[B94Sport]

:frustrate Well I did two things today:

First, I started the truck and pulled the spark plug wires one at a time to look for changes in the idle, theorizing that when I pulled a wire and nothing changed, there was a problem with the particular plug attached to that wire. After pulled all 6 wires two times each, I have concluded that none of the plugs in the driver's side cylinder bank are functioning. I guess there could be something else wrong that would cause a lack of a result on that side also though... Fuel delivery perhaps?

Second, and this was the fun part, I pulled the codes.
Did it twice and got this:

538: Insufficient RPM change during Dynamic Response Test, or Invalid Cylinder Balance Test - Throttle Position Movement, or Cylinder ID Problems...

This does not sound good to me... My roommate and I are going outside to pull the driver's side plugs right now. If anyone could help me make sense of that code and what it means, I would really appreciate it.

 

[B94Sport]

This is what happens when you don't follow directions TO THE LETTER... I was reading that code again and going through the directions and realized that I never floored the accelerator before the codes were sent, as the instructions specify... Man, I feel stupid. Well I did the test again, floored it this time and got code 111: System pass.

So I am betting that my plugs are fouled up. I will let everybody know.

 

[jimmiecakes]

Doo-doo happens - on cars with a PS pressure switch, the steering wheel needs to be turned and those with electronic overdrive need the OCS cycled.

I used to have a problem remembering the AC.... leaving it turned on would generate a code, as well.

 

[B94Sport]

Pulled all three plugs, and each one of them is in a different condition! Hopefully someone on this board can look at these pics and lend some insight. In order from the cylinder closest to the grille, back to the the cylinder closest to the firewall:

Dead Link Removed
Dead Link Removed
Dead Link Removed

 

[JDraper]

Try some more pix, those are waaaayyy to blurry.

One way to check to see if you are getting spark down to the plugs is to hook an inductive timing light up to each wire and see if it works. If it works, you have spark on that wire. However, this won't tell you if it's a weak spark or not.

There is also the possibility of a bad coil pack. That could reduce or eliminate your spark.

 

[B94Sport]

Hmm... Geocities is being a pain about hosting my pics... Oh well. At any rate, I replaced those plugs and wires and now the rough idle and acceleration problems are completely gone. I am going to ask around and see what people say about the condition of the plugs and what could be causing it.

 

[jimmiecakes]

Ray,

e-mail the pics to mechanic@agt.net - I got DSL so don't worry for size as long as they're clear.