OMG: Major car misfiring

[magyar]

1995 Olds Aurora.

My car is going haywire! Ever since last thursday, it's misfiring like crazy with frequent backfiring. It idles somewhat ok, but as soon as I put it in drive, it feels horrible!

It's lost about 80% of its power and as a hard time getting up hills.

I've changed all the plugs and wires(AC Delco), TPS, EGR, PCV, cleaned out the throttle body, and changed the coilpacks.

But it's *still* running terrible.

Oh and I do have an SES light. I took it to get it scanned and the 2 codes were "TPS relearn Incomplete" and "ambient air sensor". Neither of which I have no idea how to fix or replace....but I don't see how either of those could cause such horrible timing issues and backfiring.

Any ideas on where to look next?

Thanks!
-Chris

[kev's 96 Aurora]

could it be a timing issue?...not sure, belt slipping.

[ugsrich]

“TPS relearn incomplete.” There is a very definitive process following the removal/replacement of the Throttle Position Sensor. It involves running the vehicle at different speeds for different periods of time to “train” the computer. The entire “training” process is spelled out in the G-Body Service Manual. I’m not sure how or if that would create a nasty misfire. The ambient air temperature sensor is located just inside the main air intake at the bottom and in front of the radiator. I’m not completely confident that sensor alone would cause the nasty performance you indicate. Then again, once these modern engine control systems get out of harmony who knows.

What it sounds like to me, although you’ve got no “codes” to indicate it, is the timing sensor that detects the drive shaft position. I had nearly the exact same symptoms on a GM V6-3800. Ok idle, absolute crap acceleration (performed as if only one cylinder was firing) and included throttle body ignition of fuel that blew apart the air-cleaner housing. It was the timing sensor on the main shaft. I’ll dig into the G-Body manual more and see if there’s any diagnostic tree to further understand the potential cause and to clarify any terminology so at least you can “ride tall in the saddle” should you need to interface with a service technician.

[kev's 96 Aurora]

also..one thing I have seen before is the firing order problem on another car..the car would idle fine but as soon as you tried to do anything it was crazy..you changed the coilpack correct..is it possible that the firing order or plug wires are on the incorrect plugs...i would think that the firing order is electronic so where they are connected would probably cause an issue if incorrect... dunno

[magyar]

Hi guys....thanks for the help. My engine was running bad before I changed everything I could think of. It actually runs maybe 10% better now than before I changed everything.

ugsrich-do you have these manuals? If so, could you get back to me on the TPS relearn procedure and anything you might think of?

Thank you guys!
M

[ugsrich]

Ok my friend here it is. As printed on pages 6E3-C-6 and 6E3-C-7 Book 2 of 2 1995 G-Body Service Manual. I typed it as accurately as possible. I MAKE NO GUARANTEES THAT THIS WILL SOLVE YOUR PARTICULAR PROBLEM. I MAKE NO GUARANTEES AS TO THE ACCURACY OF MY TYPING - I believe it to be accurate.

Here's the first part:

TP Sensor Learn Procedure
(Without Tech 1) 1995 Service Manual G-Body

A “TP SENSOR LEARN” routine has been implemented in the PCM software to allow the PCM to correct or offset the closed throttle signal value of the TP sensor. This is necessary because of manufacturing tolerances during minimum air adjustment, TP sensor manufacture and because the TP sensor is not adjustable on the throttle body. If an improper TP sensor offset is maintained by the PCM, a high idle at closed throttle or stall condition may occur. Performing the “TP SENSOR LEARN” procedure lets the PCM learn the correct TP sensor offset.

The “TP SENSOR LEARN” procedure should be performed when:

§ The TP sensor is replaced
§ The throttle body is replaced
§ The PCM is replaced
§ Before the “IDLE LEARN” procedure
§ If “TP LEARN” is reset

To perform the “TP SENSOR LEARN”:

1. Turn ignition to “ON” (do not start, engine not running)
2. Turn ignition to “OFF”
3. Wait a minimum of 20 seconds
4. Turn ignition to “ON” (do not start, engine not running)
5. Turn ignition to “OFF”
6. Wait a minimum of 20 seconds
7. Turn ignition to “ON” (do not start, engine not running)
8. Turn ignition to “OFF”
9. Wait a minimum of 20 seconds

Here's the second part:

Idle Learn Procedure
(Without Tech 1) 1995 Service Manual G-Body

The “IDLE LEARN” routine of the PCM calculates a throttle angle correction or offset that is used during closed throttle idle control. If an improper throttle angle offset is maintained by the PCM, a high idle at closed throttle or stall condition may occur. Performing the “IDLE LEARN” procedure lets the PCM learn the correct throttle angle offset.

The “IDLE LEARN” procedure should be performed when:

§ After the “TP Sensor Learn” procedure
§ The ISC actuator is adjusted or replaced
§ The TP sensor is replaced
§ The throttle body is replaced
§ The PCM is replaced

To perform the “IDLE LEARN”:

1. Start the engine
2. Allow the vehicle to idle continuously until the coolant temperature is 80C (176F), then idle an additional 5 minutes
3. With the transaxle in “PARK” range, briefly accelerate the engine over 1500 rpm
4. Return to idle
5. Apply the brakes and place the transaxle in “DRIVE” range
6. Idle the vehicle for 2 minutes or until the MIL (Malfunction Indicator Light) goes out

As I mentioned earlier. I had a similar condition and it was diagnosed to be the Crankshaft Position Sensor. None the less - Good Luck.

[magyar]

ugsrich- Thank you so much for all that info!!!! You are a Godsend!


BTW, do you have any idea where the crankshaft posistion sensor is located?

Thanks!
M

[ugsrich]

Man...if only women were as interested in the Aurora as we (guys) are - it would be so cool for them to think I am a "godsend"!

On to your follow on question:

At the risk of being called a wisenheimer - near the crankshaft. (Ok, call me a wisenheimer.)

Seriously, judging from the illustrations (I have not visually confirmed this) it is located at about the 3 o-clock position (looking at the engine from the passenger side) down near the harmonic balancer. It's pretty tight looking down from the top - you may need to crawl below to try get a visual. Look for wire-harness and connector tucked right in near the serpentine belt drive mounted to the crankshaft. (Am I making sense here?)

Good luck.

[abrigham]

my car just began doing the same thing....did u ever fix this prob...no ses light has come up on mines though

[magyar]

Originally Posted by abrigham

my car just began doing the same thing....did u ever fix this prob...no ses light has come up on mines though

I fixed mine 75%. I had a coil that was completely dead. I replaced that and now it runs ok. It only backfires when going up a big hill and while giving it a good amount of gas. It also is sluggish around town sometimes, but I just floor it and it gets power. But it's A LOT better than the way it used to be.

M

[abrigham]

the service center just called me and told me they are replacing all my plugs and wires and that oil was clogging something..maybe a coil i dont remember...they said it should be doon today so i'll be back later to tell you if they completly fixed it...all i konw is that for the amount of money i'm spending it better be fixed!

[Hesam]

Read my 6-20-04 advice post regarding plugs/wires