Contour Enthusiasts Group Archives Forums General Troubleshooting Gathered OBD-II data on my car - need info

Background: My car (1998 Contour / Zetec / MTX) has developed a bucking/stuttering problem. It's driven me nuts and I finally got some info that may lead me to a fix. However, I need the help of someone that understands the Ford computer better than I.

I went down to StreetFlight and used their OBD-II scanner and compared every PID it gave me against what is listed in the Diagnostic Reference Values table on the Ford Diagnostic DVD.

Almost everything is within parameters. However, a few things leave me scratching my head (this data was gathered at Hot Idle):

OCTADJ - CLOSED (Mine was OPEN)
SPARKADV - 15-25 degrees (Mine read 28-29)
TPREL - Not listed in the chart (Mine read 0.88 volts
IMRC1M - Not listed in the chart (Mine read 1.88 volts

Why is my OCTADJ open? There's an octane sensor, correct? If it were failing, is it safe to assume this would affect the SPARKADV?

In the grand scheme of things, is 3 or 4 degrees SPARKADV beyond tolerance a large enough variance to cause a problem like mine?

What is an acceptable voltage for TPREL at Hot Idle? For that matter, what is TPREL? I could only guess Throttle Position RELease (don't laugh, best I could come up with).

Same question for IMRC1M...what's an acceptable voltage and, being a 4-cylinder, should this even come up?

Other than those items, everything else was on the list and/or within parameters.

In case you're wondering, we ran several other checks before pulling out the OBD-II. Differing fuel pressure tests. Vacuum tests and a couple other items I don't remember. Everything seemed fine from what we could tell

Anyone have any ideas??

According to the Vehicle Explorer OBD-II scanner software that I have:

TPREL=Lowest steady TP voltage since engine start (RATCH)(0-5.0 volts)

It doesn't have IMRC1M, it only has IMRCM and IMRC2M, so I would guess that IMRCM is the same as IMRC1M.

IMRCM=Intake Manifold Runner Control Input Bank 1 voltage (0-5.11 volts)

I found the following articles on the web related to spark advance:

http://www.grubinski.com/grubinski/59.pdf
http://www.howstuffworks.com/ignition-system.htm

I also found the following in the Ford TSP CD:

The Octane Adjust (OCT ADJ) shorting bar is used to retard spark timing. Removal of the shorting bar from the in-line connector will typically retard spark three degrees. The purpose of the OCT ADJ self-test is to check the state of the OCT ADJ shorting bar. A Diagnostic Trouble Code (DTC) will be present if the shorting bar is removed or if there is an open circuit. The OCT ADJ shorting bar is similar in shape to the SPOUT in-line connector. On some applications the PSP circuit will also have a similar shorting bar connector. DO NOT remove the shorting bar unless directed by a Technical Service Bulletin (TSB).

The Flexible Fuel (FF) sensor is a capacitive device with a signal processing stage whose frequency varies with the dielectric constant, conductivity and temperature of the fluid medium (methanol-gasoline mixture) in its measuring cell. In general, as the percentage of methanol in the fuel mixture increases, the output frequency of the FF sensor signal will increase. For example, a fuel mixture that is 30% methanol will have a FF sensor signal output frequency between 60 and 100 Hz; 60% methanol will have a FF sensor signal output frequency between 90 and 130 Hz. The PCM uses the percent methanol information to calculate the correct air/fuel ratio and spark advance for the vehicle.

The Knock Sensor (KS) is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and to retard spark timing.

A few things come to mind:

What RPM does your car idle at? If you car is idling above normal, then I would think the spark would advance to compensate for this.

How many miles do you have on your car, and when was the last time you changed your spark plugs? Also, what spark plugs are you using?

What octane gas do you use?

I use 87 mostly, but occassionally throw in a tank of 89 or 91. I try to use only Chevron gas.

I last changed the plugs around September. I use Autolite Double Plats. I changed the fuel filter at the same time, and the wires were replaced early '02.

The car has 103.5k miles on it. My tach shows idle at about 800, but the RPMDES showed 896.

A few things I've considered as causes are:

TPS
Mass Air Sensor
O2 (upstream is fairly new - downstream, maybe?)
Coil
Knock Sensor
cat.
Timing
Fuel pump

Aside from the Coil and the cat. (which I don't know how to check), everything came out w/in parameters, with the exception of the spark advance and the octane adjust.

I read the URLs you posted. I'll be loving life if it's just a bad knock sensor, but things usually aren't that simple for me

You might want to check static timing to make sure the timing belt has not jumped. You have replaced it haven't you?

Yeah, I had it replaced back around 75k miles.

By static you mean w/ a light?

No, I mean line up the timing marks on the cams and crank.

Did you replace the tensioner, or have you heard the belt flapping around?

Might want to check that TPS with a meter.

Are you sure it's the engine? Weak clutch springs and a glazed flywheel can buck on engagement and throttle change.

Roger, it's funny you should mention static timing because, even though I didn't know that's what you call it, I was in the middle of that when I read your post about it.

During the summer I had the timing belt tensioner replaced under warranty. That's the same time I had them replace the belt. One thing we noticed yesterday was how loose it was.

We re-aligned everything last night. Now, the car is definitely running better and the timing belt is on tight as hell

So, thanks for the reply, because that was a big part of it (the cams were far enough out of line we couldn't get the cam alignment tool in both notches at the same time until we removed the belt ). Now the car is running much better. I have a CEL, which I attribute to us turning up the fuel pressure Fri. night (I have an adjustable FPR). I turned it down to where I think it was, but w/out a pressure guage, I can't be certain. I'll have to drop by SF tomorrow and double-check it.

I'm sure the clutch isn't helping. I think I hear the throwout bearing rattling slightly when the clutch is out. However, the hesitation existed even w/ the clutch in.

I'm down on power a little, which I again attribute to the CEL. Once I nail that down, I should be good as gold.

I also pulled the fuel pump today to inspect it. Clean as a whistle.

PS - we did check the TPS w/ a meter Friday night. It seemed to be a little out of phase, but it isn't expensive to replace, so I'll likely order one this week or next just to be sure.

Result: Hesitation/stuttering gone!!!