CMP question

footee · Jul 10, 2016

I have a 96 3.0 that I was changing the clutch out of. When I was getting to the top bolts of the tranny, I noticed the CMP was very loose, kind of floating in the hole, which explained the oil pressure drops with the ac on and at idle. Anyway, I then pulled it out and replaced it following all the procedures. My question is, what are the symptoms if it's just like one tooth off or something? When I started it and drove it, it ran terrible for a little bit then seemed to relearn the pcm to the new part and ran fine. Now, a week later, it seems to do the same process of running like crap then boom, good and runs great.

I also replaced plugs (which were very worn) and wires. No CEL has been on before or after replacement.

RonD · Jul 10, 2016

The Cam position sensor is there to fine tune sequential fuel injection timing and spark advance.

Crank position(CKP) sensor behind crank pulley is the main sensor for spark and fuel injection timing, engine won't run without it, about the only sensor that can cause a no start.

If CPS(CMP) was too far off then computer would ignore it and set a code.
I have read that some 3.0l computers will not allow startup if there is no CPS pulse, CPS synchro shaft does drive the oil pump, so maybe that is why, no CPS pulse assumes no oil pump so no start.

Computer can tell how much power is being added to the crankshaft when each cylinder fires, by increased speed of crank shaft between pulses from CKP, so it adjusts the CPS signal it receives for best power and economy.
It also uses the CPS to help detect misfires since there it a pulse lag that is more pronounced, because of timing chain, on a misfire, adding power keeps chain tight, misfire causes momentary slack in chain which slows cam and CPS.

But I don't think that is causing your problem, because it wouldn't come and go.
Is the issue related to temp, cold engine warm engine?

Because I assume it ran fine until the CPS swap, what other wires needed to be moved or pulled on when doing the swap?

Or vacuum lines?

footee · Jul 10, 2016

I decided to put my scanner on it just to see... As it turns out, evidently my CEL doesn't work. I got codes p0353 p0135 p1131 and p1151. I cleared the codes and they didn't come back, yet at least. The KOER test did show the 1131 and 1151 still. I will add that I removed the exhaust when I did the clutch and didn't replace the gaskets to the manifolds. There is an obvious slight leak there and/or after the cats.

It only runs bad when the engine is cold. It's a good 85 degrees with tons of humidity here.

RonD · Jul 10, 2016

p0135 means O2 sensor wasn't reading correctly based on engine coolant temp.

And rough running while cold could be the same issue.

ECT(engine coolant temp) sensor is a 2 wire sensor on the lower intake near thermostat housing, only the computer uses this sensor.
There will be a 1 wire SENDER near it, that is for the dash board temp gauge only.

Find this sensor and make sure connector is good, unplug it and plug it back in.

When an engine is cold it needs extra gas, that's what the Choke was for on a carb, and thats what the ECT sensor is for on Fuel injected engines, when ECT shows cold the computer runs a richer mix so engine can run smoothly.
As ECT sensor warms up computer starts to lean out the mix.

O2 sensors can't work under 650degF, thats why they are heated and thats why the computer IGNORES them when engine is cold, and computer knows engine is cold based solely on the ECT sensor.

ECT sensor gets 5 volts from computer, if it sends back 3volts computer knows engine is cold, this 3 volts will start to drop as ECT sensor warms up, when engine is at 195degF, fully warmed up, ECT will be sending computer .5volts, under 1 volt.

If ECT connection is not tight or corroded computer may be seeing 1 to 2 volts on cold start, so it thinks you are just restarting a warm engine.
Fuel mix would be too lean, so rough running, and when computer "looks" at O2 sensors it sees they are not working very well(under 650degF) so sets some codes, lean because it is for a warm engine and O2 codes because they are not warm.
And as the engine warms up it would start running better because fuel mix is now correct for warmed up engine, and O2s start working

Not saying this is the problem, but given the posted codes I would check it out

adsm08 · Jul 10, 2016

I can confirm from personal experience the no-start due to lack of a CPS signal.

footee · Jul 10, 2016

It starts and runs fine, then when it idles down, and seemingly down to about 700 rpms, it's rough, kind of like a cam lope. I just started it again after sitting for a few hrs, same thing, then after it idled for about 5 mins, it cleared itself up again and went back to the 950ish idle. Still no more trouble codes. Smells like it's running rich, exhaust wise.

I checked the ECT sensor, everything seemed fine there. I was never working in that area so to me, it would be odd for that to suddenly be bad, even if the symptoms describe that.

I actually didn't hear any exhaust leak from manifold to y pipe, seems the only leak is from post catalytic converter to tailpipe.

I do want to emphasize, when installing the CMP assembly, I followed the instructions for tdc so I THINK I got that right. I THINK I lined the CMP up properly. Is it safe to assume it is installed properly? Meaning, if it's off just a little bit, would it cause these symptoms?

footee · Jul 10, 2016

Also, might I have damaged any of the o2 sensors when fighting to get the y pipe out and back in? The wires look fine. How fragile are the insides of o2 sensors?

footee · Jul 11, 2016

I pulled the CMP out and moved it one tooth back. I started it and let it idle for a few minutes and it no longer did the lope at idle that it did before. However, the timing chain slap/tap that is notorious on these engines seems worse than it was when it was set before. I may just be imagining it but all I can say is that, so far, the issue is fixed. I'll let it cool back down and try again later and see what it does.

footee · Jul 14, 2016

I'd like for it so be known that the issue did come back. I decided to change o2 sensors just because that's the only codes that ever came up. As it turns out, one of my upstream sensors was in fact broken. After a few cycles now, the old sypmtoms have not come back.

I am debating whether to put the CMP back to the other position or not simply based on the timing chain slap that's more pronounced now than was before. Any input?

The two tech articles say different things as far as TDC placement so I'm still curious as to the effects of being one tooth off of alignment to the cam.

RonD · Jul 14, 2016

Never heard or read about 3.0l having any timing chain issues generally, tensioners can fail just not common on 3.0l as far as I know.

The computer adjusts CMP signal for best power so I wouldn't change it unless you want to, and you would certainly get a Code if CMP signal wasn't close enough to CKP signal

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