'97 GLT grumbly on cold mornings

[Chuck W]

So, I've been investigating this when I have time.

Her car, while starting just fine, misses a bit and doesn't rev clean until the motor gets a little heat in it.

First suspect to me would be the ECT. It's not that old, but I checked it out on a cold engine one morning through the 850OBD-II app, and it was within a degree of ambient. I unplugged it, and it registered -47*, so I think the sensor and wiring are good.

Once it is warm. it runs smooth and fine. Has plenty of power. Mileage has been good/par for the course.

As a refresher on the motor. It is an '01 LPT RN motor, with currently disabled exVVT. It's running on the DIY M4.4 conversion with some of Aaron's code, but I haven't changed any of the tune in months (well over a year).

Plugs and coils are less than a couple years old. MAF is a couple months old. Swapped in another (repaired) FP relay, but it didn't change anything. It fires up right away anyway.

I could change out the ECT as a check. as they're not that expensive, but I'm not sure it's the issue.

I haven't checked FP, but again, no signs of the system struggling under any load, etc.

A couple variables in the mix. Is the VVT pulley failing? It's not activated currently, and again, the car drives fine otherwise. I know the car is in need of valve seals, but any of that contamination should clear up within seconds, I would think.

Anything I'm missing?

[scot850]

Leaking injector? Have you checked for a puff of black smoke when starting? Sure that could also be leaking valve stem seals.

As yours is a newer engine you won't have the air valve. Throttle body issue?

Neil.

[Chuck W]

Leaking injector? Have you checked for a puff of black smoke when starting? Sure that could also be leaking valve stem seals.

As yours is a newer engine you won't have the air valve. Throttle body issue?

Haven't noticed any black smoke, but haven't been on the lookout, either.

No e-throttle on this car. Running the '97 intake/tb.

[MoVolvos]

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Unplug each coil in the morning when it's grumbly. The good ones will make it even worse but I'm preaching to the choir.

I had two 3 cracked coils that eventually set codes and the grumbly became angry. Prior to that it would drive grumbly with less power before warming.

Next is clean the ETM. After replacing the 3 bad coils and cleaning the ETM the car smoothed out when cold and power normalized. You can CIP, clean in place. Use a lint free smooth rag. No paper towels. Spray on rag and into the ETM. Will stumble quite a bit on initial start after cleaning.

That grumbly though not severe dogged me for about a year till I washed the engine and water seeped into the cracked coil housing and quickly killed one and started the entire diagnostic process.

Replacing the upper engine mount was icing on the cake in terms a quiet interior.
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[Chuck W]

There is no ETM on the car. RN longblock with N accessories, which includes the cable-actuated throttlebody.

By grumbly, I mean it doesn't really miss/stumble at idle, but more pops and missed when revving the engine a bit (with no load). The idle is a little off, but it's only perceptible to me because I'm used to how the car sounds when "clean".

I can recheck the coils, but they are not that old and checked out fine when I did the plugs earlier this year.

I'm going to try and get a datalog this week to see if anything stands out.

[MoVolvos]

There is no ETM on the car. RN longblock with N accessories, which includes the cable-actuated throttlebody.

By grumbly, I mean it doesn't really miss/stumble at idle, but more pops and missed when revving the engine a bit (with no load). The idle is a little off, but it's only perceptible to me because I'm used to how the car sounds when "clean".

I can recheck the coils, but they are not that old and checked out fine when I did the plugs earlier this year.

I'm going to try and get a datalog this week to see if anything stands out.

Right, forgot my 98 S70 T5 had a cable for the TB. Shouldn't you have a cap and rotor instead of coils though?
.

[Chuck W]

Right, forgot my 98 S70 T5 had a cable for the TB. Shouldn't you have a cap and rotor instead of coils though?
.

Nope. Converted to COP.

[scot850]

I had a set of IPD 'HD' coils and one failed after about 2 years and less than 3000 miles of driving. My buddy fitted an Napa coil when one on his car failed and it failed again within 2 years.

Coils start to crack on the opposite side of the coil body from the connector below the boot. It will then continue to spread from there. They then start cracking on the right side from the connector and that crack eventually allows the coil to short if the first one doesn't first.

Are you getting any pending codes?

Neil.

[Chuck W]

No codes, whatsoever.

[Chuck W]

OK. I had a couple minutes the other night so I made a quick change to the tune. I looked back at the repair log on the car, and I had a note around late October of last year about the car running rough on start-up.

We're running greens on the car, and there are a couple "Injection Basic Adjustment Factor" values that have been tossed about on the forum. I'd had the slightly "bigger" value in there, but changed it to the other, more used value.

It was 30*F this morning and the car ran better right at start up. Still a slight miss, but nothing like it had been.

The value I had in there making it think there were slightly larger injectors installed, and thus was probably a bit lean on the start/warmup. Switching the constant shifted things a little more "rich". Going to give it a couple days of driving to settle and get a data log. See what the mass air flow is and check the LTFT's. We might have a small vac leak that aggravates things until it warms up a little.

The car has yet to throw a code since I replaced the MAF sensor back over the summer. And that had been the ONLY code we had gotten for a long time.