88 LE 112k - runs rough on freeway-FIXED!!!

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EDIT: Monday, April 14 - R&R driver's axle - all good. Heartfelt thanks to everyone who offered help. She runs so well now...

Hi again everyone,

This problem has been with me for awhile but it came slowly. Driving from Culver City to Long Beach on occasion, the car would start to run rough at 65 - 70 about halfway down - about 10 miles. When I started out it seems fine... smooth, the power is there. The problem doesn't seem nearly as noticeable in surface street driving, but it could still be there.

It's an '88 LE with 112 thousand miles. Oil has been kept up and filters. Transmission only has 37,000 on it, the tires are in good shape and don't appear to be out of balance - it seems like more of a vibration but it pretty much stops when I take it out of gear at speed.

As I said, it's gotten worse over time but changing the plugs only helped with low-end performance. - I found a vacuum leak to the throttle body but again, aside from an improvement in low-end performance, nothing changed.

I can do easier things like window regulator r&r but my sensor/fuel/electric diagnostic skills are too weak as of this post. I don't have meters and wouldn't know which ones to get/use or how anyway. But I'm willing to try as long as it's not too expensive.

If you need more information, please don't hesitate to ask and thanks for reading.

Mike
Los Angeles

[RJolly87]

If you are cruising, steady on the throttle (no cruise control), while the issue is happening, does the problem go away when you touch the brakes?

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Thanks for asking Randall. You've asked a question I can't answer... I'm thinking it's there if my foot is on the gas. When I take it off, there's less... I think of it as a foot-on-the-gas issue so I have to get on the freeway and try to find out.

Thanks for asking and if there might be anything else I can try in order to narrow the involved systems down, please feel free to make suggestions - g-rated if possible

Mike

[RJolly87]

Is setting fire to the car considered G-Rated? If so, we may be able to fill that in as a last resort...

The reason I asked, is because misfire issues typically surface the most when at cruising speed, as the torque converter clutch locks up, and it is one solid connection from the engine to the wheels. When you maintain throttle at cruise speed, and touch the brakes, the torque converter clutch should unlock. You will notice a slight raise in rpms with this, and it should re lock after a few seconds after letting off the brake (feels like a shift most times). Does this car have the LN3, or the old engine?

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fire - good.

I don't know if I have the LN3 or the older engine (almost certain it's a Vin C) - google isn't helping here much, either. The torque converter seal was replaced a couple years ago and (I'm not saying they're connected beyond more than having the same words in a sentence) but the vibration started just a while later. I also have a rattle I heard could be connected to a catalytic converter rattle - not saying they're connected either but I don't like to either hear or feel those things in my car - like a missing tooth. The cat rattle (if that's what is rattling) is really noticeable on start-up.

I'll try to get the freeway test done today.

[RJolly87]

If you think you hear a cat rattle, you should investigate that when the car is cold. If you knock on the cat, with like a rubber mallet, and it rattles, then it is broken and should be replaced.

No point chasing gremlins if there is one possibly staring you in the face.

[RJolly87]

LN3:


LG3 (old one):

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test results - while they're fresh.

1. Roughness most noticeable at around 65 - 75 mph.

2. Light braking - at speed - while holding accelerator steady, produces clear "shift" sensation. Roughness re-engages almost immediately on release of brake pedal.

3. Possible Catalytic converter "buzz" most noticeable cold or hot, 0 - 25mph while under "light" acceleration. I'll work on the percussion test soonest.

Mine looks (to me) like the older engine, but I have doubts about my id so here's a snapshot. Image quality isn't the best but my phone is my only camera so...

[img][IMG]http://i280.photobucket.com/albums/kk184/illegiblexl5/SSPX0035_zpsf813ddd4.jpg[/img][/img]


Thanks RJ,

Mike

ps - not sure how to get actual image into post, but I'm working on it.

[RJolly87]

That is actually the LN3, it is just missing the cover.

[ajla]

If it was mine:
I'd change the air filter and fuel filter. Clean the MAF and throttle body. Finally, run a bottle of Techron through it. Then see where that gets you. It's all pretty cheap to do (like less than $50).

If you accelerate up to like 80 and then let off the gas and let it coast to 60, how does it behave?

[Drive-In]

Hi ajla and thanks for your input. I was just reading an article here:

http://www.agcoauto.com/content/news/p2_articleid/203

(I hope putting a link here isn't against forum rules - lemme know if it is)

The torque converter seal was replaced 18 months ago and a transmission flush done around then too. I had some serious problems with the transmission as soon as I bought the car. Lately, it's started shifting from 1st to 2nd a little hard and some other sort of vague issues with shifting so it's time to look into the tranny again. RJolly seems to have been right on the money about what's called torque converter shudder - it seems to fit very closely and it matches some other issues with shifting and a kind of "heavy" feeling when I accelerate sometimes.

It doesn't seem to be missing or running rough at idle or lower speeds. Though I do need to go through it and clean up filters, wires, vacuum and so on. So any suggestions and how-to's like that are welcome.

Does anyone know where I can find the injector cover badge for the LN3 Vin C 3800? It appears mine is missing.

Thanks for reading,

Mike

[myfirstbonnie]

Fixed picture link



Check the vacuum modulator on the transmission. It is a round can on the front of the transmission just behind the radiator with a vacuum line going to it. Do you have a large gray one or a small goldish colored one. **Edit, I can see you have an old style modulator.** Will not hurt to put a new one in and it will be adjustable. One 10mm bolt holds it in and only a few drops of fluid may come out.

I also suggest replacing that magnavox coil set-up with the 3 individual coils and putting new plugs and wires in it. My 89 used to have the same shudder and it went away when I swapped the coils. It goes away when you touch the brake because the TC has unlocked and the misfires from the engine are not transmitted through the transmission as much.

As for the rattle, see if the cat has been replaced. When mine was replaced, it was not positioned right and at low speeds it would rattle the exhaust against the bottom of the car. When in gear, it would rock the motor just enough for it to touch just a very little. They just moved the cat back with a new extension welded in to put it in the tunnel where it was supposed to be.

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mfb, thanks for the info - I can use all of it

1. How did you get the image into the body of the post?

2. Do I need to stick to AC/Delco for my electronics? (at least where possible)

3. Money issues require prioritizing - looks like servicing the transmission is first, then coil packs and vac. modulator.

4. Fuel Injector cover badge - anyone have sources they're partial to? - ebay and junkyards are all I've got for now and I'd really like to replace that cover.

And thanks again for the assistance.

Mike

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Update:

Had a transmission shop test drive it today. He said engine misfiring is likely being amplified by the torque converter when it's at cruising speed. Suggestion was coil pack and wires first (plugs were just changed - slight improvement) then go from there.

He also said the transmission has either a busted spring or a stuck valve so shifting is impaired - which accounts for some confusion between running rough + shifting issues.

Money matters mean I've gotta wait a few weeks to get to the coil packs etc, but for those of you who've been helping, if it takes me a few weeks to make progress and get back to post results, please accept my thanks for your help.

"A'll be bahk."

Mike

[myfirstbonnie]

I would start with the modulator. It is around $20 and controls the fluid pressure in the transmission. Does the car seem to engage reverse with a lot of force or a bang?

The bracket, coils and ICM needed for the swap is cheap and easy from a JY. Usually $20-$40 and a direct swap. Go to the JY and tell them you need the parts from a 92- up Bonneville, Park Avenue etc. Some places will tell you they are the wrong parts, but we know better. For wires, get the Belden premiums from Napa. Lifetime warranty and good wires.

As for the engine cover, it has no real function, but the only place to really get one would be used, JY or another owner.

[Drive-In]

mfb, thanks for that post. Autozone has the modulator for $ 13.00. I haven't found r&r specs in my manual for it. Does it come out by removing a clip and twisting back and forth - installs in the reverse?

In re: ICM from newer models, what years and models are backwards compatible with the '88 LN3? I know GM put this plant into a number of models so maybe just the top five or something. Will help me narrow down JY searches.

Do I need to apply heatsink compound when I re-install the ICM and if I put new coil packs in, are there any specifics that are different than the '88's LN3 coil packs?

Again, thanks for the help - it's really appreciated.

Mike

ps - the engine cover is a vanity must-have. but without thee feelthy lucre, i guess i'm just gonna hafta do without

[myfirstbonnie]

Modulator is a single 10mm bolt. Remove bolt and bracket. Pull out old one. Insert new one and replace bolt, bracket and vacuum line.

For the ICM and coils, on the LN3 they are a direct swap. Just make sure the plate is free of corrosion. There is also a couple ground leads held on by the bracket. Make sure they are clean and making good contact. Funny things happen when those are not making a good conection.

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Took a minute to look things over and combined with your tips, everything looks really straightforward.

Any advice on r&r the stereo? I took the radio out today. Most of the speakers too... Head unit's mostly d.o.a. Speaker's are pretty solid... one's in the trunk are 48 ounce Cerwin Vegas No Bose, no steering wheel controls to deal with. Anyone have any dealings with Crutchfield?

Thanks again mfb - big help.

Mike

[SSEBonne4evr]

try cleaning the egr valve.

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SSE, thanks for the advice. Can I ask why clean the egr if I'm not throwing and code and my emission test come out clean?

Mike