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

[SSEBonne4evr]

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

Your IAC valve adjusts based on the intake air pressure, a leaking EGR could
skew everything including the timing.
Just a thought.
Have you also checked the TPS readings?

[Drive-In]

SSEi, thanks for that. Since I've just gotten started turning the bonnie into a project, my current learning curve looks more like a wall at the moment.

So far, I'm starting with the vacuum modulator (rough shifts and high-speed misfires) and the coil packs/ICM. Money's an issue along with skills with a meter (beginning). So, most bang for my buck for the next couple of months.

To be honest, troubleshooting the IAC or TPS accurately is more than I think I might be able to do over the next few days. I do have a sense that at 112k, the sensor system could stand a thorough going-over.

Oh, before I forget, I saw a post you made of parts you have available. You don't have the LN3 engine cover badge by any chance, do you? My bonnie didn't come with one and I'd like to replace it.

Thanks again for your effort,

Mike

[Zeik75]

I wouldn't replace any sensors until you do the updated coils. Simply because I wasted a LOT of money on my 88 not knowing any better. I tried replacing the TPS, MAF, Cam position sensor, and the Magnavox style ICM i think 4 times after the original went bad before I did some searching and was told to update to the new style with the 3 coil packs. Ever since she has ran much better....until the transmission started its decent into implosion. Anyway after that I would replace the modulator on the tranny if the vacuum hose is good still (no cracks).

Also is the tranny you have a rebuilt one or a used one that was put in? If it was rebuilt i wouldn't think you should have any internal mechanical problems, they are pretty solid IMO, with as hard as i drove mine it has held up like a champ for almost 180k. I wouldn't do anything drastic like drop the pan on it or anything till you try the easy stuff out.

p.s. Junkyard parts seem to be more reliable than the "cheaper" aftermarket ones also, especially sensors.

Good Luck!

[Zeik75]

Also any stereo questions i would be happy to help with. I did a lot of work to mine and have had it apart and together multiple times. Just give me some specifics and I'll tell you what i know.

[Drive-In]

Hey Zeik and thanks for the help.

Not sure where to start but - I replaced the vacuum modulator with the newer version and it was a big improvement in shifting and related things. But the misfire under load is still with me. Money's an issue right now but I was headed towards trying to find a 93 - 95 ICM or just buy one but they're a little pricey.

I've read the TPS can also be a culprit as well as injectors/injector electrical and other things. The transmission was rebuilt and only has 35k on it but when it was rebuilt, it had to go back five times for them to get it right. I took it to a different shop a couple days ago and (this guy rebuilt a trans for me in a 87 buick skylark and did a great job) heard the hard shifting is either a broken spring or a stuck valve - $ 2,000.00 either way. He said to just keep driving it.

I'm tempted to locate an expert diagnostic shop just so I don't have to throw parts at the silly thing. It's not in that bad a shape and I'd like to get it fixed.

Anyone have any input on getting a shop to realistically troubleshoot a misfire under load? It might be asking a lot but if they were straight shooters, it could save me some money in the long run.

As for the stereo, that's probably gonna take a couple months for me to get to so no hurry.

I'm also looking for the LN3 engine cover badge in case anyone knows where to find one.

[SSEBonne4evr]

Misfire under load is usually a bad coil or spark plug wire.
Have you tested the coils and replaced the wires? - sorry long read.

[Drive-In]

SSE - thanks for your help. I haven't tested them, partly because I don't know how (I'll research today) and partly because I was going to just replace them both when the money comes in (two weeks).

The wires are maybe 2 or 3 years old. But the coils are likely 25 years old.

I'd like to swap the whole thing for the 93 - 95 assy but I'll have to wait.

It is too long of a read but thanks for your effort.

[Zeik75]

Do you have access to a junkyard nearby? If so you should have no problem finding a series one 3800 to rob coils and the icm from. Whenever i go to my small one even there are usually 15ish series ones and 10-15 LN3's to pick from. I can dig up the vin for cars with the swappable coils if you need.

[Drive-In]

I can dig up the vin for cars with the swappable coils if you need.

Hey Zeik - thanks for that. Is there a way to use google to identify compatible vins? How do you do that - maybe I can learn how to snipe parts from several different vins that way. Let me know.

[Zeik75]

Well the 8th digit of the vin number designates the engine. I believe the series one non supercharged is vin L. You can read the vin through the windshield on the bottom of the drivers side. As far as google i'm not sure if you will find any info about compatible vins or anything like that. you would just have to do some searching.

If you look up Buick 3800 v6 and go to wikipedia it will list all the cars the engine came in.

[Jrs3800]

I can dig up the vin for cars with the swappable coils if you need.

Hey Zeik - thanks for that. Is there a way to use google to identify compatible vins? How do you do that - maybe I can learn how to snipe parts from several different vins that way. Let me know.

Read this
http://www.pontiacbonnevilleclub.com/fo ... c1684.html

[Drive-In]

Jrs3800, I can't believe I didn't say thanks for this the instant I saw it. Thank you. It's a great post. (I can't think straight so pictures really help )

I went with an AC Delco replacement Magnavox coil pack (Summit Racing $ 108.00) for ease and speed. The car runs MUCH better at idle, acceleration and at freeway speeds. Power and response are a joy once again. But...

Now that it runs better, it's easier to feel both the tremble in the idle and the "misfiring" on the freeway. I even notice it when I release the gas pedal (at 65 - 70 mph) and coast, it still "runs" rough. Almost as if it were the transmission. I lightly touched the brakes to release the torque converter, but no change.

I'm going to look into troubleshooting the injectors but something tells me it's in the power train somewhere. Do you guys have any thoughts?

Replacing the coil pack (even with a new but outdated one) breathed so much life back into that engine, I was shocked at the difference. As money allows, I'd still like to replace the wires and a couple of the sensors - but I really do need to correctly diagnose the rough running... I just haven't earned the bonnie's respect yet so she won't give up her secrets... but I will.

Thanks for reading and for your help.

Mike

[Drive-In]

Hi all,

Update:
So far, I've replaced Plugs, Wires, Coil Pack (not upgraded with ECM/Pack from the 93-94 3800), Vacuum Modulator and O2 sensor.

Great performance increase with Vacuum Modulator and Coil Pack replacement. The rest helped, I'm sure - but I still have the rough running at freeway speed - more noticeably after 10 miles or so. Also, taking my foot off the accelerator does NOT reduce the vibration. So now I'm not sure if I'm dealing with engine performance alone.

Would anyone suggest I get an engine analyzer and start eliminating components and sensors? If so, can someone suggest an analyzer under a $ 100.00? I'm not going to throw in the towel. The few things I did had a huge impact on performance. I just need to go deeper.

Thanks for all the help so far.

[Zeik75]

The o'reileys in my town has a scanner i can borrow for mine to pull codes. You could try that and see whatcomes up. Otherwise I don't have or know of a scanner for under 100

[Drive-In]

Hey Zeik, thanks for the tip. What I was just able to do was, using 93RedSled and Jrs3800 diagnostic pages, short my PCM and pull codes. I found out the diagnostics do seem to be working and I pulled out a code 42 - Electronic Spark Timing Circuit issue.

A quick google indicates it could damage my catalytic converter (which started to buzz around the same time it started running rough on the freeway.

So...

Electronic Spark Timing Circuit, eh? Ok... I'll bite: "Duh, what's that?"

Off to find out - will post when I do.

[Zeik75]

It is the circuit that controls timing based on engine speed. Basically the CPS (Camshaft Position Sensor) is a sensor bolted on the front cover that triggers when a magnet on the crankshaft timing sprocket passes it. The computer uses this to determine the rpm's that the engine is actually spinning at and is supposed to send the signal to the ECM to determine timing of the spark.

What your car is doing instead is not sensing the magnet so It doesn't send a signal for the ECM to determine timing. This means that the C3I module controls the timing instead, which I believe makes the plugs fire in the correct order, but not correct time. (they can either fire earlier or later than they should REALLY be firing).

In simpler terms your magnet is held in a little plastic clip thing. This clip has broke and the magnet is probably stuck to the engine so that it can't trip the CPS. You can test this by removing the CPS, it should be up and to the right of the Harmonic balancer, and looking in the hole while manually rotating the engine so see if the magnet is there or not. If not you have found your problem and you just need to put a new magnet in. that however requires removal of the front cover which can be a task the first time around. I believe some people have gotten by with glueing a new magnet onto the plastic clip though. it could be worth a shot.

[Drive-In]

Zeik,

Ok...

Took some time to digest both your post and what the manual seems to be saying. What I've come up with so far, is this;

1st. I can replace the camshaft position sensor myself, provided I don't have to remove the waterpump pulley.

2nd. I won't replace the crankshaft position sensor myself. Lack of experience and the proper tools can result in costly mistakes.

You seemed to say in your post I can troubleshoot the crank sensor by manually advancing the crank to see if the magnet appears in the port. I have to get in there first and I'm not sure I'm going to go that far on the crank sensor. It looks like the cam sensor can be R&R'd just by moving the belt out of the way and taking out one bolt. Does that seem right to you?

1. I'm almost convinced it's one or both of those sensors - but I'm not sure.

2. Before I replace the cam sensor myself and have a shop do the crank sensor, I'd like to get a little more confirmation. Any suggestions?

Huge thanks for your help.

Mike

[Zeik75]

I believe it is actually neither sensor, but a magnet on the timing chain sprocket inside the front cover. I will have to take some pictures tomorrow of my spare parts to help better understand.

[Drive-In]

Zeik, thanks for your time.

Noob questions (2 or 4, maybe 5 or 8)

What's the difference between the ECM and the C3I?

CPS is Camshaft Position Sensor or Crankshaft Position Sensor?

The magnet is part of the Cam Sensor or the Crank sensor?

The cam sensor is left of the water pump and the crank sensor is right of the Harmonic balancer.

Is there a chance that, when I went off-roading, a rock came up inside the engine bay and kwanged into one of the vanes on the harmonic balancer and when that vane passes through the crank sensor hall switch, it reads wrong?

Mike

[Zeik75]

Sorry I didn't realize CPS could work for both LOL.

I was meaning Cam position sensor. This is a L67 front cover but the locations are the same for Cam and Crank sensors.

This is the Cam sensor hole. The sensor that mounts here reads the magnet when it passes.


This is the crank sensor


The only difference between this cover and yours is that your 88 will have an adjustable Crank position sensor. It isn't too hard to line up IMO though.

This is the timing chain that lies under your front cover. The small sprocket mounts on the Crankshaft and the large ones mounts to the camshaft. The round hole is where the magnet mounts.


This is the magnet that mounts there


This Is on an L67 still the same thing really. The engine is upside down in this picture though


I'm not 100% sure on the ECM vs. C3I, but my best understanding is that the C3I is the modual used for Starting because it has a set spark timing that will NOT adjust to engine speed. The ECM is what the book calls the ICM (ignition control modual which sits under the coils)

Yes the Cam is to the left and down slightly of water pump. Crank is to the right but also under the harmonic balancer so it must be removed to change the Crank sensor.

I highly doubt that a rock got between the Harmonic balancer and engine, It could happen but it would have to be very small and It would break the plastic sensor before it messed up the vanes. If the sensor were broken like that though I don't believe the engine would run at all.


If you determine that the magnet isn;t there ( the plastic there usually gets old and brittle and the magnet gets flung off and sticks to the engine somewhere) then you should be able to just break the old plastic that is left. That will fall straight down into the oil pan. then insert a new magnet, it just clips in so it shouldn't be too hard. That way you don't have to pull the Front cover and you can just drop the oil pan to remove the plastic. This is just an Idea and I have never done it but i see no reason it won't work.