88 LN3 Vin C Still runs rough under load

[Drive-In]

I've replaced plugs, wires, coil, ignition module, vacuum modulator and O2 sensor and she runs MUCH better.

But she still runs rough on the freeway after she's warmed up.

I'm looking into OBDI scan cable/software but I can't find definitions for the 88 LN3 Vin C.

Would I do better getting a meter, learning to use it and checking TPS, IAC, MAF etc. sensors as well as the injectors?

For the folks who've put time into helping me get this far, a great big THANK YOU! I'm wondering about the Cam Sensor Magnet, the timing chain assembly and fuel flow, but I can't throw any more parts at it.

Mike

[grant111]

Have you looked to see if the magnet is still attached to your cam gear?

Http://www.troublecodes.net/GM

Use a paperclip to jumper terminals a and b.

The first code you will see is flash, flash - flash (= 12). It will repeat this just means the computer is running. My guess is that you will get a code 41 next.

* = flash of the check engine light
- = pause

* - ** * - ** (12)

**** - * **** - * (41)

[grant111]

http://padgett.performanceresearch.us/cars/cammag.htm


This page will show you how to inspect the magnet (which I sincerely believe to be your problem), and how to replace it without removing the timing cover. You just trim some plastic from the magnet and JB Weld it into place through the hole where the sensor goes.

It's a $14 job. I have done this in the past and it worked fine.

[Drive-In]

Hi Grant - thanks for your help

I had a code 42 set before I replaced the ignition module but it's gone now. (I learned how to jump A and B and retrieve codes recently)

I have a new Cam Sensor which I haven't installed yet. I'm under the impression a bad magnet will set a code 41 if the signal is weak, or if it's failed, the car won't run. But there are no codes set.

I've got Padgett's how-to on gluing a magnet in but frankly, I'm getting frustrated with fixes that miss the mark. I'd like to find out just if/where I've got bad signals and go from there. You have any thoughts on how a weak magnet would fail to set a code?

Mike

[grant111]

Mike, my car ran rough only at highway speeds with no Manet.
I suggest that you look through the sensor hole and make sure there is a magnet there. I can't imagine a weak magnet scenario.

[Drive-In]

Hi again Grant,

Sorry to sound so peevish on my last post :/ I'm going to do a visual check as soon as I can get to it. The roughness I get is a very rapid pulse - like once per revolution of the crank - that's partly what leads me to the magnet also. It's gotten worse over the last couple of months which confuses me (as well as thinking if the magnet were gone, the car shouldn't start - but I'm not that good a mechanic).

Thanks again,

Mike

[grant111]

Mike - I went through my magnet issue almost two years ago now, but can clearly remember the torque converter locking questions, replacing sensors, general confusion and frustration. I replaced the ignition module and coil packs as well... Turns out that I also had a bad ecu, (quad driver module failure). Anyways... I see that you have been struggling with this for a while... The ecu remembers the last reading from the crank sensor and then goes into a limp mode after battery disconnect from what I can tell. But I promise the cal will start and run with no magnet. It will shudder at hwy speeds from my experience.

[Drive-In]

Hi Grant - thanks for the encouragement.

Magnet's good. Completely intact and still holding a strong magnetism when I put a small screwdriver near it. I replaced the Cam Sensor but I haven't road tested it yet.

You know, the symptom does remind me of something like a magnet going around the cam sprocket might make. It's almost a vibration at that speed, but it's slowly getting worse over time and with use.

Before I replaced the Vacuum Modulator, I took it to a trans shop. Guy told me it was a busted spring or a bad valve ($ 2k to fix). Vacuum Modulator (the one for the '92) really fixed the problems but I'm starting to wonder if the problem isn't in the transmission somewhere. I'm out of ideas at the moment.

Good workout if nothing else. The belt tensioner was a bear.

Mike

[Zeik75]

Hey sorry I didn't get back to you on the other thread, my email notification thing is messed up for some reason.

Anyway a thought just occurred to me by reading your post. You currently have no codes, the magnet is fine, and the shudder has slowly gotten worse correct? If so you could check the harmonic balancer to see if it is all cracked and missing chunks of rubber, also check both front wheel bearings. I had a wheel bearing go out recently and it had a shudder that matched my speed as it died. It might not be since you said your shudder matches RPM's, but it is very easy to rule out. Just set the parking brake, raise the front wheels and grab the edges of the wheel and wiggle. if it moves when you hold top and bottom the bearing is going bad, if it moves when holding left and right the tie rods are bad.

At this point I doubt it is an electrical/sensor problem and more like something mechanical is worn out. I'll keep thinking about this and see if i can come up with something else, but for now at least you can check these things for free.

And no haven't had snow up here yet, but it's not far off.

[J Wikoff]

While you're cruising and can feel the hesitation/roughness, downshift to third. Does the roughness change with the RPM or stay the same?

[Drive-In]

Hi guys - sorry to delay getting back to you, I forgot to subscribe to the topic. fixed.

A little clarification - could be important. When the car is warm and I'm stopped at a light, the idle stumbles. It's not rough or anything like it, but it's definitely not smooth. Then there's the roughness at freeway speed which even continues after I take my foot off the accelerator (I can't really tell if it disappears when I touch the brakes because it never really seems to go away until I slow down below 30 or 40 mph).

Last check for codes (my CEL has never come on... ) But as of Thursday afternoon, after I replaced the Cam Sensor, there are no codes currently set.

Will road test today and try the downshift. I'll also try to get it raised and check the bearings. Zeik, there's rubber on the balancer? I'll take a look at it, see if anything weird shows up. EDIT: Test results:

1. Vibration starts at 45. Either in 4th gear, if I downshift to 3rd or if I accelerate up to 45 in 3rd. It's consistent. It vibrates at a certain frequency and the frequency does NOT change as I accelerate. It becomes more intense but not faster or slower, up to about 60 where it levels off. It continues when I coast back down to about 40 or 45 where it disappears into routine road vibration.

2. I feel it in the seat and the floor pan but not the steering wheel.

3. There is NO play in the front wheels. None.

END test edit.

If I get a blowtorch, cut off the tip and connect a length of rubber hose, is that a good (safe enough) way to check for vacuum leaks? A big fire might make things worse...

Mike

[Drive-In]

It's the transmission. Had it on the freeway today and, at speed, put it in neutral (it slowed noticeably, rather than coasted) and when I put it back into gear, there was no connection. Not in drive, or 3rd or 2nd or 1st. I coasted off the freeway and managed to slide into a small lot. When I put it back into gear, it went just fine. Finished the trip down and back and though it's running even rougher, there were no more incidents with the transmission. Knowledge is power... I just wish the knowledge included transmissions.

Thanks for your help guys.

[Zeik75]

just drive it till it dies I say, Mine has lasted a year now with similar problems but never let me down.

[SuperHbody]

I wouldn't be so quick to blame the transmission. Switching it out of gear at high speed isn't a good idea, especially considering the finicky nature of the 440T4. I would say check the fuel filter and get the injectors looked at. If its running that rough all the way up to highway speeds it could be a bad injector.

[Drive-In]

Zeik - That's what the guy at the trans shop said... valve or spring - drive it to death, but he didn't suggest replacing the vacuum modulator (which I did and got a huge performance boost out of it) for $ 13.00 usd.

SuperH - the filter is about two years old but I've been wondering about the injectors. Do you know of a guide for diy'ers on injector testing? FYI, it also idles rough even after going through the ignition system so I've still got that to contend with and I suspect injectors could play a role there too.

Thanks for your input guys.

Mike

[crash93ssei]

Years ago I had an old 1989 SE, my first Bonneville and what made me love these cars. Anyway, that car always had a rough ride / vibration at highway speed as well. After going through all the ignition system, I had just about given up when I drove it to my uncle's house, who was a master mechanic. He broke out a set of noid lights which are used to test the injector pulse from the PCM. Sure enough one of the injectors was not getting a pulse to fire. Replaced the PCM and all was good from then on.

He also showed me a little trick to do this same test at home. Take a regular 194 12 volt bulb, this is the push in style bulb with the connection tabs bent up around the glass base. Bend those connection tabs out so they stick out from the bulb. Start the car up and drive it around if you have to to make it get the rough idle / rough drive at speed. Pull back in your driveway and park it but leave the engine running. Pop the hood and unplug an injector then insert the tabs from the bulb into the injector harness, it should flash with the pulse from the PCM. Do this to each one, one at a time, all six should flash the bulb, if one or more doesn't I would replace the PCM.

[Drive-In]

Thanks crash - I will go do that. I'm concerned about unplugging injectors, having never done it before and I hear they can be expensive to replace. Any "bewares" I should be ware of?

Mike

[J Wikoff]

Just push the metal u-clip towards the injector with your finger and pull the connector off. Very easy.

[Drive-In]

Thanks J Wikoff, I saw the clips don't slide back so that helps. I warmed the car up, put a screwdriver against each injector and using a stethoscope, listened for service and all six sound like they're working. I did think I noticed a little bit of variation in what sounded like strength. Do injectors work/not work? Or can they begin to function poorly?

Should I use the lights anyway?

Thanks again everyone.

Mike

[SuperHbody]

Using the lights as Wikoff suggested would still be a good idea. It'll tell you how strong the pulse is. You'll know when an injector gives completely, it'll do a crazy misfire. The only other item I could think of causing such roughness under load could be a slowly clogging catalytic convertor but that usually causes the engine to fall on its face as the rpm's climb. My 1988 LE has a rough idle when in gear that causes some vibration into the cabin but I have no issues with it driving. Haha, wish I could be of more assistance, I just started school to be an auto tech.