Last fall, I started having occasional power loss problems ('86 SE, stock 2.8, auto) which, with some research here, sounds a lot like a clogged cat problem.

Symptoms --
Occasional "jerking" at steady cruise, couple with instances of:
(The following come in a group)
-Sudden loss of power
-Engine doesn't want to respond to throttle (even full), instead crawls up through the gears
-Will make it to highway speed, but slowly
-Deepening of engine sound
-Dropping to neutral has no effect
-Tach needle jumps around
-No Codes

At the time, I was fighting other demons, such as a bad TPS and an A/C compressor that was blowing oil and seizing up intermittently. Process of elimination -- A/C compressor's been replaced, TPS is new, etc. These problems were causing jerking at cruise and idling problems, as well, but are gone, for now.

The list of symptoms above has occurred three times in the last four days, always without warning. Lasts for as little as thirty seconds, and as much (today) as about twenty minutes, as I was trying to limp home. Then, all the sudden, I'm back to "normal," although I think even that is off from "standard," as the engine still sounds a bit strained and the gas mileage has sucked of late.

The clogged cat threads I've found have described similar symptoms, but not as intermittent problems. So can clogged cat symptoms come and go, or should I be looking elsewhere?

(Can't say how much I'd love for this to be a clogged cat -- at least that way it would be identified and can be fixed.)

Thanks for any help.

I believe that clogged cats can be intermittent.

If a large chunk of ceramic material inside the cat breaks off, it can clog up.

However, that piece can move around inside and unclog also.

One good test is to get at the cat and hit it with your fist and see if it rattles.

If it does that, then it is definately bad, if it doesn't rattle then its a maybe.

Hard to tell at that point without removing it to see if the car then runs fine.

The jumping tach tells me you have an ignition problem. How much does the tach jump around? Do you think the engine RPM is really changing as much as the jumping tach shows?

The cat is way overplayed.

If your tach is funky, then you either have a wiring issue or a bad ICM or PUC

quote Originally posted by TK: The jumping tach tells me you have an ignition problem. How much does the tach jump around? Do you think the engine RPM is really changing as much as the jumping tach shows?

Call it +/- 500 to 750 rpm around what the actual rpm is (it bounces pretty radically, so it's hard to get a good read, especially as I'm usually more concerned about traffic in front of me. ) It is not 2 or 3 K rpm, it just goes erratic in the general zone of where it should be. And no, I don't think the true rpm is varying that much; I'd feel it, and hear it, if it were. But other threads didn't mention this factor (whether by omission, lack of notice, or non-existence, I don't know), and this is one of these "any piece of information may be helpful" situations. I admit I haven't spent enough time researching to know whether a clogged exhaust can cause this effect on the tach sensor.

Before the problem occurs, and once the problem "goes away," the tach is rock solid and does not jump, and correlates with the ALDL data. So it looks like the ECM "sees" what I feel and hear. I think that the tach jumping is an artifact caused by another problem. But it's there, and a lot of you know more than I do about these systems, so I'm not about to assume that what I think is an artifact is not the real problem.

Haven't been under the car to bang on the cat yet, so I don't know about rattles. I do know that the problem's intermittent (oh, joy!)

Thanks, again.

YES !!!!!!!!!!!!!!!!!!

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Well, at this point it looks less like the cat. Had it checked, the temp range is as expected and they said there were no rattles from within. This was, however, not in the "problem" state, so it's not conclusive.

Much as I'd like it to be something simple, I'm inclined to believe that 86GT3.4DOHC is correct -- probably an intermittent wiring fault, as the ICM and PUC are both relatively new (although we all know how quickly some "new" components can die). This one's going to take some work, but it must be found, because the car's running too well otherwise.

Clogged cats can always deposit thier remnants in the muffler, anyways though a clogged cat will backpressure and cause a huge temp spike and within a minute or two your engine temp will be maxxed.

The test for a clogged cat is to remove the 02 sensor this lets the exhaust out thru the Y pipe
check for code
before you check for code tighten ground wire also clean & tighten small ground wire that goes from battery to inner fender close top battery box
This is symtom of lose wire that leads to destruction of electrical parts.. check coil first check for corrosion and tightness of plug ins then check distributor connections
Ecm failures are most likely caused by bad wiring the wiring also over heats with time and falls apart inside sheath

[This message has been edited by uhlanstan (edited 07-08-2008).]

I had the exact same issues with my SE, turned out to be a bad coil.

Thanks, Jake (and to everyone else who responded). Looks like it may well have been the coil. Replaced that and test drove it, so far, so good. (I'll say that, then tomorrow the problem will come back). Engine sounds better, at least. Still getting what seems to be a slight jerk in speed every once in a while at cruise, but nothing compared to what I've had to deal with lately.

Does it ever do this when you first start the car? Coils tend to flake when they get hot, then run fine once the cool off again. I wouldnt have thought that it would effect the tach, but it is directly connected to the ICM. At anyrate, im crossing my fingers for you.

quote Originally posted by 86GT3.4DOHC: Does it ever do this when you first start the car? Coils tend to flake when they get hot, then run fine once the cool off again. I wouldnt have thought that it would effect the tach, but it is directly connected to the ICM.

Originally, it would only happen with a warm engine. As the problem worsened, I'd occasionally get a drop out for a few seconds with the engine relatively cold (at this time of year, in Texas, the engine warms up fast, so a "cold" engine is a relative term). But even then, the real trouble wouldn't start until the engine was full warm.

I'm still not 100% sure, based on the one test drive, that it was the coil. The trouble with intermittent problems is their intermittancy. (Not sure if that's a word, but what the heck.) If I make it though the next two weeks and the problem doesn't re-appear, I'll be pretty much convinced.

quote At anyrate, im crossing my fingers for you.

THANKS!

sort of a related story, think I've told it before; I used to drive a Chevette to Williamsburg and back each day - a hair over 50 miles a day. after a long diet of cheap gas, it was bogging down, I thought. Replaced plugs, wires, filters, vacuum hose and gas filter, no real change. Ran a little better for a short time, then crappy. I bought this stuff called 'Guaranteed to Pass' that was on sale, and ran through a tank of gas with that. seemed a little better for a while, then the car started behai\veing badly - I'd get about a mile from my house to a certain stoplight, then as I'd start from the light, it would bog down to almost stall.... pissed, I'd stomp the gas, and there'd be this explosion and a substantial cloud of black smoke. Then the car would run like a scalded cat all the way to work. This happened for a little more than a week, and I figured I'd be looking for a nother beater car. All I can figure is that the cleaner caused a lot of crud to leave the engine and lodge in the cat, It would load up with unburnt fuel and some backpressure, and when it got hot enough ignite! Later I crawled under the car and could see where seams had blown out of th exhaust system after the cat. Ran fine up to the day I sold that little car.

quote Originally posted by Shyster: If I make it though the next two weeks and the problem doesn't re-appear. . .

Yeah, so much for that. Was in the truck earlier today, had to run by the house & go back to the office, so I grabbed the Fiero. Made it less than two miles. Same symptoms. Didn't do this at all last night, on a longer drive. Today, you could tell from the start that she didn't want to go. Lots of "bumps" from the start. Went back home, got the truck.

One more bit of information that may be related -- I had a shop do the a/c compressor replacement, and the day it was done they called me and told me there was a broken vacuum hose they couldn't get to without pulling the upper plenum. Since it was there, I went on and had them do it (mistake #1, I know). Got the car back, and within ten minutes the SES light came on and stayed on. Code 32, EGR. Knowing that vacuum lines had been disconnected and maybe not reconnected when the plenum was moved, I took it back to them, and they assured me all the lines were hooked up. After a frustrating week of hunting for the problem in limited spare time, I found two ported vacuum lines disconnected at the base of the throttle body. DUH! Guess where the EGR solenoid vacuum port is? Reconnected those lines, Code 32 goes away.

Now, I was distracted because the stupid SES light would come on after a few minutes of driving and stay on (when 32 sets, the SES light won't go off until the EGR solenoid vacuum switch changes state), so I wasn't being totally attentive to other symptoms. But I don't recall the current problem occurring during the Code 32 interlude, although it had before. So just for the heck of it, the next chance I have I'm going to disconnect (& plug) the EGR vacuum line and drive it just to see what happens.

Edited -- kept typing '33' for some reason, meant '32'

[This message has been edited by Shyster (edited 07-15-2008).]

Then, again, this problem may have already been solved, at least in two other forms.

https://www.fiero.nl/forum/Forum2/HTML/082965.html
https://www.fiero.nl/forum/F...2/HTML/045528-4.html

I've already run continuity checks on the EGR solenoid connector, but the problem has been intermittent. If this turns out to be an intermittent ground fault in the EGR solenoid wiring harness, I promise to personally PM Buddycraigg and instruct him to tell his wife to kiss him. Profusely.

Further bulletins as events warrant.

An update --

After finding threads in which Buddycraigg and DAVES85GT mentioned (steady) symptoms strangely familiar to my intermittent ones, I started digging around the EGR solenoid connections, as the wire that powers the high side of the EGR solenoid coil also supplies one bank (from Buddy's description, the 1-3-5 bank) of injectors. Disconnected the EGR solenoid coupling and looked for any continuity glitches while moving the cable around. Nothing there, at least that I've found. For example, pin D in the coupler is connected to ground, ohmmeter from D to ground shows zero, and stays that way while being moved. So there were no obvious wiring faults that are being caused by vibration.

However, static resistance from pin A to ground is about 20 ohms (+/- 1). This seemed odd, as A is the 12V supply, but not impossible, as there are solid state circuits (like the ECM) tied into the same circuit. If anyone is sufficiently curious to check this, I'd be interested in knowing what it is on another car. (This is pin A on the plug, not the EGR solenoid socket.)

So curiosity gets the better of me, I use Buddy's trick of jumpering pins C-D together to avoid the dreaded '32', tie the plug off to a safe location, and depart for a short test drive with the EGR solenoid out of circuit. Smooth as glass. Smooth as in, the car has not run this cleanly in quite a while. Had the computer on the ALDL port, and finally the BLM is not stepping up to 150 and staying there. Pulled in, shut WinALDL down, disconnected the plug to take the ECM out of ALDL mode, and the idle went to where it is supposed to be and stayed there, which it hasn't been doing. So maybe, maybe, I've got the problem isolated. The only explanation I have for this is that the EGR solenoid coil is intermittently shorting, at least partially, and pulling the voltage supply line down below the minimum operational voltage of the injector relays. (But not pulling enough current to fry the TBI INJ 2 fuse. (Schematics are reproduced in Buddy's threads referenced above, see 8A-21-1 and 8A-21-3). May have to disembowel the EGR solenoid to find out.

I'm going to try driving it to work tomorrow, with the computer connected to see how things look.

well i have no eFFin idea.

i would have been pointing at the ignition parts in this order.
tach filter
ignition module
pickup coil
bad connectors on any of the above items.

Well, once again I have succeeded in developing information about what the problem isn't. Car ran well for the most part all day, drove it around a bit at lunch. Had a few "bumps" at cruise, and once or twice idle dropped at stoplights to about 500, but picked back up. All of this could be attributable to having the EGR disconnected, though somehow I doubted it. Got a good ALDL data file driving into the office.

Driving home, got in a bit of stop-n-go traffic, and the car almost went into the problem mode, but caught again. Then, about a mile and a half from home, she does it. Had the laptop with me but not running, so I pulled to the side of the road & hooked it up. Drove a couple of miles through a subdivision that has a big oval street, so I've now got about five minutes of ALDL data with the car in failure mode. The problem also "cleared" (mostly) as I was about a mile from the house, so part of the file has that transition. Can't say I can see anything that tells me what the problem is. Certain sensors seem off -- the IAC and MAP among them, but these oddities may be caused by the problem rather than indicating anything about its cause. Anyone bored enough to take a look, PM me your email address and I'll email you the ALDL file (about 100K).

I guess the next step is what Buddy and 86GT3.4DOHC suggested, down the ignition control side.

[This message has been edited by Shyster (edited 07-18-2008).]