I have an 88 DIS 2.5l. It idles fine and runs great at 25% or less throttle, but immediately starts backfiring and bucking when you give it any more gas than that. If I keep a light foot and keep the RPM's between 2k and 3k (I have a 5spd) it is perfectly drivable. It will backfire even at idle if you give it much gas. The problem gets worse in higher gears, probably because more throttle is required. You can't even tell there is a problem unless you try to give it more than a little bit of gas. It cruises at 65mph without a problem and runs smooth as can be other than when under load.

If you give it a lot of gas, sometimes it will pick up and have normal power, but only for a second or so before chugging and backfiring again.

The problem first manifested last night after I had been cruising for a long time on the highway. It came out of nowhere and has not gone away since. The engine throws no codes, and my Check Engine light does work and has flashed codes before (Bad wire to MAT sensor 4 days ago, fixed). The engine has run flawlessly before that other than the very occasional miss under heavy acceleration. I should note that I have an original catalytic converter, and it does not look good. I suspect it may be the problem at this point but wanted some other opinions. I have already replaced the plugs and wires.

Any ideas?

The cat very well may be the problem, but I would look at the coil packs and ignition module too.

Definitely sounds like a cat problem. If it's the original i would punch it. Here in NY it's not necessary to pass inspection anymore.

So try pulling out the O2 sensor and see if the power returns. If so yes you have an exhaust restriction (bad cat most likely). If removing the O2 sensor doesn't make a difference check your fuel pressure - and be checking it when the trouble happens and see what happens with it.

I'm getting the cat removed anyway. In Indiana there are no inspections of any kind, period, so I'm not worried about it.

Someone told me that old catalytic converters were somewhat valuable as scrap...anybody know anything about that? Don't want to sell it to some shady junkyard for less than it's worth.

quote Originally posted by MadDanceSkillz: I'm getting the cat removed anyway. In Indiana there are no inspections of any kind, period, so I'm not worried about it. Someone told me that old catalytic converters were somewhat valuable as scrap...anybody know anything about that? Don't want to sell it to some shady junkyard for less than it's worth.

Yup, they are worth money. Sorry about the engine trouble David! It made it flawlessly the whole way up there to Indiana.

I know a guy here to picks up used cars, cuts the cat out, and then scraps the car. Not sure who you sell them to, but he seems to be making pretty good money doing it.

Yes you can. Some places will pay up to $10 a lb. for cats. Call your local recyclers and see.

I had a similar problem with my SC 3800 once. If I gave it too much gas it would miss and skip to the point where I would actually slow down Turned out to be a bad ign module (the unit under the coil packs).

I had an '87 Duke with DIS. Anything more than half throttle would cause bucking and chugging. It turned out to be a clogged fuel filter.

Another time it only did the bucking at a certain throttle position. That was a bad TPS. If you gave it full throttle it would run fine.

My one and only clogged cat acted as if the car had no power. It would not buck or miss though. Idled perfect.

EGR function OK?

Check MAT. MAT can be damage by backfire.
Check plug and plug wires next. DIS hates Bosch Platinum and some "improved/performance" plug.

unplug and cap vacuum to ECM.

See my cave. Emission and DIS under engine section.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

quote Originally posted by theogre: Check MAT. MAT can be damage by backfire. Check plug and plug wires next. DIS hates Bosch Platinum and some "improved/performance" plug. unplug and cap vacuum to ECM. See my cave. Emission and DIS under engine section.

You mean EGR? I'll check out the EGR. No MAT codes. Almost all the sensors were replaced by the PO.

I guess I'll change the fuel filter next. The plugs and wires were plain old AC Delco, the only thing I put in stock Fieros.

Stupid question, where is the fuel pressure testing port on an 88 2.5l? It will do this even at idle if you smash the gas so if it is a fuel issue I could very easily find out by having someone hit the gas while I watch the PSI gauge.

Also, how is the 88 ECM as far as actually setting a code if a sensor is bad? From what I'm hearing, you're lucky if it even sets a code for a bad sensor...

quote Originally posted by MadDanceSkillz: You mean EGR? I'll check out the EGR. No MAT codes. Almost all the sensors were replaced by the PO. I guess I'll change the fuel filter next. The plugs and wires were plain old AC Delco, the only thing I put in stock Fieros. Stupid question, where is the fuel pressure testing port on an 88 2.5l? It will do this even at idle if you smash the gas so if it is a fuel issue I could very easily find out by having someone hit the gas while I watch the PSI gauge. Also, how is the 88 ECM as far as actually setting a code if a sensor is bad? From what I'm hearing, you're lucky if it even sets a code for a bad sensor...

No fuel pressure port... you have to put something inline, I just tested mine by putting a gauge on the pressure side and ran the pump.

quote Originally posted by jaskispyder: No fuel pressure port... you have to put something inline, I just tested mine by putting a gauge on the pressure side and ran the pump.

I'm sure that saved GM about 45 cents per car, totally worth it to skip adding a fuel pressure check valve. Off to change the fuel filter now...

Crank sensor? When mine went bad it would backfire.

Fuel pressure... cave, TBI adapter in 4 cyl engine section

Ooppp Yes, I ment EGR...

MAT code mean nothing most time. Check MAT, pull MAT out a look. Look Burnt? replace it after you fix backfire problem.

Setting code mean totally dead sensor and sometime bad sensor would set "wrong" code...

Example MAT... Bad sensor usually set DTC 45 at idle and not DTC 25 bad MAT. Why? Bad sensor lies to the ECM... (cave, DIS article)

EGR or DIS can cause backfire...
Discon vacuum to EGR should help to eliminate EGR.

DIS... Read DIS article in cave... Bad coil(s), plug, or plug wire, is a good bet. PIM work or totally dead, not much gray area... Try testing PIM at auto part store before you buy a new one. Accell coil? Replace them. Accell coil = crappy product.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

quote Originally posted by MadDanceSkillz: You mean EGR? I'll check out the EGR. No MAT codes. Almost all the sensors were replaced by the PO. I guess I'll change the fuel filter next. The plugs and wires were plain old AC Delco, the only thing I put in stock Fieros. Stupid question, where is the fuel pressure testing port on an 88 2.5l? It will do this even at idle if you smash the gas so if it is a fuel issue I could very easily find out by having someone hit the gas while I watch the PSI gauge. Also, how is the 88 ECM as far as actually setting a code if a sensor is bad? From what I'm hearing, you're lucky if it even sets a code for a bad sensor...

Until I replaced the mat, map, o2, cts, iac each one of them would throw a code the second I started the car, or within 15 minutes. Especially the damn MAT sensor. The ecm will definitely throw the codes.

Never replaced the egr, but I did take it off and clean it.

The plugs are less than 3 months old btw david

[This message has been edited by jasonfox (edited 04-20-2011).]

Oh just Cherry Bomb Glasspack it already. Trust me that 4 banger sounds pretty good. Ditch the muffler and just weld in a pipe. Take the cat out and put in the 42 in. glasspack. I did that to my first 4 cyl fiero and it was great. Perfectly street driveable under low RPM and when I wanted to let loose I had the noise to back it up.
Currently designing a new type of custom headers for my v6 I'm swapping. Should rev quite smoothly when I'm finished. Like a lambo

quote Originally posted by 86_Fiero: Oh just Cherry Bomb Glasspack it already. Trust me that 4 banger sounds pretty good. Ditch the muffler and just weld in a pipe. Take the cat out and put in the 42 in. glasspack. I did that to my first 4 cyl fiero and it was great. Perfectly street driveable under low RPM and when I wanted to let loose I had the noise to back it up. Currently designing a new type of custom headers for my v6 I'm swapping. Should rev quite smoothly when I'm finished. Like a lambo

Hahaha.....no. I don't believe in cars under 200hp having loud exhausts. Usually absolutely no reason to at that point...my 300+hp 3800SC swap is as quiet as a stock 2.8l exhaust and it is still not restrictive.

That, and I hate how 4cyl's sound. I am having the muffler replaced with a quieter one and eliminating the cat altogether next time I'm in Muncie and have access to my exhaust guy. Luckily, he owes me some money because I wouldn't have the money to get it fixed otherwise...good thing I have a Fiero mechanic and an exhaust guy that owe me money right now, I can get the exhaust fixed and drink a beer while watching someone else tighten my steering column bolts

Also should mention, I took the car out for a drive today and the problem was a lot better, and got slowly worse again. I always let it warm up for 5 minutes, so after 5 minute idle I go driving down the road, and to my amazement, it did fine at anything but WOT. I wound it up to 4k a few times and it pulled just as hard as it should. After I had been driving about 15 minutes, it started to come back more. Then I got locked up in a traffic jam for 20 minutes on the highway, and had to let it idle the whole time because my starter solenoid went bad (Hope someone from Frazee sees this). After I got moving again the problem was almost as bad as before, but still not quite as bad as it had been. The car is still perfectly drivable, just a little tricky going uphill and you have to keep it in the powerband at low throttle.

quote Originally posted by solotwo: Crank sensor? When mine went bad it would backfire.

Where is that at?

[This message has been edited by MadDanceSkillz (edited 04-21-2011).]

Crimeny David, that was a new starter from rockauto. You are not a lucky man this month.

quote Originally posted by jasonfox: Crimeny David, that was a new starter from rockauto. You are not a lucky man this month.

I'm never lucky. Ever. Ever.

quote Originally posted by MadDanceSkillz: I'm never lucky. Ever. Ever.

I wish I had kept the receipt, but that was thrown away a long time ago. Sheesh. Well, at least we were able to work out a good deal for both of us. Sorry about the luck!

I had bad coil packs on my '88 duke do the exact same thing. Swapped them for new ones and it was a whole new car again.

The Crank Position Sensor is under the coil packs/ignition module. It is bolted to the metal frame on the opposite side of the ignition module. You unbolt the coil packs/IM and pull straight out as the CPS sticks through a hole in the block.

The CPS is plastic with a magnet on the end and can crack and warp with age. A new one is pretty cheap.

It's also a great time to have the IM tested and do an ohm check on the coils.

Replaced the whole ICM assembly with a spare, solved the problem.

[This message has been edited by MadDanceSkillz (edited 04-27-2011).]