I've got an 87 2.5 and 2 days ago whenever I step into the throttle any amount it stutters and backfires thru the exhaust. It idles fine and runs fine so long as you don't try to push it any. Just today I put new plugs in it (OEM AC's) with no change. Any ideas anybody?

Check all around your distributer, make sure all connections are good. I had that problem and it was a loose connection.

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Mark Matthews
'87 GT Fastback T-top

87 doesn't have a distributor, but do double check the wires on the ignition...

Also check both MAP and MAT. Read DIS notes in my cave. Choking when you punch it is often a sign of a MAP with a vac line problem or even a bad MAP sensor.

Check the whole thing for vac leaks while your're at it. Don't forget to check at the brake booster... Clamp all the PCV valve joints even if they seem ok. (Be gentle or you'll ruin the rubber elbows.)

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11-Sept-01, The day the world as we knew it ended.

I found a broken vac line to the carbon cannister control unit and repaired it. Also checked for codes and got a 51 - Prom failure. Reset and ran it several days -- no problems. Last nite after sitting in it idling for quite a while(waiting for daughter) it got quite warm (not overheating hot but very warm for winter) and on my way home it was backfiring thru the exhaust , stumbling and stalling.
I checked for codes and it had a 51 again and a 25 -- Mat sensor. Now after the car cooled down it runs fine. I pulled the mat sensor off and checked it at work. At 65C (150F) it shows 863 ohms and at 20C (70F) it reads 5009 ohms. It has carbon all over it and I was wondering if these readings being substantially over what I have read in theogre's info would cause this problem. -- Thanks for all the help.

Glad you found the leak.

Acording to ALLdata,,, Temp sensors MAT/ACT and Engine Coolant should test as follows.

Ohms @ Deg F/C
7500 @ 40/4
3400 @ 70/20
1800 @ 100/38
450 @ 160/70
185 @ 210/100

The main problem is that 51.... that's likely the ECM bad. The connections between the PROM socket and board have probably cracked. If they have then other stuff may have also.... You can get used ECM's easy enough or just spring for a rebuilt. 87-88 Grand Am and 87-91 Olds Cutlass Calias. under the passengers side of the dash.

The MAT sensor, when it starts screwing up usually does it at Idle first.

The fact you've had it backfire, likely thru both intake and exhaust, means the MAT should probably be replaced at the same time as the ECM.

After replaceing stuff... Don't forget to recheck vac lines to make sure a backfire didn't loosen one or blow it off.

Sprung for a rebuilt ecm today ( from Pontiac) and now things have gone from bad to worse. The check engine lite is on all the time (cannot even check for codes) and it feels rough at idle. It seems that I've traded an occasional problem for a constant one. Anyone got any ideas? -- Thanks

Check O2 Sensor.. My car acted same way...O2 replaced... and new injector fixed the problem for me.

Why is the 87 2.5 so finicky?

I had (and still have) backfire/stumbling when I gun the accelerator.

I've replaced the MAT, MAP, and coil packs.

Since replacing the coil packs, the car runs A LOT stronger, but still when I gun it, the car buckles/backfires.

I'm going to replace the MAP sensor holder thingy with one I've gotten off a used Fiero... Perhaps that will help...

I'm at a loss on this one... Car runs great except for when I gun it.

KV

Add my name to the list of weary 1987 2.5 owners. I've fixed so many things on my engine that there isn't much left that hasn't been repaired or replaced!

I also had a hesitation/backfire problem under hard acceleration. Replacing the coil packs, spark plugs, and plug wires fixed my problem. I still have that "time bomb" problem, though. I just put a new fuel pump in it today. Tomorrow I'll know if I finally have it whipped.

I wish I actually had some useful advice to give, but I'm too tired to think straight. I'll give you some moral support, though.

[EDIT] I'd take that rebuilt ECM back to Pontiac and have them exchange it. Sounds like it's probably fried. Either that or they accidentally gave you the wrong one.[/EDIT]

[This message has been edited by Blacktree (edited 01-24-2002).]

[This message has been edited by Blacktree (edited 01-24-2002).]

[This message has been edited by Blacktree (edited 01-24-2002).]

I took the afternoon off work as it was sunny and relatively warm (for here) to sort out my car -- no garage to work in. After resetting the computer and rechecking everything -- to no avail I went back to the Pontiac dealer to ***** and after checking it turns out the ecm they sold me had no prom in it!!!!! Luckily my old ecm was still on their shelves so they switched it and it's in the car now and so far everything seems to be fine. Hopefully this will take care of it. Thanks to everyone for your help and ideas.

Had the same problem, did the same T/S procedures as described here as well as in Ogre's cave... Thought I'd solved it with some new coil packs, it ran better afterwords but still would go stupid occasionally.
I kept digging at it and eventually found a cracked/misaligned crankshaft position sensor.
It has run great for the last year but I think mine was an isolated problem. I did find that these engines are very sensitive to coil packs. Don't assume new ones are adequate.
Ogre knows more about DIS than anybody, follow his suggestions and you'll be fine.

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Bob Cardone
Suncoast Fieros

'85 2M6 SE Targa

I don't know what more I can tell you. Here's the stuff I can think of, even the grasping at straws items.

Presently I'm working on updating the DIS article. (God... not more time on DIS... Please not more time one DIS... It's a great system but I've already learned more about it than I ever wanted to know.)

With waste spark DIS I have a rule I generally follow.... It's not in the cave because it's partly a judgement call and I don't want everyone just trashing parts at random.

The rule is that anytime a coil is replaced, you should, more often than not, replace the plug wires and plugs at the same time. (I still stand by the use of Borg Warner's wires and standard AC or Autolite spark plugs.)

If a wire or plug is bad it can take out the coils. Especially in this DIS motor because of coil placement. Bad wires or plugs make increase load on the coils and that means more heat.

The Iron Duke runs the ignition on the side of the block. Thermally it is really pushing the limits. In most other engines using DIS, the whole mess is on a bracket sitting over a valve cover, a Much cooler location.

Also Fiero engine bay, as we know, is hot. Often hotter than the same drivetrain in a FWD car... This doesn't help.

Now that said... I'm going to check my EGR tomorow.... It will be a few days before I see if there are any results so don't ask tomorow.

Frankly, I've had the POP on Stomp problem myself on occasion lately. I've got one of those damn universal EGRs on it. I'm going to put the old one back on and see if it changes any. (Everything on my motor is in very good shape.)

I'm looking at the huge line going to the brake booster as well... I have a suspision about having such a huge, long, line connected to the motor. I'm wondering if, when you stomp the pedal, that line has enough vacuum capacity to starve the engine for a split second. There's got to be at least 40-50 cubic inches of volume in that line. My idea is to install a second check valve in the line near the engine. That should keep the line from scavenging the manifold under sudden throttle open. (I don't think it will hurt the brakes any. Ultimatly it turns the long a_s line into reserve for the booster.)

Also... There is a TSB for this motor that I have mentioned before. The TSB replaces the PROM in the ECM for various reasons. I don't know if it fixes this problem you are having or not.

A copy of the TSB can be found here---> http://theogre.home.sprynet.com/tunnel6/promtsb.zip

Don't even think about ordering a PROM w/o scanning the ECM to get the ID number! The notes I put in that zip file are not fully tested. Don't count on them being accurate. The PROMs run about $60-$70 thru a dealer. I'm looking for alternate sources.

I'm not promissing the replacement PROMs will fix this problem. I don't know much about them. I'm planning to get one because of the minor knock problem listed in that TSB. I don't know when that will happen. (My engine is in really good shape but I have to run 90+ octane or it knocks. That's getting really old. This motor should be ok on 89 or even good 87.)

timing chain?Look at position of rotor with # 1 piston at top dead center .

fee-air-oh,
Dude... 87-88 4 cyl has no distributor.... DIS motor.

All,
I took of the Wells universal EGR today.

1. The thing is pretty carboned up for 2-3 years old.
2. The bolts were not very tight. Not loose but not much to undo.
3. There was a carbon trail between the exhaust and intake ports on the manifold.

EGR's on this motor are a pain to mess with. You need a very short end wrench or a crowfoot. BTW, the bolts are 10mm on mine. not 13.

Don't forget anti seize on the bolts.

I put the factory EGR back on just for kicks. (I saved the old one in case I need the number that's stamped into the shell.) The factory ones are consideably differant from the universal ones.

I'll see how it runs over the next few days and let you know.

TheOgre said:

quote The Iron Duke runs the ignition on the side of the block. Thermally it is really pushing the limits. In most other engines using DIS, the whole mess is on a bracket sitting over a valve cover, a Much cooler location.

To which I reply:

Yeah, when I replaced the coil packs and crank sensor on my car last week, the freaking ignition module was still hot to the touch after letting the engine cool with the decklid open for over an hour. I agree it's a REALLY bad location for sensitive electronics.

I think it shouldn't be too hard to modify the DIS system to relocate the coil packs and ignition module. The electronics (crank sensor, ignition module, coils) are all bolted to an aluminum plate. The aluminum plate is in turn bolted to the engine block. The crank sensor is connected (electrically) to the ignition module using a 2-pole connector.

Now, imagine this:

You remove the ignition module and coil packs from the aluminum mounting plate and attach them to another mounting plate somewhere else (in a cooler location).

You then connect the crank sensor and the ignition module using a two-wire cable, with a male-female plug, so parts can be replaced without taking a soldering iron into the engine compartment.

Thoughts? Opinions? And my apologies for the off-topic comments.

[This message has been edited by Blacktree (edited 01-27-2002).]

Actually, I thought of that already. I've even got a cut down crank sensor so that I don't have to solder to the module, which runs $120 or more to replace.

I'm not sure if it's worth the effort. I've got most everything I'd need to do it. When the system works right, it doesn't seem to care. It's not until something overloads the coils or something that the hot location matters. (Altho if the PIM shield is missing that will also cause trouble for various reasons.)

My thought was to mount the "new" setup on a bracket anchored by a bell housing bolt. That would let you get it off the block but still allow all the other factory wiring to work.

Well.... I'm still watching for problems but so far it looks like the EGR was acting up on mine.

I don't think the EGR valve was bad as much as I think it was leaking at the base.

The gasket for these is about $1. I'd recomend replacing that just to eliminate it.

If you do have to replace the EGR avoid those bloody unversal jobs with there user attached metering washers. I don't think the thing is bad but I don't think they are "right for it." Making the EGR work right on a motor is more than just setting the metering washer...

Right now I've got the factory original EGR on it and haven't heard a bit of knock or had it backfire when I punch it.

Well.... as I looked at it more today... My old Wells unit is rattling inside. I'd say it was definatly toast on top of leaking past the gasket....

day 3 and car still runs really good.

While digging in www.partsamerica.com I found this one...

AC DELCO 214-5513 $50.49
Gasket Not Incl.; OE #17084743

(87 DIS 4 cyl)

The FelPro gasket is about $1.

I don't know if that's just AC's version of the universal jobs... I hope not. It can't be any worse than this POS Wells that only lasted 2 years.

[This message has been edited by theogre (edited 01-29-2002).]

The Ogre You never did mention the spark plug gap. DIS is very sensitive about gap, Bosch Platnium in particular because the electrod wears into the porcilin and cant be seen and regapped.

The typical symptem is backfire through the carb and exhaust particularly when under hard acceleration or heavy load.

No, I didn't mention it here... I'm pretty sure it should be in my cave article.

DIS is picky about gap---> .060 inch (1.52mm)and only that. Too little and they just don't perform right. Too much and you can actually fry coils. Never assume new plugs are correct. Always check them. They can take quite a beating in shipping.

The best plug guage is the wire type. Taper ones are useless and flat feelers can be thrown off by the slight edge where the shell electrode is cut. Feelers would probably work ok on "double platinum" plugs from AC and Autolite but only then as a last resort. (Most feeler sets can't do .060 without stacking gauges. Stacked feelers are nearly always a little thicker than a single of the same thickness.)

We've covered those bloody Bosch plugs I don't know how many times now. Those go back to pretty early in the forums existance I think... Never ever use Bosh Platinum or Platinum +4 in waste spark DIS.

As for my car.... It's still doing good after the EGR fix. (I didn't touch anything but the EGR...) I think the fuel mileage is back up as well. I'm out 100 miles now and am still over 1/2 tank. I'll track that over the next few tanks to be sure. (I think that Wells EGR was bad a long time ago. What a POS.)