I have a 1988 Fiero GT 2.8 V6 with Automatic Transmission. While driving down the highway the car began momentarily loosing power intermittently for durations of about 3 seconds. Pushing the accelerator pedal appeared to help clear the problem, but over time the frequency of the problem gradually increased until the INJ 1 FUSE blew. I spent time looking for short circuits between the fusebox and the ECM. I haven't found any, nor have I found continuity between the INJ 1 circuit and the INJ 2 circuits downstream of the fusebox. The frequency of the problem increased until the fuse would blow when ever I started the car and applied any pressure on the accelerator pedal. I ended up replacing the ECM. The acute problem went away, but when I drove the car on the freeway for about 20 minutes, the INJ 1 FUSE blew again. Immediate replacement of the fuse didn't help. Hence, I think I damaged the replacement ECM. (I had to have the vehicle towed home.) I had read in the service manual that the electric resistance between many ECM pins should not be measured with an ohm meter. (At one point when I purchased the car I had measured resistances between various pins while trying to troubleshoot another problem, but I thought was only probing between pins that were not forbidden.I had probled the second EMC had also.) Therefore, there is a possiblity that replacing the EMC yet again, but with an presumably untampered ECM, might solve the problem. I went and checked the various ground connectons from 501 to 505. I didn't notice anything unusual. Before, I replace the ECM again, does anyone have any advisement for troubleshooting steps I can take? Is there something I am overlooking?

Im betting neither of your ECM's are blown. Look at the INJ1 fuses job, It goes from key on power to the fuse, then straight to 3 injectors (2,4,6), supplying them directly with power. From there, the injector is wired to the computer. The computer grounds the wire to complete the circuit to fire the injector. You need to pull the plenum and check your wiring, as well as the injectors themselves. If an injector's winding breaks down and shorts to the case you'll see that immediately with a meter. You should have I think around 10-14 ohms across the two contacts, and infinite resistance from either contact to ground. As far as the wiring is concerned, Most likely the pink/white wire (which goes directly to the INJ 1 Fuse is shorting out somewhere. It goes from the fuse box to the C203 (white and black connector directly below the ECM in the center console (position J)) then it goes to a 6 wire connector under the intake plenum near the thermostat (position A) to the injector harness, where it splits up and goes to the 2,4,6 injectors. Odd's are you have a short somewhere along that wire or at an injector itself. Since the ECM only grounds the wire at the other end of the injector, having a shorted (to ground) wire isn't going to damage the computer, but it will blow the INJ 1 fuse.



Oh, and Welcome to the Forum!

[This message has been edited by Fierobsessed (edited 10-11-2011).]

According to the prints, 135 injectors are in parallel as are 246. This would indicate that all three from either fuse fire at the same time? If this is the case, and one of the injector coils in the inj 1 fuse circuit is shorted internally, it would be the path of least resistance preventing the other 2 in it's parallel circuit from functioning. (loss of power). It could cause the eventual failure of the fuse as it would be a momentary short to ground when it fires through the computers circuit to ground. Broken or shorted coil windings can cause weird problems. They can meter fine when cold and change value when warm etc. I would suspect a problem with an injector (2,4 or 6) in the inj 1 fuse circuit. I have had shorts in the factory plug connections also, so don't count them out and check all closely.
With plugs disconnected, I would measure resistance from A to B and compare it to the resistance from D to C (using above prints). If 2,4 or 6 is shorted, there should be no resistance or almost none. Comparing to the resistance from D to C should give you an idea if there is a problem. Not sure what the values should be they should be similar. Keep in mind that coil problems are odd and don't always present themselves when metered.
Another thing to try would be to swap injectors 246 with 135. If one of the 246 injectors is shorted internally, the problem should transfer to the inj 2 fuse.
Or just replace 246 with injectors from a salvage yard and see if it goes away...just not a solution that provides peace of mind.

Best of Luck!

+1 on checking the resistance of the injectors or just replacing them.

Thanks for welcoming me to the forum. I did previously disconnect the 6-way connector and then indivually check for continuity between terminals A through D and the negative terminal of the battery. Ididn't find any shorts. But I didn't even consider what could be happening at the injector itself! I was at my wits end. You all have given me great advice. Thanks very much. I'll let you know how it goes.

I just checked the resistance and got

A-B 5.6 Ω

C-D 5.5 Ω

That is all three injectors at once

Testing one single injector I got 16.1 Ω. I only checked one.

I agree with all above. My guess is as one of the inj.s is shorting internally either in the coil or to ground once it gets heated up. That is why it happens after your driving a while. Once cooled your not seeing the short. You could try measuring across the inj.s and then tap on each inj, and also check from the coil to ground. You might find one that way that has a problem. Your ecms should be good since to blow the fuse the short would have to happen at or before the inj.s. Since the ecm grounds the inj.s a short somewhere would have no affect on the ecm... Only possible way to blow the ecm would to apply +12 directly to the ecm output with no resistance load when it tries to fire the inj.s.

[This message has been edited by Dodgerunner (edited 10-12-2011).]

quote Originally posted by phonedawgz: I just checked the resistance and got A-B 5.6 Ω C-D 5.5 Ω That is all three injectors at once Testing one single injector I got 16.1 Ω. I only checked one.

Sounds reasonable to me without running calculations. If on the engine in question the resistance from A-B was 1.3 or 0.8 ohms or something like that, I would expect an injector coil to be shorted internally.

All this really means is that instead of the electricity travelling from one terminal on the injector all the way through the hundreds of wraps around the core and back up to the other terminal of the injector plug, the electricity would be travelling in one terminal and jump from one winding to another through a break in the insulation bypassing most of the internal coils and out the other teminal. This results in less resistance as there is less wire distance traveled from one terminal to another.

I only had time to measure the resistance between A-B and C-D. They were identical: 5.4 ohms. This confirms the suspician that the short only occurs at high temperature. Thanks for the suggestion to tap the injector when taking a resistance measurement after I pull the plenum off. I was wondering how I could identify the presumably bad injector without putting it in an oven. Most likely I won't have time to pull the plenum until friday night. BTW... new injectors are pricey. I am hoping to fully verify a damaged injector is the root cause. Now I'm anxious to start working on it. Do I really need to disconnect the coolant lines runnning over to the throttle body, or will there be enough slack in the lines to just lift the plenum upward to get some probes to the injectors or tools to remove each one?

You could ohm test both banks again with the engine hot. That should help you verify a problem before pulling the intake.

But the engine gets hot and runs for a long time before the problem manifests itself. If the cold resistance readings are good, I doubt that the one time hot resistance readings will give a black and white indication of if they are bad. I think the best thing to do would be to purchase 3 used injectors from the MALL section of this forum. Before installing them verify that they do open when you apply a 9v signal from a battery. The injector should click and you should be able to blow through it. Replace all three on the suspected bank and see what happens.

Replace the o-rings of all the injectors when you take the fuel rail out.

I think the best route at this point considering time and money, would be to swap the three fuel injectors between A-B with the three injectors b/w C-D. if the inj 2 fuse blows, it is a perfect indicator that the problem is in fact one of the three injectors in the original inj 1 fuse curcuit. If the inj 1 fuse blows again we will all know that we are barking up the wrong tree. It is quite possible that simply swapping the injectors will cause the problem to hide for a while and not resurface...but still ultimately be there. I wouldn't worry too much about the o-rings for testing purposes but would swap them all out once you are certain. Used injectors are quite cheap at picknpull.

I had this fuse blowing a few years back. In my case it turned out to be the wiring harness between the engine and the firewall had gotten come loose from a clamp holding it to the firewall and was brushing up against the hot exhaust. when it brushed against the exhaust hard enough, it blew the fuse for the fuel injectors. Its a long shot, but take a close look at your wiring harness to make sure you do not have the same issue.

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87 Formula Clone, 3800SC, 3.4 pulley, 4T65E-HD, HP Tuners, 12.98 at 103.4 1/4 mile, Regal GS Gauge Cluster.

quote Originally posted by Reallybig: I think the best route at this point considering time and money, would be to swap the three fuel injectors between A-B with the three injectors b/w C-D. if the inj 2 fuse blows, it is a perfect indicator that the problem is in fact one of the three injectors in the original inj 1 fuse curcuit. If the inj 1 fuse blows again we will all know that we are barking up the wrong tree. It is quite possible that simply swapping the injectors will cause the problem to hide for a while and not resurface...but still ultimately be there. I wouldn't worry too much about the o-rings for testing purposes but would swap them all out once you are certain. Used injectors are quite cheap at picknpull.

i agree, swap the injectors... its quick and dirty, and will get you the answers you seek wether or not you have a bad injector. this is sound advice from my Reallybig friend!

I started the process of removing the air plenum and then realized... hey, I have to remove the fuel rail! Egads... what is a good way to deal with the fuel in the rail, put a towel underneath an injector and then pull it out? Secondly, are there only two bolts holding the rail onto the plenum and do you happen to know what size socket the bolts require? It looks like a bit of work: something I don't want to have to do twice. Maybe I should just bite the bullet and replace all six at once with new ones (a big ouch on the pocketbook); presuming that I will clearly confirm that the issue is with one of the injectors. I saw that the fiero store sells a complete set. Is this a good price or should I go to O'reilly's or Autozone to purchase them? At least I could get some immediately from a local autoparts store. Any advisement on that?

It is a bit of work, but nothing worth doing is easy! Pull the fuel pump fuse and try starting the car by turning the engine over for around 8 seconds. That should remove the pressure from the fuel rail for the most part. When pulling a line off the rail, I would put a rag underneath to catch the leaking gas and wear safety glasses. Swap them out A-B / C-D and give it a try. Look at it this way; at least the work you are doing is on the top of the engine and not at the back or underneath. I'll take it any day over swapping out a clutch! Another human being put the car together, there is no reason why you shouldn't be able to pull it apart.

Don't forget to put the fuel pump fuse back in the fuse block!

Clean around the injectors to prevent dirt from entering the engine. Don't forget to lube the injector o-rings with oil before re-installation.

[This message has been edited by Reallybig (edited 10-14-2011).]

I have to 'fess up and say that I wimped out on purchasing an entirely new set of injectors. I'm not quite ready to spend the $400 yet. Therefore, I left work early today and went to pick-n-pull and found a V6 engine. First I removed the inlet plenum and discovered a bonifide wasp nest on the bottom side of the plenum! Fortunately, they had vacated the premises already. lol. Within an hour I had three fuel injectors and fuel injector harness in my hands, without breaking anything. Thanks very much for the morale boost!!! It was much more straightforward than I expected. It was also interesting to see the design of the clip used to retain the injectors in the fuel rails. I went home and promptly removed the fuel rail from my car. I noticed that the "nipple" of the number 1 injector was severely cracked and rotated, when I it shouldn't move. Therefore, I will be going back tomorrow to purchase that 4th injector and recover my three dollars worth of core charges. (Do they really expect you to drive backk to recover $1 per injector when it costs money to drive there to begin there? Is there really an ROI there? But I digress...). Hopefully, I'll have my engine reassembled in short order and test out the results. Oh... also I purchased a 9V battery and tested the injector solenoids. They all seemed to actuate properly. But again... my car's engine was having problems at temperature. Hopefully, I'll be able to post good news tomorrow.

I'm eagerly awaiting the results of your progress into the world of engine troubleshooting. Pulling parts at the self serve auto wreckers is an excellent way to learn how NOT to take things apart! Better to break a car destined for the crusher than your own car.
In years past I have made an inexpensive fuel injector tester by attaching a clear tube filled with oil based paint thinner (not really flammable) to the top of the injector and hooked up a tube from that fluid filled clear tube to a spare tire valve as a means of compressed air (35 psi). Add power to the injector terminals and evaluate the spray pattern of the paint thinner. If all is well, the thinner also acts as a lubricant to help prevent corrosion and keep the inner workings of the injector from drying out and sticking....but that's just the way I roll.
I always take the clips and screws when removing used parts from the wreckers. Differences in design might make your old clips and screws unable to work with the swapped parts. Better to be looking at the part needed than looking for it. It's also how I fill half of my parts bins with useful fasteners!
I sure hope all this work solves your problems.

After you put the new injectors in before you put the upper plenum on.

First start by disconnecting the two power leads (gray and black clips) from the ignition coil.

Cycle the key to on, let the ECM prime the fuel system by running the fuel pump for two seconds. Then inspect for fuel leaks. Do this 3 to 5 times. You need to let the key sit in the off position for at least 45 seconds to get the ECM to 'prime' the fuel pump again.

Do this prior to to installing the upper plenum.

Well... I got everything back together and the car started up OK. Fortunately, I decided to look under the hood immediately after I exited the driveway. The fuel rail area was covered with fuel. It turns out the cold start injector connection at the fuel rail is leaking. (I thought I has checked it enough before I put the plenum back on.) I then tried differen sized o-rings from the unversal set that I have, without success. The reality is that you've got to have the exact size for that fitting, especially it seems, if the car is older. I noticed the Fierostore sells an o-ring set the for the cold start injector. (I would be surpised if the GM dealer has them in stock.) It will problably take almost a week to get one from the fierostore. Based on my current work schedule I might not get to work on it again until four weeks from now. Oh the suspense...

I came across this article that suggests GM does have a replacement part. This is the url. I'm going to call tomorrow. http://www.fieropride.com/t...echArticle=Fuel_Leak
Also I came across this website that sells a cold start delete kit. http://www.tlg-store.com/product_p/fieroeng016.htm (I'll do the o-ring replacement first since it is easy and I need to know if I corrected the fuse shorting problem.)

I got back from my business trip and installed a new cold start injector o-ring. I drove the car 10 miles and then the inj 1 fuse blew again. Arghh... But I remembered this morning that I had purchased a new higher amperage (140A) alternator from the fiero store. I started having the problem after I had installed that part. I know an alternator will just deliver what you ask it for, but do you think that it may be running at just high enough of a voltage to push the injector current over the limit? I am thinking it is worth the money to purchase a stock alternator to find out, considering that I couldn't find an eletrical short in the wiring.

No

Wire leads to an amp meter - and include a fuse in your circuit and attach it to the INJ1 fuse connections (fuse removed). Now watch and see what you get for current. If the current is always high, you most likely have a bad component. If the current is reasonable with spikes you most likely have something shorting somewhere.

[This message has been edited by phonedawgz (edited 11-14-2011).]

That was brilliant advice. I went to the autopart store and purchased some fuse blades, a mini-fuse box, and wiring. I took a blown fuse and my Walman multimeter and added them in series at the main fuse panel. I drove the the car around for a while until it got hot. The ammeter reading never went above 1.5 Amps. Most of the time it was around 0.3 A. Then I stopped and let the engine heat soak. I then started up the car and gunned the engine (almost couldn't help it because I was turning into a downhill when entering the street). The fuse in the multimeter blew almost without warning, and it supports up to 10 Amps. I wonder if I heard a popping sound but not sure. After disconnecting the wiring I had added. The car started up just fine. The gages fuse was loose, and i couldn't get it to get a good connection, so I drove home with no operable gages and listening to a fast chime. So it must be some wiring short is some mysterious location with mysterious behavior; although it does seem temperature related.

btw - did you catch the fuse panel swings down? There are side releases that when squeezed (and push up slightly to let them unlatch) will let the fuse box swing down.

(ignore pen - googled pic to show unlatched fuse box)



So start the car - with the meter connected - and start wiggling wires - while someone watches the meter and lets you know when the meter spikes. Then play a game of hide and seek with the short till you find it.

[This message has been edited by phonedawgz (edited 11-16-2011).]

Here is an interesting but hopefully helpful discovery today... I rehooked up the multimeter and started up the car in order to conduct the wire wiggle experiment. Unfortunately, the multimeter's ammeter would not work. It wasn't obvious to me the fuse was blown when looking at it. I spent a bunch of time trying to find a replacement with no success (electrical stores like radio shack were already closed). Since it was dark I decided to just insert the normal fuse and wiggle wires in the dark in the hope that I might notice a spark where an electrical short may be occuring. I noticed some initial exhaust manifold smoke and sawI what I thought was too smoky of exhaust and even what I thought might be gasoline smell intially until the car started warming up. And then all that seemed to go away. I decided to let the car idle for a long time to let it fully get up to temperature. After what seemed to be 20 minutes I noticed coolant vapor leaking from the interface between the rubber hose and the metal tubing near the rear wheel on the driver side. Interestingly, this is the same location that Pep Boys noticed that I had a leak here when I orginally started having this problem and took it in to Pep Boys. I had added another clamp (in addition to the existing one) as a solution to the problem. It is clear now that does work. I need to actually replace the hose. I decided to keep letting the engine idle and just keep poking around. After about 20 minutes I started changing the throttle position by using my hand to move the linkage at the throttle body. I noticed that if I tried to hold the engine speed at exactly 1500 RPM, the engine would start faltering like it wanted to quit. This is the exact behaviour I was initially experiencing on the freeway when the problem started. Over days it got progressively worse until I started blowing the fuse all the time. Now I'm wondering if 1500 rpm happens to be the speed where the thermostat tends to open up and let coolant flow through the engine. Then maybe air bubbles in the system screw up temperature sensor readings which then induces the ECM to make gross corrections, which then could lead to too much current delivery to the injectors. It seems like a stretch, but do you think the coolant problem could really be at the root of the problem, and not an electrical short? (But at this point I know I need to fix the coolant leakage situation anyways.)

A properly running ECM could hold the inj pin low, ie keep the injector on for 100% of the time and not blow the INJ1 fuse. It can't be that the ECM is trying to fire the injector too much.

re: smoke from the exhaust manifold at start up. Sounds like you have a leaking valve cover gasket seal. It leaked some oil on the exhaust manifold while the engine was off and that oil burned up upon start up.

Here is a good thread on the ground strap
//www.fiero.nl/forum/Forum2/HTML/043240.html

[This message has been edited by phonedawgz (edited 11-19-2011).]