Real Fiero Tech

Blue Shift wrote:Hey, speaking of, I have a 91 TGP drivetrain sitting in my garage that I hope to swap when I have some time. You using the original 440T4HD?

Nop. Just the motor. Sadly I have a good ol th-125. Im looking for a muns. 4 speed to swap but for now its the fragile 125.

Alright. Im still having some trouble. Even after getting the wires straight Im still getting upper RPM backfires. After checking, Re-checking and checking the plug order again I changed the plugs. To no surprise it did nothing. So I puled the 2,4,6 wires off and tried to start it. No start. I put them back on and puled 1,3,5. What do you know. It starts, Runs as good as it did before and WtF. NO BACKFIRE!!!!!!!!! I know Im not a fucking genius but I am pretty smart when it comes to fixing things but this it the dumbest SHIT I ever came across!! I mean, It runs as good if not better then it did. so you would think it had no spark.(I did a spark test to witch all three 1,3,5 past) But when you plug them back in it backfires. OH Oh and the plugs on 1,3,5 were wet when I puled them out. 2.4.6 were dry. almost looked burnt.(Tip was clean with some white powder rez. on them.). So if any body thanks they can help please fell free to. Thanks again.

Who did the last timing belt? Is there any way the cam timing could be off?

This is the 3.1. And I dont know if the chain has ever been replaced. From what it looks like its the og. Could this be a bad ICM or maybe even a bad tune? I know there's something I looking over here..

Yah then it isn't the cam timing, as that'd affect all 6 slugs.

I don't think it could be the ICM. The coils go to 2 cylinders each, and cylinders on opposite banks, so if the ICM was bad, it'd be firing 2 cylinders off on opposite banks, so your problems wouldn't just be the 1-3-5.

I also don't think it could be the tune, for the same reason above.

Forever-Fiero wrote:Alright. Im still having some trouble. Even after getting the wires straight Im still getting upper RPM backfires. After checking, Re-checking and checking the plug order again I changed the plugs. To no surprise it did nothing. So I puled the 2,4,6 wires off and tried to start it. No start. I put them back on and puled 1,3,5. What do you know. It starts, Runs as good as it did before and WtF. NO BACKFIRE!!!!!!!!! I know Im not a fucking genius but I am pretty smart when it comes to fixing things but this it the dumbest SHIT I ever came across!! I mean, It runs as good if not better then it did. so you would think it had no spark.(I did a spark test to witch all three 1,3,5 past) But when you plug them back in it backfires. OH Oh and the plugs on 1,3,5 were wet when I puled them out. 2.4.6 were dry. almost looked burnt.(Tip was clean with some white powder rez. on them.). So if any body thanks they can help please fell free to. Thanks again.

Injector fuse or wiring? Half the injectors should be on one fuse, the other half on the other fuse.

The Dark Side of Will wrote: Injector fuse or wiring? Half the injectors should be on one fuse, the other half on the other fuse.

Depends, the 2.8l has half on one fuse, half on another, but the 3.4 has them all on a single 10A. Since his 3.1 is DIS, I'm assuming it's a swap, and the harness probably has all 6 on one, since the factory 3.1 had it like that I assume.

is the engine backfiring out the intake? or is it just popping out of the exhaust?

If its backfiring then its a timing issue as the plug is firing when the intake valve is open. Which could mean you still have the plug wires on wrong, or the ESC could be bad. Or the crank signal to the computer is bad which could be wiring or the sensor. Do you have aldl and can get logs?

Can you get video?

I still think your plug wires are on wrong. Sure it might idle ok but when you get the revs up higher the cylinder needs more spark advance and if the wires are still screwed up this will cause the problem you are seeing.

Hey this may not be the problem, but crawl your ass under and check out the wires going from the crank position sensor to your ICM. Make sure they are NOT crossed. This one dude, Dave, who set up a 3.4 DOHC chased symptoms not unlike yours for 18 months and more than one re-wire before he found that he had those wires crossed - the way the ICM saw the pulse waveform, it'd work OK at low RPM, but wouldn't have the resolution to fire them at higher RPM. Since it's a 1 minute check, you might as well.

As mentioned, did you check to make sure you're getting fuel from all 6 injectors? You cycle the key a bunch of times to push fuel through the rail? Fuses/wiring to injectors ok? Do you have compression on all 6? It can only be fuel, spark, or air/compression, so something should lead you to the problem. Go through it systematically, and shoot some video so we can see what's going on. Good luck.

I crossed the wires on my CPS, and it wouldn't run at all. No spark whatsoever.

But if the wires are just a little messed up, and crossing half the time, that could be it. Might be worth checking, but I'm sticking with Shaun. Plug wires.

Aaron wrote:

The Dark Side of Will wrote: Injector fuse or wiring? Half the injectors should be on one fuse, the other half on the other fuse.

Depends, the 2.8l has half on one fuse, half on another, but the 3.4 has them all on a single 10A. Since his 3.1 is DIS, I'm assuming it's a swap, and the harness probably has all 6 on one, since the factory 3.1 had it like that I assume.

The Fiero *chassis* splits the injector current between two fuses. If he's wired the engine into the chassis correctly, then he has half the injectors on one fuse and half on the other.

But the early 90s 60*s with DIS only had one injector fuse, so depending on which harness he used, it could be either way. I know on the DOHCs we tie the two banks together, then just leave the other circuit empty (Or use it for another purpose).

At any rate, I don't think that's his problem, but since a fuse is so easy to check, he should check it.

The CKS wires need to be twisted with a certain minimum number of turns or the results could be erratic. If your crank sensor wires are straight, then you need to twist them up.

There are four things that make an engine fire: Fuel, Air, Spark and TIMING.

FUEL:
-Check injectors with noid light to verify all are getting pulses
-Check fuel pressure value and leak down
-Pull the fuel rail and make sure all injectors are, in fact, spraying

AIR:
-Throttle is open, IAC functioning, etc

SPARK:
-Pull the wire off each plug, put a screwdriver into the socket and hold the screw driver shaft within 1/8" of engine metal. You should see the spark jump. It should be bluish purple like a welding arc.

If you have all the above and your engine still won't start, then you have a problem with spark TIMING. With a DIS, almost the only way to do this is to have the wires going to the wrong cylinders. Check your shop manual to see where the coils go on the DIS brick. Even if the coil is labelled with the cylinders it services, the spark won't go to the right cylinder if the coils are in the wrong location on the brick.

FP=45/50 holds.

Plug order is correct.
52 36 41
6 4 2

5 3 1
Back of car
All injectors flow and do not leek.

Never cut/spliced CPS(Checked before install) Factory twist with ground/interference wire

Got spark on all 6. Spark is blue to wight with orange/yellow around it.

NO vac. leeks.

I'll get vid. tomorrow.

Coils in this order:



Make sure your perspective and POV is right.

^^^ Thats what I have to^^^( Im standing at the back of the car.)

I have three videos. Cold start and run, Run two and a short WOT vid. Its acting ok in the first vid. It starts its shit in the second vid. and after its warm it really shows its ass in the third. in the WOT vid. it backfires thru out the whole rpm range. There's two exhaust leeks. One at the rear many. And the big one at the down pipe. the other thing I dont like is the pore response it has. Probably a byproduct of what ever is causing the BF.

http://www.youtube.com/watch?v=mfAC2MQmcR4

http://www.youtube.com/watch?v=fr8EryUrkXM

http://www.youtube.com/watch?v=9Rgs4B2g1_o

Nobody... Ok. Well i went ahead and changed the coil packs. no change. I did notice that if you (When cold) barley touch the gas it will hesitate and sometimes die. Its still hard to start when cold. Backfires at random and at wot.

yea its definately backfiring. Your timing is off. I wonder if a bad coolant sensor could cause this? You really need to hook up a scanner or ALDL or something and see what the sensors are reading. If all that checks out, then it could be the ICM, maybe a bad ground on the ICM, or the computer is fubared.

I am guessing you just swapped over to 7730 and using the TGP prom right? Not an aftermarket custom prom?

Your setup looks sweet as hell too.

I'll check the grounds. Yea its a 7730 but I got the chip from a friend. Its not the original TGP chip its custom burnt. I'll check the coolant sensor as well. whats a ALDL? Will any scanner work? Im glad you like the set up. I just wish it ran as well as it looks! Lol.

Forever-Fiero wrote:I'll check the grounds. Yea its a 7730 but I got the chip from a friend. Its not the original TGP chip its custom burnt. I'll check the coolant sensor as well. whats a ALDL? Will any scanner work? Im glad you like the set up. I just wish it ran as well as it looks! Lol.

Who burned the chip and what did they play with?

Are the wires from your crank sensor to your ICM still twisted?