Missing 3.4

[GTP091]

I had my crank sensor go one day and the car would not start. I've since replaced it but it has not run right since. It won't rev over 3000 without bogging and backfiring through the intake. I put a new ignition module on that I bought from canadaian tire ( not a delco ) and now it has a real bad ignition miss. I purchased a new delco ICM from GM for double the price and it won't start with that one in. It's like the plug wires are mixed up. I triple checked the firing order with no luck but as soon as I put the ICM from canadian tire back in it starts but with a miss and no power again (very weird).

Heres a list of the parts I've replaced since this started

Idle Air Control Valve
New Plug Wires
New MSD Coils
New Ignition Module ( I currently have three) original - non delco - delco
switched computer from 92 Lumina Z34
New fuel Filter
New Crank Sensor
Removed plenum and lower intake installed new gaskets to rule out vac leak
New Knock Sensor
New EEPROM for 3.4 40T60E

I had a shop do the cam timing. the back bank was off a couple degrees. They installed new generation cog wheels and set the timing up. There is little hesitation and the engine will rev up to 5,000 - 6,000 RPM now, but only if I really open up the throttle (sluggish to get there). The miss is still there at all RPM's and it still lacks power. If i hold the rev's at 3,000 RPM the miss is real bad. Also when I have the engine opened up at 5,000 RPM the RPM will slam down to 2,500 then back up to 5,000 like its getting choke slammed.

The only parts I have left to replace (besides the engine itself) are the TPS and the O2 sensor and I don't think they're gonna help.

The shop checked for vacum leaks and did a compression and fuel pressure check and their all good.

I initially extended the ICM harness to put it where the battery used to be and have since taken out the extended wiring (if you reroute the harness out where it usually travels it makes it with the original length). I've triple checked the wiring on this car all of it is exposed now. There are no broken circuits

If the engine backfires through the intake at 3500 RPM sometimes it will pull a code which is # 42 which according to my haynes book is :

Circuit or sytem : Electronic spark Timing (Ignition Control Circuit)
Probable Cause : Faulty Connections or Ignition Module

I think the problem may come from the fact that it won't start with a delco ICM but I don't know what's causing this.

Any help would be apreciated I love this car but it's driving me nuts.

[SappySE107]

RE: Missing 3.4

Ok, did you have the cam timing done before or after this problem started? Is the CPS sensor wire still braided as it should be? Is the new sensor an AC Delco? Checked all your grounds, especially the 2 that go to the transmission/bellhousing bolt on the back? It sounds to me like its either a bad ECM, or the wiring/cps is bad. Maybe intereference.

Oh...fuck. MSD coils. There you go. Did it do this before those coils were put on? oldskoolgp can tell you all about the MSD coils causing a miss.

[GTP091]

Missing 3.4

The engine ran amazing before all of this happened. I had the cam timing done after all of this started (cost $1000 cdn with 4 new sprockets). I took it to the shop to see if they could locate the problem they said it was out of time because the vacum was low and they fixed the timing and on the way home I noticed it could rev up to 6000 rpm like it used to but the engine still misses like a bastard with no power and at 3,000 RPM it won't hold a steady tune it just jumps around over and under 3,000.

I used a drill to twist the CPS wires and installed a new connector at both ends so that whole wire harness is new. I checked it for a circuit break using an ohm meter before I put it in the car. I even bought new fuel hose and slit it up protect the wiring like it was when I took it out.

I think the root of my problem lies; like the code I get says, in the fact it won't even run wtht the right ICM in it. It only runs with a NGK ICM in it. If it won't run with a delco ICM then would that mean the ICM is not getting the right signals from the ECM or the CPS?? I purchased a brand new delco ICM for 390 cdn and the car just fires randomly without starting and it sometime backfires out the intake like its getting spark at completely the wrong time.

The wire harness from the ICM to the ECM has been removed by myself to isolate any wiring poblems and even though I cut it to extend it I know for certain that the wires aren't mixed up. purple to purple - black to black tan- tan etc I used solder and heat shrink.

The engine does the same thing regardles of what coil packs are in it - the new MSD's or the older used delcos.

I bought a used ECM from a 5-speed and switched out the EEPROM from my ECM mine is an auto. I just recently bought a new EEPROM from GM ($113) and put it into both ECM's with no change.

I've put so many new parts in it thinking oh maybe it's this or it s this, that I can't wait to see how it'll run when I find this little gremlin bastard. I've dumped about 2200 into this car and its only worth 6000 with new paint. Im going nucking futs..

[SappySE107]

RE: Missing 3.4

What is the number on the computer. Should be 9396 or 9693...something like that. 113 for a memcal...dear god. I could have burned you a stock chip for 15 bucks.

[GTP091]

Missing 3.4

15 bucks?? fuck!! You should ad that into your online store.

The EEPROM code is BCDY 1694 GM Part # 16194526

And the ECM is GM part # 16149396

I give GM my VIN # and I usually get two quotes for buying parts so I know their right.

I've decided I'm going to replace the TPS next because I remember dousing it in WD40 to clean it, and now that I think of it, if that oily shit got into the potentiometer it could give erronius readings to the ECM.

While Im at it I would like to change the O2 sensor because I've read on other forums about three other guys that are having the same symptoms as my car and have changed out roughly the same parts as mine except the O2 sensor.

How the hell do you change th O2 sensor with out pulling the engine? if it's anything like the CPS im gonna scream. Where is it located and how does it come out??

Thanks for your help man.

[OldSkoolGP]

It's true, I had a miss, but it never backfired through the intake. That happens on my car from time to time too, when I start it cold. We think it's fuel puddled on the cylinders and the spark lighting it to soon, hence pre-ignition and back fire through the intake. Sound to me like it may be firing too early. Lots of things can cause that, could be the CPS, could be wiring or a bad ground. But somehow the timing in the higher revs has gotten screwed. My advice, back as far as you can to where you had nothing done one thing at a time until you find the culprit. Retrace your steps, but don't do a bunch of things at once.

[GTP091]

Missing 3.4

Do any of you guys have a trick on changin the Oxygen Sensor?? I know it's between the firewall and the engine. Do you go at it from the bottom or the top? Rock the engine forward??

[napatiger]

the o2 sensor is a bitch.

that is why I pulled my engine.

but you can buy a special o2 sensor socket, it has a slot in it to fit around the wire. that is what I would do. you might be able to borrow from an auto parts store/

[GTP091]

Missing 3.4

I put my car on jackstands to look at the O2 sensor. From what I can tell it's right beside the EGR pipe. It looks impossible to get at it from the top unless the brake booster comes off. Do you guys go at it from the top, the bottom, or the drivers side wheel well??

Today I used a voltmeter to test the signals coming off of the O2 sensor, the MAP sensor and the TPS. They all check out for the proper voltages and the right reference voltag (5 volts) from the ECM.

Do you guys have any ideas why an aftermarket NGK ICM will make my car run with a miss and hesitation but 2 Delco ICM's won't even let it start? It tries too but it sound like the spark is coming at the wrong times.

The other oprion I have is too sell the damn car and buy this::

http://www.canadatrader.com/result/detailinfo.aspx?ID=11401635&pgno=1&srt=1

its a manual 5 - speed, but then I'll have to start the restoration all over again...

[Dave96z34]

His timing may be off tdc. I learned the way some gm dealers do the timing belt is rong. They put the cam lock on and use vise grips to keep the cams from turning in the front. They dont even loosen the sprockets they man handel it on and when they tension the belt it moves a few deg past tdc. I have seen it happen. If your going to do this technique you must tention the top by turning the front cams back then geting the belt on and turning it forward 2deg to your timing marks and hold it on with a C-clamp resting the end of the clamp on the radiator filler neck so the cams cant turn foward. Then turn the crank to tdc at the same tighting the right side of the belt tight then you may tighten the timing actuator. then you can remove the clamp and the cam lock. Then check your timing marks. spin the motor a few times and bring it to tdc and check your marks.

[ltlfrari]

re Missing 3.4

Ok, I don't come here often so I just came accross your post. Interestingly I have exactly the same problem with a 3.4 I put in Fiero. Same symptoms, won't rev, ignition cuts out, no power, bogs and backfires, occasional code 42, tach drops than jumps back up.

I replaced the original ICM with a Delco one as the orig was fried even though it tested good. No change.
Also did the cam timing (twice that I can remember) the right way so I KNOW it is right.

I am running a 9396 ECM and BCFA program in the chip coz the motor is hooked up to a manual tranny. I did all my own wiring (probably explains a lot !!!!) but I am pretty confident I got it right, 'cept for the fact it won't run right of course....

I hooked up one of those transparent ignition testers into the ht plug lines so I could 'see' the spark while it ran and you can see the spark actually stop when it cuts out, so either the icm is chopping the spark or the cm is, or there's a fault in the wiring between to two or to the icm.

My current thinking is the wiring to the icm is faulty. Either from the ECM to the icm or possibly even the power supply to the icm. If that was cutting out everything would keep stopping. It could even be the connectors into the icm are not making contact correctly. Just feels like an electrical problem. I checked the map connections are correct way around and I know the TPS is ok from th scan data so not much else it can be in my opinion.

My car has been sitting there like this for 18 months now so I really need to get back to working on this. I'll keep you posted if I discover anything.

Dave E

[GTP091]

Missing 3.4

I was going to replace the TPS and O2 sensor but I followed the book procedure by testing the voltage readings on both and they check out fine. Now Im back to square one with this problem again. I had a shop check the timing and they said they had alot of experience doing it and did it a better way than GM does. The only thing I can think of its the wiring like you said from the ECM to the ICM or the 12 Volt Power supply. But I've checked it a ton and theres no breaks no broken insulation. I've even followed the wire to the ECM connector plugs and used an ohm meter to test for continuity. It all looks good but my car is still gutless. I've since put the car in its cave for the winter and maybe some hibernation will make it feel better in the spring.

[ltlfrari]

re : Missing 3.4

Rereadig your first post I noticed you said the crank sensor went bad. Just wondering how you know that was the problem since although I replaced mine as well those things are pretty much bomb proof since no moving parts, just the cutouts on the crank affecting the magnetic field of the thing I think to generate the pulses.

The only othe thing I can think of is mabee the knock sensor is somehow telling the ecm there's a knock ALL the time so the ecm is cutting the ignition and/or retarding the timing to compensate. Could be electrical noise on the knock sensor wire is throwsing the ecm off.

On mine at least the sensor in the engine is still the one from when it was hooked up to an automatic. I checked the part nos between the 95 cutlass it came from and the earlier manual cars and it says same part number but it could still be knock sensor. I need some way to 'trick the ecm' to think it still has a knock sensor but actually disconnect it. Probably just need a resistor to set the correct static voltage on the signal wire.
Like you I have tested my wiring (about to do it again just to be sure though).

My car has been laid up for over a year with this problem but the wife commented on it the other day so time to get moving again I guess

Dave E

[GTP091]

missing 3.4

I found the crank sensor was the problem after I repalced the ICM and ECM and the car still had no spark. As soon as I replaced the CS the car started but with the miss I'm having now.

The thing that really bugs me is 2 brand new delco ICm on't let the car start it just sounds like the spark timing is way off and it fires a little bit. Im sure if I kind fingd the reason this happens I cwould have my car back the way it was; real big balls! It even gets hard to turn over as if the plug is firing when the piston is rising. An NGK from Canadian Tire starts my engine just fine but with backfiring through the intake and a miss and no power.

[ltlfrari]

re missing 3.4

Well I think I have fixed mine. When I did my swap I relocated the coils so I extended the wiring from the crank pos sensor (the one on the block) to the ICM. I followed the book, color coded wires etc. Should have run ok, ran like crap (same sympoms as yours).
The other day decided to swap over the wires (basically cut the wires and resoldered them to the opposite wire, yellow to purple, purple to yellow as it were).
Tonight I just plugged it in, hooked it up and tried it, Ran beautifully, no misfiring, revs all the way around the clock. I can't road test it yet (no brakes or wheels on it right now) but based on the difference just static runing it I think it will be fine (fingers crossed).
Now bear in mind that mine was a complete swap and the wiring was sitting in my garage for months before I did it so I could have picked up the wrong connector for the ICM (I think I had two three pin connectors knocking around for some reason) but I followed the book and it was wrong.
I found something on the net that says the ICM trigers on th negative going edge ofthe crank pos signal so if the wires are crossed the timing will definately be out (which is what it feels like when you drive it). Not enough at low revs to impact it too much but as the revs increase the timing becomes more critical and the difference is enought to have a major impact.

Maybe the ICM's have different pin connections, I dunno but it may be worth ten minutes with a soldering iron and some shrink wrap to find out

Hope this helps.

Dave E
http://www.ltlfrari.com <== complete engine swap info on here.