Help all gearheads 2

[RogerAS]

Hey,

Still no go.

Had a man come over with diagnostic computer.

It reported "No communication with system" and showed no error codes.

It seems either the ECM (engine control module) has failed or the wiring to it has failed.

I am a point of complete frustration.

Elvin, I will check the relay under the engine compartment fuse box. I do hear a click there when the key is turn to on position so I doubt that is it.

Oz, have had the neg battery cable off for several hours, no go.

According to the man that cam over there are only these units involved in ignition:

the crank position sensor, the coil packs, the DIS box on the intake and the ECM (aside from the grounding and power supply). If nothing else I can replace ALL of the X%$!ing boxes and it will run.

I found info on how to check if coil packs are dead, and will test, but not likely the problem as the computer shoild have shown this in error codes.

I really appreciate all the input from the posters in the other diary entry.

Any other ideas?

[luv2weld]

First, let me ask a couple of questions.

It was running just fine before you replaced the plugs and wires???

Have you put the old wires and plugs back on???

If it was running OK, then it is probably something you did, or

something you bumped or knocked loose without realizing it. Go back

over what you did slowly and carefully and look at everything. Check

all connectors to make sure they are plugged in all the way. Don't forget

to look inside the connectors to make sure you don't have a broken or

bent pin.

Also look for pinched wires.

If still nothing, then take a jumper wire--- 24 inches or so with

alligator clips on each end, and start testing each component that

you touched or worked on for ground. (Have you checked the ground

cable from the battery to the engine, and to the frame??)

Have you tested every electrical function on the truck??---

such as turn signals, wipers, etc?? Don't look at me in that

tone of voice!! I know it sounds like I've been been smoking

that Wacky Weed. But pinched wires and bad grounds are the

two hardest things to track down. Ground problems will drive you insane!!!!!

If you still haven't found it after this, let's sit down with

a cool drink and think about it a little more.

Ralph

[wiredwrong]

1st what year is it?, most diagnostic computers only work on 96 and up, also there will be a crank position sensor which was left out of your list. if the truck is 96 or up and the diagnostic computer cant communicate then I'd replace the computer, Ive never(not saying it cant happen) seen the wiring to the connector go bad, I missed all your other posts about what is going on but will look for them, Im sure you've already checked but Ill ask anyway, Have you checked all the fuses under the dash, specifically the ECM fuse, have you pulled a plug wire and cranked the engine to see if you have spark?

[oztules]

Dont like the sound of no communication with system....

Looks like it is time to go bushranging by following the coil pack leads back to the computer and see if it is trying to fire them at all.

I suspect that your packs get their input pulled to neg to fire the coil. If so we are looking for a pull to ground when they fire. (meter should verify signal or not hopefully.) It seems odd that all packs could fail as one.... so probably not the packs. They all use different inputs, (can't all have pinched wires) but the pos and earth are probably common to all of them, so check for b+ at the coil/s.

If we have b+ and b- but no signal, it looks like we are looking for an input failure to the computer from a periferal, or the b- line to the fet bank in the ecu. The chip would seem to be ok if the injectors are running ok.

Had the fets failed, they normally fail short, so the sig line would look like ground from the coils viewpoint, and I would expect the coil pack to heat up.

so really need to establish b+ and b- and signal with respect to the coils b- or b+ pins before we can conjecture further. If there is no b+, does it go direct to the ecu, or  is there an inline fuse or interrupt that is conning us.

I assume it uses the crank posn sensor  for the fuel injection as well as the ig timing, so poor connection to the new one you put in is unlikely. You have replaced the DIS box, so scratch that (but check for continuity to the ecu anyway).

Some of these rotten ecu's read the back emf of the coil, and if you have pulled the plug to check for spark, it may read it as a misfire, and won't address that plug/s again without a reset. Thats why I suggested the reset, in case yours was one of these, and you had cranked without the leads etc.

My work with ecu's is very limited (thank goodness), but so far only dry electro's and 1 injector transistor in the ecu is the limit of my experience with these confounded things.

Mine looks like this one: http://www.otherpower.com/images/scimages/5171/suzuki_computer.JPG

I'm guessing yours is a whole lot more complex.... (fets for the ignition which mine doesn't, but four transistors for the injectors, which I do have..... most of the time anyway)

At this stage, until you can verify b+ at the coils, I am hopeful of an interuption of power to the coils. If b+ is present, but no signal, then ecu or a kill signal sent to the ecu by some sensor (no oil, no brakes etc) that would tell it that it is dangerous to start.... or a sick ecu....

There should be a limp home setting somewhere that the computer defaults to if any other sensors are calling for help, but this is out of action too... odd.

You don't have an alarm in this thing that allows cranking but no ignition for the car thieves do you....

best of luck ........oztules

I was forced to fix mine.... no tow trucks here..... or any where to take it to either.

[zap]

Hey Roger, maybe Elvin is on to something with his comment in your first post.

I only did a short stint wrenching on vehicles for a living but have had my head under hoods for a long time and a phrase I've always heard, only half joking... "It's always the ground!"

Good luck with it.

[JW]

I just briefly read you first diary entry on this, I understand after changing plugs and wires you have no spark now.

I have one of these as well, the 8 sparkplug 4cyl.

Check to see if your camshaft sensor is ok... Mine sets a code, says its not working but the engine runs ok. It may not be related to your tuneup work at all, just a nasty conisdence. By the way, the dealer told me the dam thing is only asseable with the transmission out(ouch). But they may be wrong and it could be easier to get to. also try to wake up the ECM by disconecting BOTH battery cables and shorting them together- to clear any codes.

best of luck with that. its a tough one.

JW

[vawtman]

 Hi JW

 When i had the problem with the timing belt skipping and shutting down the spark.I always wondered how the ecm knew that.Camshaft sensor seems logical and Roger probably knows where it is.Since he rebuilt it.

 It is weird though that all this happened from a simple tune up from a guy with Rogers experience.But .... happens.

 Best wishes Rog if you read this.

 Mark

[vawtman]

Hmmm,I wonder if the plug wires were crossed at some point how the ecm would react to this since it's a little 4 popper 8 binger overhead cam?

 I got one i will test at at a freinds house tomorrow if needed.

[RogerAS]

OK,

B4 going to work today I unhooked both battery cables, took the connector loose from the ECM and let 'er sit all day.

When I got home this afternoon I sprayed some contact cleaner on the ECM connections and brushed out some gunk, very small amount of corrosion.

I checked the ground snap connector lead UNDER the engine compartment fuse box and found some more corrosion there as well. Cleaned that.

I tested between B+ on the front coil and coil lead #1 & #2 for primary resistance and both are within specs (.3 to 1 ohm) and reads .7 on both terminals opposed to B+.

HOWEVER! the secondary reading is OPEN on both coil leads. They are supposed to read between 6,500 and 11,500 ohms.

So after much ado the coil pack that fires on compression (power) is bad.

To confirm this I pulled #1 power spark plug and cranked the engine with that plug out but attached to the boot. No Spark. I pulled the boot off #1 exhaust plug and inserted the spark plug I removed into that. It sparks bright blue when the engine spins.

This is sortta odd as neither coil pack would make a spark earlier. Do you think the DIS module was bad and overloaded the coil somehow?

I may rob the rear coil pack and replace it to the front position just to get the old machine moving again.

I want to offer a very deep and pronounced thanks for all the help and advice you folks have provided. This is just one example of how great the membership here really is. You guys are the greatest!

I will post a follow up when I have things settled out. What a stressful few days over a stupid old pickup!

[RogerAS]

ARRRRGGHHHH!!!

I switched the coil packs around, and still no go.

I foresee a call to a tow truck.

[ghurd]

Toyota PU, 4 banger, 1992?, 150K?, and Red (I recall that for sure!).

It had spark. Gas. Air. Everything.  Worked perfect, except it wouldn't start.

Same problem.  Wife drove it from the front of the house to the back, shut it off, no problem.

That was that.

Three weeks. Called everybody I could think of. Changed everything I could think of.

Bought a new ECM. Not the problem. And not returnable, BTW.

Towed it to the dealership.

Over 2 weeks to diagnose...  Timing chain jumped a tooth.

Two weeks for the dealer to figure it out? Crap!

Just a thought.

G-

[Nothing40]

The comment about the 8 plugs in a 4cyl engine sparked a memory of a Friends Nissan truck...

He was having some minor issues with it and thought he'd reset the ECU:

"also try to wake up the ECM by disconnecting BOTH battery cables and shorting them together- to clear any codes."

DO NOT!!!..do this..DO NOT!!

My friend did this on his older Nissan,and ended up scrapping it.

Shorting the battery cables together somehow fried his ECU and everything. The dealer's estimate to fix it was more than the truck was worth! It was towed to the scrap dealer the following week.

[elvin1949]

Rodger

  one more thing.The ecm is under the kickpad on the passenger side [this is for other folks].

 Be sure the ecm is grounded to the body,i think it has a ground wire that goes under one of the mounting bolts.

  Then make sure the motor is grounded to the body.

That will be a wire from the back of the motor to the firewall. You have another ground from the neg battery post to the motor block,and another from the motor block to the frame. They all have to be solid.

  Then go back and check the relays again,there is more than one,just hearing a relay click does not mean anything there is more than one.

  Got to go back and do more reading and thinking.

As an aside i made my living working on Fords before i became unable to work.Been a while.

later

Elvin

[JW]

When I was in collage, they tought us that the DIS coil packs will destroy themselves if the secondary circuit is open and the engine is cranked over. These type of coils can make over 100k volt. this can breakdown the insulation in the coils causing a internal short circuit.

 Very rarely I have had heard of someone frying an ECM by trying to internally short the (memory)capacitor inside. But it can happen. Personally ive never given it a second thought. Never had a problem. To be safe it is recomended that a resistor is used to short the batt leads together. this will more slowly discharge the cap. Air bags have the same type of mechanism. to  more accuratly describe what im saying, physically remove the battery from the vehicle, then short the leads. And make sure there are no alternate power sources on the system, such as a cell phone charging, anything like that.

JW    

[LarryDalooza]

I have had a couple of 2.3L in an 85 and 94 Tempo...

I had used up at least 4 ignition modules. They are cheap to replace.

Lar.

[Gog]

I had something similar on my old 8 plug nissan.

I did a rough check by pulling out the plugs and cranking it over fast to see if the tacho (rev counter)

showed any thing , it stayed on zero revs.

It turned out to be the cam position sensor in the distributor.

A second hand distrbutor had it going again for about a year, but I pushed under the trees when it did

it again.

just a thought

Keith