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continued injector signal pulse failure issues

4xcrazy

4xcrazy

3/4 ton status
Joined
Oct 31, 2003
Posts
9,485
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Location
Elma, Washington
I don't even know where to go now. After all the trouble shooting and replacing parts on this motor, I'm running out of ideas and starting to realize why alot of guys get rid of the TBI and go back to carbs.

I have replaced the ignition control module with 2 used ones. And finally broke down on Saturday and bought a brand new one. It started and ran all day so I figured I'd go against my better "gutt" judgement and start heading back to Phoenix from Indiana. Made it to St. Louis.MO.

In previous attempts at figuring out this problem, I have also replaced the pick up coil in the dizzzy, I have also removed the entire engine harness and checked for any signs of a problem, nothing crazy abnormal so I reinstalled it. I have also swapped out the main computer with a borrowed one.

I have constant fuel pressure, new pump, had a gauge on it during this stall problem awhile back. It will fire every time with a couple of quick shots of ether, it is definately a fuel injector pulse signal delivery problem, both injectors will not spray, and I have had a noid light on the connectors to determine the lack of signal.

What an I missing.

I'm only bored now, so I'm gonna head back out and double check the grounds, if that doesn't do anything I'm going to remove the distributor and give it yet another inspection, tear it apart, have the ICM checked out, I dunno,,,

After having to sit in that truck for almost 14 hours under an overpass on the side of a very busy freeway, in 95+ degree heat plus high humidity, with a couple of my cats in the truck with me, along with my turtle tank, all my crap basically in the truck and a small trailer, then having to have money and a truck borrowed from an uncle to come recover this thing....this just cost me alittle over $600 I am now finding out.

I am having a difficult time NOW with deciding on whether or not it's going to be worth keeping this truck running, with yet more money and time which I really don't have, or just to retire it and part it out. Thats the only way I would be able to get anything out of this thing is through parts only.

Something else please, please don't read my posts about this problem as a rant or fed up type screaming, it's actually quite the opposite, i'm actually pretty bummed about this, I have never had this kind of ass-kicking problem before, my brain is about fried from the mind visuality of the circuits, sensors, electronics, whatever, just tryring to think of anywhere there could be a bad spot or a problem. I'm about dead thinking about this for so long, and now unfortunately, even after a "possible" repair, I'm still not going to be able to trust it like I used to.

Any ideas or thoughts?

Thanks a bunch. :bow:

Only other Idea I have is to buy a brand new engine harness, but with the lack of recent good luck, I am having a hard time coming to terms with a nearly $400 wiring harness and have that still not be the issue.
 
So you are not getting an injector pluse? I will post up the trouble tree for you to run through it is pretty helpful. Lucky the GM TBI system is pretty easy to figure out normaly. Do you have a test light and a volt meter with you?
 
1979jimmy350 said:
So you are not getting an injector pluse? Do you have a test light and a volt meter with you?
Click to expand...

No injector pulse signal to the injectors, sometimes it works, most of the tme it doesn't, which is why i went ahead and bought the brand new ICM in the idea that maybe those older ones were heating up and shutting down or something.

I was told that the 4 wires coming off the ICM that control various things, one of them being that pulse signal, were a lower voltage circuit, I asked about this because those wires seemed to be getting pretty warm during idling, not sure if it was just engine heat or what, but they just seemed warmer than wires should be.

Yes I do have a test light and a volt meter, although now I have to go dig the voltmeter back out of the trailer. :-P
 
injector.jpg

This is assuming that you are getting no injector pulse, if anything is unclear just post back up, ill keep checking often

injector.jpg
 
4xcrazy said:
No injector pulse signal to the injectors, sometimes it works, most of the tme it doesn't, which is why i went ahead and bought the brand new ICM in the idea that maybe those older ones were heating up and shutting down or something.

I was told that the 4 wires coming off the ICM that control various things, one of them being that pulse signal, were a lower voltage circuit, I asked about this because those wires seemed to be getting pretty warm during idling, not sure if it was just engine heat or what, but they just seemed warmer than wires should be.

Yes I do have a test light and a volt meter, although now I have to go dig the voltmeter back out of the trailer. :-P
Click to expand...

Just a sanity check did you use the white grease on the bottom of the ICM when you installed the new one?
 
Thanks for that, alittle difficult to read on the phone, but i can and will manage. :-P

I'll try & follow what it's saying and see what comes up.

Thank you very much
 
Basically the same as that test chart but check the following:

ECMA or ECMB fuse is used to power the injectors. Make sure it has a proper connection in the holder. I have seen it in the past where the fuse had an intermittant connection which would kill the truck dead. Make sure you have 12V on one side of each injector.

The other side of the injectors is a ground path switched by the ECM. Check to make sure the ECM grounds are solid. On the TBI trucks, you can find them on the rear pass side of the engine and up by the thermostat studs. It is not unheard of for the ECM's injector drivers to fail, don't count it out just becuase everything else appears to work, esspecially if it is intermittant.

Make sure the wire from the ICM to the ECM is solid. You can test it my momentarily grounding the white wire off the ICM to make sure the ECM runs the fuel pump. The black / red wire off the ICM should be a solid ground, check it for excessive resistance. The tan / black wire is for setting the timing, your engine's timing should change when you un-plug that connector. The purple / white wire is the reference pulse that the ECM uses to determine where the timing is at based off the pickup coil in the harness. Just make sure that wire is solidly connected.

Also, take your distributor cap off and remove the rotor to get a good look at the pickup coil. They can fail too and you'd think it was a bad ICM.

If you have spark, but you don't have any injector pulses, then I'd suspect that your ICM is fine and would be suspecting a bad connection to the ECM from the ICM, or a failed ECM.
 
Most anything is fixable given enough time and effort.
And this is probably a simple problem and reasonably cheap to fix.

Once we find it.

The only way to decide whether to fix or scrap, is to see what you will have if its fixed.
If it were running well, and you could depend on it, would it be worth keeping?
If not, start shopping for customers for the parts.

If so, then lets fix it. If nothing else, the satisfaction of being to say it did not whip your butt is worth a lot.

First, lets check some basics. Grab a voltmeter, and check the battery voltage with it running and everything on.
I have been seeing a rash of over-voltage problems lately.
Under voltage would be noticeable. Dim lights, hard cranking. But the alt might be drifting too high and causing a component to overheat.

What year is it again?
Most of the wires on these trucks are not critical except for the fuse links.
Which means we can add temp. wires to bypass parts of a suspect harness wire.

If we are sure the injectors are not firing, then we can do some testing. I will check my schematic, and we can bypass the two injector wires to see if that helps.
Also, we can put some test points in the harness to check for pulses that should be there.

If you don't have a 'scope, I can clean up my Fluke Scopemeter and let you borrow it. Then we can see if the pulses are there when they should be.

Heck, we can record a pulse train, and post it here to see if it looks right.

I'm a little busy right now, but if this thing gives us too much trouble, I might just make it a ......Project.....

Remember the old Hulk saying?
Don't make me angry, you would not like me when I'm angry.....

There are several pieces of equipment that I worked on years ago.
Their owners swear to this day, that if it starts acting up, I can just walk by and look at and it fixes itself.
 
I seem to have that effect on EFI too, Fordum, haha!

A scope meter would be brilliant for troubleshooting EFI issues -- I am extremely jealous that you have a mobile one! Mine is a giant bench mounted turd from about the 60s...
 
Russell said:
I seem to have that effect on EFI too, Fordum, haha!

A scope meter would be brilliant for troubleshooting EFI issues -- I am extremely jealous that you have a mobile one! Mine is a giant bench mounted turd from about the 60s...
Click to expand...
Mine is not all that new. I guess its about 12 years old. Its a dual channel 200mhz monochrome unit.
I have used it a lot on various pieces of equipment.
Its got two channel scope traces, plus multimeter options. And will record a couple of minutes of waveforms.
Fluke made an automotive version, the 98 if I remember right. You see them on E-bay in the $300 range from time to time.

If I did a lot of work on injected motors, I would pick one up.
 
I'm no whiz on EFI,but have seen some similar problems on other GM vehicles at my friends shop...

One S-10 had such slop in its distributor shaft that it was whacking the rotor against the contacts in the cap!--turned out the dizzy was made of PLASTIC and had no bushings for the shaft,it was a 4.3 I think --what a peice of "engineering" that idea was!..he had just put the engine in it too,and when he heard the noise he was livid,thinking he'd been sold a junk engine!..the truck ran poorly and misfired and would stall and refuse to start again right away..a "new used" distributor solved the dliema..

Another car he had,a 1990's Olds ,a "grannys car" with only 50K on it developed a perplexing stalling issue,no fuel was getting to the injectors some of the time--a new fuel pump,pick up coil and fuel pump relay all were replaced one at a time,which seemed to fix it fir a day or two,then it would DIE on the road again!...it went to 4 other shops for "diagnosis" and none found what was the problem...then one day a kid no more than 25 came to his shop,sees the car and says "hey,I had a car like that and it did the same thing--took it to shop class at school and my teacher said to replace the injector(s),if one goes bad and shorts out,it "kills" the rest of them too..sure enough,the car would sometimes start and run great,then die whenever it felt like it..while he was there we started it up--it ran great for about 10 minutes,then died...the kid pulled the wires off one injector,and it started right up and ran on 3 cylinders (it was a 4 cyl engine)...the owner drove it several weeks before it did it again,and replacing another injector fixed it for a month or so,then another one stopped working,so he decided to visit a boneyard and just get the whole rail and all 4 injectors,and it has run fine ever since then...(after spending 250 bucks on parts,which was 50 more than the car cost him to buy!)....

So--I guess injectors can short or ground out and "come back to life" again just like an ignition module or computer can??...

I'll stick with carbs,thank you....EFI is great until things like this start driving you insane...
 
Well, after tinkering alittle more, i realized that the pink wire w/ black stripe is actually the 12v power to the injectors, so that got me nothing originally. :doah:

And further, i removed the ICM and had it checked several times, this is the brand new one, it tested fine. I did also check out a brand new distributor at the parts store, and realized the little magnetic "grabs" it does while turning is not as strong in mine as it is in the new ones, any thoughts on this? Also there just the tiniest bit of play in the shaft of mine and there didn't seem to be any at all in the new one.

Weird thing now, I reinstalled the dist. Turned the key on and can rotate the rotor by hand (not seated all the way down) and the injectors will pulse when it hits the trigger point.

So either I definately have a bad wire connection towards the back of the motor thats losing connections in the harness, or there is something funky in the distributor.
 
Just had a thought while I have the the complete engine harness on the table,,,, WHAT IF,, i'm losing the 12 volt signal to the injectors...

I reaized that I keep saying i don't have the ground pulse signal soley based on the noid light failure to light,,

I just hooked up the voltmeter to the injector plugs and realized what I originally thought were the ground wires, were in fact the 12v power wires. Unfortunately however, as i reinstalled the dizzy and did the hand spin check for injector pulse, they sprayed, i also had the 12 volts to the hot side so i really can't tell if i have a ground or hot siide failure.

But as i am sitting here with the harness on the living room table, checking the wires end to end, all connections so far are giving me readings, all ground, all power wires from computer plug to fuse panel pins to connectors. Damn this is some tricky crap.
 
I think i'll just do the original plan, new harness & new distributor and be done with it. It's GOT to be one or the other, and with the new motor I should have a new distributor anyways, this one has 260k miles on it. Probably worn out.
 
I had similar problems a few months ago....I started changing parts including the module, coil, whole distributor and the ECM. It turns out if you have your plug wires too close to the ignition wiring to the ECM, it causes a misreading...after I used a bunch of zip ties to keep the wires separate, the problem was gone.
 
Put a brand new distributor in it while I was there this past week, used the distributor oil primer shaft tool, pre-oiled everything since it hadn't run in a year, it started, ran like crap until the old fuel ran through the lines and it picked up the new stuff I had just put in it.....

idled fine for awhile, then, as before, just shuts down.. no spitting, no sputtering, just off...

Now i'm really getting confused.... what else could this possibly be...
 
Just to confirm, you are 100% sure that your fuel pressure is remaining steady at 12 PSI when the engine stalls? You've changed the distributor and ignition coil? You've verified that the 12V supply to the ignition coil is not dropping out?
 
coil stays hot, when it dies out, there are times when cranking it back over will not refire on it's own, but a touch of ether and it fires right up, until the ether is gone.

fuel pressure seems to be stable, had the pressure gauge inline when this all happens in the driveway. It does drop when the engine shuts off, like when the key is off, but when you go to restart it, pressure comes back and it still won't start. Random signal loss again.

Wondered about the injectors too, but I had a noid light plugged in the injector connectors and that's how I determined loss of signal pulse.
 
Have you visually confirmed the spark is dropping out? Maybe pull a plug and wire out and run the engine until it dies. You need to have a crisp, hot blue spark for proper ignition. Fuzzy and reddish or orange is no good.

The ECM will stop firing the fuel injectors if it looses the signal from the distributor or the ESC module. Speaking of which, have you tried swapping the ESC module?
 
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