ALDL fuel pump test?

[ChevyTech]

Originally Posted by ChevLoRay

This is a thread to bookmark .... .... Thanks ChevyTech for the info!

Thank you ChevLoRay for the complement.

Noid light shows no flashes on either injector at any time, key in either position.

Test light shows power to the red wire and white wire (red on passenger injector, white on D/S) when key is "on".

This sounds like a bad distributor module.

The computer needs to receive a distributor reference pulse from the distributor module to trigger the injectors.
It is possible for the module to produce spark without the computer getting a reference pulse. A bad distributor module or wiring between the module and the ECM/PCM can cause this.

The distributor module has a startup mode, which it runs on up to 400 RPM, and a run mode above 400 RPM. When these modules are failing sometimes the ECM does not receive the signal it needs to trigger the injectors in 1 or more of the distributor module modes.

With the key on there should always be power at the injectors. The ECM grounds the other side of the injector, to make the injector open.

[TennesseeZ]

Originally Posted by ChevyTech

Thank you ChevLoRay for the complement.



This sounds like a bad distributor module.

The computer needs to receive a distributor reference pulse from the distributor module to trigger the injectors.
It is possible for the module to produce spark without the computer getting a reference pulse. A bad distributor module or wiring between the module and the ECM/PCM can cause this.

The distributor module has a startup mode, which it runs on up to 400 RPM, and a run mode above 400 RPM. When these modules are failing sometimes the ECM does not receive the signal it needs to trigger the injectors in 1 or more of the distributor module modes.

With the key on there should always be power at the injectors. The ECM grounds the other side of the injector, to make the injector open.

I had the original module tested, and it tested good 6 or 8 times.

I also installed a new Borg Warner module, which is in it now, and altho I understand that I may have one bad module that tested good, and then replaced it with a NIB module that also was bad, I kinda doubt that has happened.

Is it possible that there is a bad connection or broken wire in the connection between the module and the ECM, and if so, how would I test it?

[ChevyTech]

Is it possible that there is a bad connection or broken wire in the connection between the module and the ECM,

Yes

and if so, how would I test it?

The best and easiest way is with a scan tool checking the rpm signal when the engine is cranking.

You could disconnect the computer and distributor and do testing with an ohm meter.

There is always the possibility that the computer is causing the problem. This is very rare.

Did you look closely at the terminals in the connector for the distributor module? Sometimes they get corroded.

[TennesseeZ]

Originally Posted by ChevyTech

Yes

The best and easiest way is with a scan tool checking the rpm signal when the engine is cranking.

You could disconnect the computer and distributor and do testing with an ohm meter.

There is always the possibility that the computer is causing the problem. This is very rare.

I remember when the ECM first came out, seemed like it was blamed for everything, altho it was seldom the real problem. Altho I have seen them go bad.

I'll see what I can do to get a scan tool. If I have to buy one, what would you suggest for a versatile quality scanner? I could probably go $200 or so.

Did you look closely at the terminals in the connector for the distributor module? Sometimes they get corroded.

No, but I will tomorrow. I will also spray all connections with the contact cleaner, and unplug, inspect, and spray the ECM connections when I can get to it.

[68C15]

I apologize. I didn't get a chance to grab the book today. but since you have power at the gray wire while cranking it would be a lost cause anyway.
noid light is NOT flashing while cranking but you do have spark? the ECM is not commanding the injectors to spray. testing fuel pressure is not necessary, especially if it runs after starting with ether.
during cranking the ECM gets a signal from the CRANK fuse telling it of operator's command and to let the module control primary ignition. when the ECM sees 400 RPM it takes over ignition control and begins injector pulsing. it sees the engine speed on the purple/white wire. module recieves signals from pick-up coil and sends it out to ECM on this P/W wire.
now, here's where it may get interesting based on my past findings. a rusty pole piece (star shaped magnet attached to dist. shaft) can create a weak signal to the module due to rust inhibiting the magnetic field it induces in the pick-up coil. this makes for an extended cranking before engine starts. also a cracked pole piece will do the same thing. how I am relating this to your case is you mebntioned how it starts with ether and runs fine but won't restart without assistance. the ether is simply another way of introducing fuel to the already existing compression, air, and spark. this in turn get the permanent magnet generator (pole piece) spinning faster which anyone who understands magnetic fields will tell you makes for a stronger field (signal) to the module/ECM.
in short, check the dizzy for rust and/or cracks in these areas.

I use a lab scope to diagnose these at work but in the field it takes a different and more hit-miss approach.

[joe231]

subscribed to this one, great info guys

[TennesseeZ]

Tonight I removed the dist cap @& rotor, and located the pole peice. I inspected it and saw no cracks or damage, only what I would call normal very light "rust", not even really like rust, more like oxidation.

I cleaned it with a brass wirebrush, removed the module (again), checked the prongs, all were straight and looked good to me. I inspected the connectors inside and out, and saw no damage.

Replaced everything, turned the key to run, listened for the FP, heard nothing.

Turned the key to start, let it turn over for probably 30-40 seconds, (yes, a really long time), the engine did not start.

I shot a dash of ether in the TB and it fired right up.

Headed to O'rileys now to see if they have a scan tool.

How much voltage is the purple/white wire supposed to send, I assume since it's for the ECM it's probably lower than what should be read with a test light and will require a multitester?

[68C15]

things are getting confusing now so I figured I would go back to the beginning.

Originally Posted by TennesseeZ

I made a rather long trip a couple nights ago and ran the transmission low on fluid without realizing it. I had driven 50 miles @ 55 or so without stopping, when I had to stop and start again it changed hard and slipped a little. Had to drive 2 miles to get some fluid, put a quart in but still did it. Drove it 3 miles and parked it, next morning it turned over but wouldn't fire.

knowing that in 93 they started using solenoids to control shifts and pressure I am storing these symptoms in memory.
also last night you said you had power on the gray wire during cranking, and key on. but you say you have no fuel pump operation. you also say you can give it ether and it will start and run. is there by any chance other symptoms/problems you have noticed?

I am strongly leaning to either a power supply or ground issue somewhere. I'll do some reading here, try to remember the 93 GM truck book tomorrow, and get back to you.
I apologize for being slow to respond. good news is that today I figured out both of my hair pullers at work so now I can devote more to your cause. one was a 97 K2500 7.4 with progressive random missfire that 3 other shops threw up their hands and the other was a 94 Eldorado security system problem complicated with a bad injector harness ( damn mice) and customer trying to fix it himself first. 3 years in storage-back burner to boot.

[ChevLoRay]

Originally Posted by 68C15

good news is that today I figured out both of my hair pullers at work so now I can devote more to your cause. one was a 97 K2500 7.4 with progressive random missfire that 3 other shops threw up their hands and the other was a 94 Eldorado security system problem complicated with a bad injector harness ( damn mice) and customer trying to fix it himself first. 3 years in storage-back burner to boot.

I don't know if being the go-to guy when things go down hill is good, or not. On one hand you should feel good that they think you are smart enough to figure those bad ones out. On the other hand, the idea that someone finally figured out that they DON'T know enough to fix it and gave up, only for you to have to start all over (at times) is enough to make you pull your hair.

It's at times like that when you want to be paid by the hour for your labor and not have to do it for book time.

Then, there are those times when the "boss" tells you what he wants you to do, and you do it, only to find that he was wrong and you have to find the problem and fix it. Been there, done that.

[TennesseeZ]

Originally Posted by 68C15

things are getting confusing now so I figured I would go back to the beginning.


knowing that in 93 they started using solenoids to control shifts and pressure I am storing these symptoms in memory.
also last night you said you had power on the gray wire during cranking, and key on. but you say you have no fuel pump operation. you also say you can give it ether and it will start and run. is there by any chance other symptoms/problems you have noticed?

I am strongly leaning to either a power supply or ground issue somewhere. I'll do some reading here, try to remember the 93 GM truck book tomorrow, and get back to you.
I apologize for being slow to respond. good news is that today I figured out both of my hair pullers at work so now I can devote more to your cause. one was a 97 K2500 7.4 with progressive random missfire that 3 other shops threw up their hands and the other was a 94 Eldorado security system problem complicated with a bad injector harness ( damn mice) and customer trying to fix it himself first. 3 years in storage-back burner to boot.

Hey, no need to apologize, I'm grateful for everyone's help, however and whenever it comes. I really appreciate everyone taking time to try and help me figure this thing out.

That said, I have noticed that the truck sometimes shifts into a lower gear than it normally needs, when pulling a slight grade, a grade that it will normally pull in OD no problem. When this happens it seems there is no power, depressing the accelerator way more than I should have to makes very little difference. This first happened in March? when I was on the way out here, pulling a fairly light trailer, probably under 1000# total weight.

This would happen on the Interstate when pulling a slight grade, or a medium one. There aren't any real hills in southern Illinois or Missouri.

I don't recall it doing that again until recently, I have noticed it 2 or 3 times in the last 3 weeks or so.

Also the engine "stutters' very frequently when gas is first applied, as leaving a stoplight. Like there's a dead spot just off idle, and when I'm rolling very slow, like 5 mph, it "surges", giving it just a tiny bit more gas solves the surge.
This is like 1/8" accelerator, and about 1/4" accelerator seems to get it past that point. That is true for the rolling surge, and the stoplight stutter.
Both of those are very regular observations.

As for the transmission: I have checked the fluid, it is brown and smells somewhat burned. I topped it off to the normal level, and test drove the vehicle, it changes out of park very hard, also into reverse very hard. On the test drive, in OD, it holds 1st way too long, only shifts up when I take it to @3000 and let off the accelerator. Then in 3rd it slips noticably. I have discovered that it can be driven in 2nd (gearshift in 2nd) with the only problem being the hard shift into gear. It seems to shift normally between 1st and 2nd, (with gearshift in 2nd) then I keep it around 20 mph, on my trips to the parts store.

I'm pretty sure the 3-4 clutch pack? is shot, and will require a rebuilt or replacement transmission, but I have not mentioned that or done anything much besides look at prices and inquire about labor charges.

I figured I'd better get the cranking problem sorted out before I put a transmission in it.

Having read so much on this forum about the changes that occured in the early 90's with the computer controlling more and more, I have wondered if all my problems could be ECM or sensor related, but I have not touched the ECM.

I did get contact cleaner last night, and had planned on using it on all the connections in/on the distributor, and the ECM connectors, but forgot I had it when I had the module out tonight, and have not unplugged the ECM yet.

Wow, this is gonna be a long post!

[ChevyTech]

I am curious about what you find to be wrong with your truck.

I sure I am not the only one waiting to see what fixes it.

[68C15]

Originally Posted by TennesseeZ

sometimes shifts into a lower gear than it normally needs, when pulling a slight grade, a grade that it will normally pull in OD no problem. When this happens it seems there is no power, depressing the accelerator way more than I should have to makes very little difference. This first happened in March? when I was on the way out here, pulling a fairly light trailer, probably under 1000# total weight.

This would happen on the Interstate when pulling a slight grade, or a medium one. There aren't any real hills in southern Illinois or Missouri.

I don't recall it doing that again until recently, I have noticed it 2 or 3 times in the last 3 weeks or so.

these symptoms make me wonder if your tranny is not electronic. do me a favor today and look if there is a vacuum line/hose leading the the rear.

[68C15]

Originally Posted by TennesseeZ

Also the engine "stutters' very frequently when gas is first applied, as leaving a stoplight. Like there's a dead spot just off idle, and when I'm rolling very slow, like 5 mph, it "surges", giving it just a tiny bit more gas solves the surge.
This is like 1/8" accelerator, and about 1/4" accelerator seems to get it past that point. That is true for the rolling surge, and the stoplight stutter.
Both of those are very regular observations.

"stutter" and "dead spot" contradict each other in my mind. a stutter would feel like a missfire and have a measurable frequency whereas a dead spot would feel like the engine is doing nothing.
stutter makes me wonder about ignition and dead spot makes me think EGR action, bad spot in TPS.

[ChevyTech]

Originally Posted by 68C15

these symptoms make me wonder if your tranny is not electronic. do me a favor today and look if there is a vacuum line/hose leading the the rear.

If the vehicle is as it came from the factory, being it is a 1993 would make it an electronically shifted transmission, shifted by the PCM.

[TennesseeZ]

Originally Posted by 68C15

"stutter" and "dead spot" contradict each other in my mind. a stutter would feel like a missfire and have a measurable frequency whereas a dead spot would feel like the engine is doing nothing.
stutter makes me wonder about ignition and dead spot makes me think EGR action, bad spot in TPS.

Maybe "stutter" was a poor choice on my part. It's a dead spot in acceleration, I was thinking TPS too, but I have replaced that sometime last year too I'm sure.

[TennesseeZ]

Originally Posted by 68C15

these symptoms make me wonder if your tranny is not electronic. do me a favor today and look if there is a vacuum line/hose leading the the rear.

Sorry for the late replys, I worked 15 hrs today.

You mean like a vacuum modulator? Nope, couldn't see one.

AFAIK, it's all factory.

[68C15]

can you PM me your phone #? I have time today and the book is on my desk at home here. I have more questions for you.

[TennesseeZ]

Originally Posted by 68C15

can you PM me your phone #? I have time today and the book is on my desk at home here. I have more questions for you.

Done.

[TennesseeZ]

I now have a multi-tester, had a little daylight left when I got back tonight so I have removed the glovebox and unplugged the connector on the ECM, and the connector on the module. Tomorrow early I'll check for continuity on the purple/white stripe wire.

I did notice a small scuff on the purple/ws wire as it leaves the module connector, just a worn spot where it's been rubbing something it looks like. It does not appear to be all the way thru the insulation, just maybe halfway, but it's there. I'll twist and turn it there when I test tomorrow to see if there's a break.

[68C15]

mark this one as fixed. the TPS was bad and giving an extremely low voltage. hence the ECM having a brain fart. when it looses the TPS signal it fail-safes to the CKP and MAP signals to stay running. that explains his low power (ECM doesn't see driver request for acceleration) and late soft 3-4 shift as well as the high line pressure symptoms. it pays to know theory and operation as well as getting the whole story from driver.

[TennesseeZ]

Yep, I've driven it some since the TPS replacement, all seems good. Ut cranks like it should, seems to shift like it did (WHEW!!!!), all I need to do now is put it back together and drive it on the open road, all the driving I've done so far has been in town, under 35 or so.

I just changed the transmission filter and fluid just to be safe, and because it was time, and changed the oil and filter while I was under there, so that's done for now too.

I want to give a HUGE thanks to all who have replied in this quest to help me figure it out, 68C15 is the one who called me and spent his valuable time on a Saturday nite figuring out what the problem was, and suggested the TPS, and ChevyTech responded very quickly in the beginning, and stayed with me throught the thread, and has helped me learn a great deal in this and numerous other threads.

I just can't thank these two enough, for taking thier time to help not only me, but everyone who asks a question they can help with. There are so many knowledgable people on this board it just amazes me sometimes. I have learned a bunch here, I had no idea the computer controlled so much on this truck.

Thanks again fellas, you are part of what makes this the best site on the 'net, as far as I'm concerned!

[ChevyTech]

Glad to hear you got it fixed.

Hats off to 68C15

It is often much harder to help people on a message board to find what is wrong then it is when you get experience what is happening first hand. One wrong interpretation and you can make wrong assumptions.

I wouldn’t want to have to figure it out away from home like TennesseeZ did.

Good job!

[ChevyTech]

I am thinking in the search for the problem an electrical connection was moved that may have temporarily fixed a problem.

Low TPS voltage should not prevent the truck from starting. The only way TPS voltage should stop the injectors from triggering is if it the computer enters the clear flood mode which would take a high voltage, as if the throttle was held wide open.

I hope the truck is trouble free, but there may be some issues that have not been addressed.

Even if there are more problems, if the transmission problem is fixed, the potentially most expensive problems are taken care of.

[TennesseeZ]

Originally Posted by ChevyTech

I am thinking in the search for the problem an electrical connection was moved that may have temporarily fixed a problem.

Low TPS voltage should not prevent the truck from starting. The only way TPS voltage should stop the injectors from triggering is if it the computer enters the clear flood mode which would take a high voltage, as if the throttle was held wide open.

I did finally get a multi-meter, and tested the blue wire. Engine not running, ignition "on", the voltage was jumping all over the place, IIRC it was mostly really high, like 6 to 9 or more volts.

Originally Posted by ChevyTech

I hope the truck is trouble free, but there may be some issues that have not been addressed.

Yeah, I think you're right, the engine is not as strong as it should be, I'm going to address the fuel pressure when I can test it, probably rebuild or replace the TB, and take a look at the EGR system as you have suggested in many threads. I have checked the distributor for excessive play, it seems to be fine.

Originally Posted by ChevyTech

Even if there are more problems, if the transmission problem is fixed, the potentially most expensive problems are taken care of.

There is still an issue with the transmission. At more than light throttle, it stays in gear too long before shifting, and the truck is sluggish when this happens, kinda like it's not revving up fast enough. But if I drive it easy, like I almost always do, it shifts fine.

But at least it cranks up and gets me where I need to go and back