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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15481
Experience:  Have owned a repair shop for 25 yrs.
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88 chevy 3500 5.7 tbi with 5th vin digit K. No voltage to

Customer Question

Hi, 88 chevy 3500 5.7 tbi with 5th vin digit K. No voltage to either side of injector harness. All fuses good, no voltage to injector a/b fuse. Replaced the pickup module in distributor, no joy. Good fuel pressure to throttle body, starts with gas dumped in tbi. Code 12 when service port is jumped, ses normal 1 sec flash on run position. Was running fine till was wiring trailer lights. Had key in run position for maybe 3 min. Any ideas what could kill power to the injector fuse?
Submitted: 1 year ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 1 year ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you

what fuse doesnt have power?

the ecm1?

Customer: replied 1 year ago.
The ecm is hot on both sides of the fuse, the "inj a/b" right below it is dead on both sides of the fuse, fuse tests good. No power to either wire on injectors
Expert:  Tim's Auto Repair replied 1 year ago.

ok

tell me,,does the fuel pump come on for the first two seconds when you first turn the key on?

Customer: replied 1 year ago.
evidently the fuel pump relay is ok? Also have good pressure and flow to the throttle body. I do not have a guage, but the pressure and flow are significant.. The injectors are completly dry, and no voltage. I had considered jumping some voltage from the primary side of the ecm fuse to the inj fuse for a diagnostic, but decided to wait
Expert:  Tim's Auto Repair replied 1 year ago.

ok

will it stay running when you prime it?

Customer: replied 1 year ago.
long as gas is present, yes
Expert:  Tim's Auto Repair replied 1 year ago.

ok,did you replace the module or the pick-up in the distributor?

Customer: replied 1 year ago.
One note, all started while I was rewiring taillight wires on both sides. I did have the key to run position for 3-5 min. Have since cut all wires that I had wired up to taillights, to eleminate poss of dead short
Customer: replied 1 year ago.
The wires had been cut evidently to eliminate a short in the trailer plug.
Expert:  Tim's Auto Repair replied 1 year ago.

ok,did you replace the module or the pick-up in the distributor?

Customer: replied 1 year ago.
autozone tested it bad, but had orieley check before I bought a replacement, and they tested it as good. the second test, oreiley, did not use a ground clip on the module. Replaced, used dielectric grease. The old one was crusty rusty, but per orieley, was good. Same result
Expert:  Tim's Auto Repair replied 1 year ago.

but what was you testing?the ignition module or the pick-up coil?

Customer: replied 1 year ago.
They are one in the same, 2 wire plug inside the dist, two plugs on the outside of the base of the distributor
Customer: replied 1 year ago.
2x 4.5mm screws hold it on distributor base plate
Expert:  Tim's Auto Repair replied 1 year ago.

no,,the pick-up coil can not be replaced without pulling the distributor and taking it apart

Expert:  Tim's Auto Repair replied 1 year ago.

#10

Customer: replied 1 year ago.
Then the module. Remember, it runs with a prime
Expert:  Tim's Auto Repair replied 1 year ago.

you replaced the module..the likley problem is the pick-up..you may just want to replace the complete distributer with a new rebuilt unit

Expert:  Tim's Auto Repair replied 1 year ago.

yes,,i understand you are loosing injector pulse

Expert:  Tim's Auto Repair replied 1 year ago.

if it isnt the pick-up,you may have fried the ecm[computer itself]

Expert:  Tim's Auto Repair replied 1 year ago.
Customer: replied 1 year ago.
Not doubting you, but the module was the likely culprit per the forums. The injector harnesses are supposed to be hot with key in run position, and the ecm pulses by grounding this circuit. Since we have good running with a prime, does this not indicate we have a good ignition pulse and thus good pickup?
Expert:  Tim's Auto Repair replied 1 year ago.

no,,you can have spark and no pulse

Expert:  Tim's Auto Repair replied 1 year ago.

what happens is the computer will not send a pulse unless the engine is turning

Expert:  Tim's Auto Repair replied 1 year ago.

the computer uses the pick-up to know when the engine is turning

Expert:  Tim's Auto Repair replied 1 year ago.

also,,the fuel pump

Expert:  Tim's Auto Repair replied 1 year ago.

the fuel pump only runs for 2 seconds,,when you first turn on the key,and,all the time that the engine is turning

Customer: replied 1 year ago.
But the pulse from the ecm is on the GROUND side, so the ecm grounds and completes the hot circuit from the energized injector.
Expert:  Tim's Auto Repair replied 1 year ago.

again,,it is possible for you to have fried the computer itself when you shorted out the wiring at the plug

Expert:  Tim's Auto Repair replied 1 year ago.

the good thing is,these older computers cost less than $100 now

Customer: replied 1 year ago.
If that were the case, would'nt I not have any codes, and no 1 sec pulse on jumped ecm service port? Only code that shows is 12 which is a no code, all systems check, as I understand it
Expert:  Tim's Auto Repair replied 1 year ago.

make sure the ecm fuse isnt blown

thanks

Customer: replied 1 year ago.
The ecm fuse is hot on both sides with key on run, and passes continuity test when removed
Expert:  Tim's Auto Repair replied 1 year ago.

no,,you wouldnt get codes because the computer wouldnt know anything is wrong,because it doesnt know the engine is turning

Expert:  Tim's Auto Repair replied 1 year ago.

replace the pick-up or the distributer

Customer: replied 1 year ago.
you believe then that the pickup is causing me not to have voltage when in run position? I found at least 6-10 forums that said this was supposed to be hot with key in the run position and no cranking.
Expert:  Tim's Auto Repair replied 1 year ago.

yes,,i think it is either the puck-up or the ecm[computer]

Expert:  Tim's Auto Repair replied 1 year ago.

there is nothing else if the wire harness is good

Expert:  Tim's Auto Repair replied 1 year ago.

i know you read the foums,but,we know what isnt wrong,the module,because you replaced it.

Expert:  Tim's Auto Repair replied 1 year ago.

replace the pick-up

thanks

Customer: replied 1 year ago.
OK will hold off rating pending results, please confirm in the meantime that
A, voltage to inj harness when in run, not crank, per an absolute total of all forums I visited, defintately well over 6.There was no discrepancy here, all said should be steady, hot in run position
B. either of these parts could kill the voltage mentioned above, as all forums said the ecm only grounds the circuits of the injectors. Found 3 instances of dead ecm, one of which had no SES light and no codes, and all 3 had voltage at the injectors. Trying to confirm, because with this charge, plus a pickup, plus an ecm, I will have paid a ton for nothing if this is incorrect. If you are absolutely confident that alll of these forums were wrong, I will get a pickup tomorrow.
Expert:  Tim's Auto Repair replied 1 year ago.

the forums arent wrong

Expert:  Tim's Auto Repair replied 1 year ago.

the module can do this,,but most times whe nthe module does this you will also loose spark,,again,you say you already tested/replaced the module,,so,we pretty much can rule out the module,,right?

Expert:  Tim's Auto Repair replied 1 year ago.

so,,that leaves us with the pick-up[this is likley] and the ecm

Expert:  Tim's Auto Repair replied 1 year ago.

there isnt anything else

Expert:  Tim's Auto Repair replied 1 year ago.

i can also give you the fuel injector wire diagram,,stand by

Customer: replied 1 year ago.
Note for instance, this just answer that states should be hot in the run, not crank position
http://www.justanswer.com/chevy/2huov-1992-chevy-1500-pu-350-truck-won-t-start-until.html#re.v/327/
I will find the link of the system with the completely dead ecm with no SES and still had voltage at inj
Expert:  Tim's Auto Repair replied 1 year ago.

PLEASE COPY AND PASTE the link below to your browser, I have uploaded more info on this there please copy and paste the link below to your main browser[INTERNET EXPLORER or FIREFOX]

.

https://www.dropbox.com/s/cymosdf16ns5k3e/1031-88-chevy-ECM.doc?dl=0

.

if the link doesn’t work that way, try it this way

thanks

.

www.dropbox.com/s/cymosdf16ns5k3e/1031-88-chevy-ECM.doc?dl=0

.

If you are satisfied with my answer, Please Rate my answer by clicking the rating button so I can get credit for my work. I’m not always going to be giving you good news, so please don't let this stand in the way of you accepting my answer. .it does not cost you more money and we will still be able to communicate, ,.please understand, i can not see, hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated.. if you are not satisfied with my answer, please do not leave bad feed back ,i will gladly opt out and let another expert handle the question. .if i have sent any diagrams, please print them. .sometimes you may need to right click the image [,then save picture as]to save it to your computer so you can open it with your picture program...Please ask if you need more help

Expert:  Tim's Auto Repair replied 1 year ago.

yes,,i understand,,it is possible that a quad driver is burnt out in the ecm ...

it is also possible that it is the pick-up..

again,we have ruled out the ignition module because you say you have tested and replaced it.

Customer: replied 1 year ago.
One last link, here is the link with absolutely dead ecm, and voltage at the injectors. He had no SES light, no codes, nothing, completely dead. Replaced ecm and all was fine. But note, he had voltage in run position, not crank, and voltage at the fusebox on inj a/b. It is also a just answer link, and on my specific 1988 3500, but he had the other headlight asy of the newer model of the 88 yr
http://my.justanswer.com/question/guest/77323e31996b464dae720570a93e33ab
Expert:  Tim's Auto Repair replied 1 year ago.

i understand this,,

but,i am addressing your problem on the info you are giving me

thanks

Customer: replied 1 year ago.
Please check the two links I sent you with just answer solutions that say the injectors should be hot in run not crank position, and the second which has a completely dead ecm with not a sign of life, no SES light, no codes, but still had voltage at the injectors, and note that both techs requested in the diagnostic to check for steady, 12vdc at the injectors, at run, not crank position. That, is what I cannot get past. ALL TECHS HAVE REQUESTED TO CHECK TO INSURE THAT THERE IS 12V AT THE INJECTORS WHILE IN RUN NOT CRANK POSITION.
Expert:  Tim's Auto Repair replied 1 year ago.

i really dont understand what you are trying to prove to me

Expert:  Tim's Auto Repair replied 1 year ago.

what are you wanting me to tell you?

Customer: replied 1 year ago.
That voltage to the injectors is not dependent on crank sensor or ecm, per Just answer links
Expert:  Tim's Auto Repair replied 1 year ago.

where does the voltage come from?

Expert:  Tim's Auto Repair replied 1 year ago.

all the wires to the injectors come from the computer,,the computer breaks the ground to create a pulse

Expert:  Tim's Auto Repair replied 1 year ago.

the computer uses inputs from the ignition module and the pick-up .

Expert:  Tim's Auto Repair replied 1 year ago.

the module and pick up tells the computer["i am turning,activate the injectors"

Expert:  Tim's Auto Repair replied 1 year ago.

if the pick-up and /or the module doesnt send the signal,or the computer doesnt know it is getting the signal that the engine is turning,the computer doesnt know it is turning and will not activate the injectors or the fuel pump..it wont give a code,because it doesnt know it is turning in the first place.

Customer: replied 1 year ago.
The fuse, I presume. Honestly, not disputing you, just going by what all of the techs have had others check, and all told them to check for this voltage. It could be possible that a completely dead ecm gave this voltage, but seems doubtful. Please, read the links I sent, do not take my word for it. These techs said the ecm grounds the injector circuit to fire the injector. Prior to this, the injectors are hot, and have an open, ungrounded circuit. Please read the 2 justanswer links to confirm this, please
Expert:  Tim's Auto Repair replied 1 year ago.

you are very correct,,it is possible that the computer is dead

Expert:  Tim's Auto Repair replied 1 year ago.

lol,we have established that .

Expert:  Tim's Auto Repair replied 1 year ago.

i gave you the diagrams so you can test all you need to test.

Expert:  Tim's Auto Repair replied 1 year ago.

these obd1 systems are fairly simple

Customer: replied 1 year ago.
I will get the coil tomorrow. Please at least read the second lnik, with an ecm so dead that it had no diagnostics, no light, no codes nothing, but he had the voltage to the injectors, that the justanswer tech told him to check for in run, not crank (and thus, would not need, any crank info, not cranking, no movement of the crank, no input from the pickup, and a completely dead ecm, and he had voltage that the tech predicted sshould be there)
Customer: replied 1 year ago.
I will let you know what I find tomorrow, but I am pretty certain that will make no diff. Will check this site before I get it, to see, after reading the second link, if you still feel this to be the culprit.
Thanks, ***** *****
Expert:  Tim's Auto Repair replied 1 year ago.

an ecm can malfunction in many different ways,,it is a computer,,it can go completely dead or only loose drivers to certain things,,this guys opinion/problem may or may not be relevant to your problem..my thoughts are the same..

either the pick-up or the ecm..if the wire harness is good

thanks

Customer: replied 1 year ago.
I looked at the schematic, and part 4/4 shows the voltage goes, "ign - 10a fuse - inj 1 red and inj 2 white - to d14, d15 and d16 in the ecm plug, which are listed as injector drivers. That, would lead me to suspect the ignition switch, assuming ign is the ignition switch, as the circuit stops being hot at the fuse. Anyway, going to bed, will get a pickup tomorrow, unless you say this seems logical tomorrow when I get up.
g'nite
Expert:  Tim's Auto Repair replied 1 year ago.

do you have power on the ecm1 and ecm2 with the ignition on?

Customer: replied 1 year ago.
where is the ecm1 and ecm2?
I have power to the ecm fuse, the ecm is doing self diagnostic, and returns code 12. Is ecm1 and 2 on the service port?
Also, I bought the pickup coil, not yet installed. Will be outside, but will check back from time to time
Thanks
Steve
Expert:  Tim's Auto Repair replied 1 year ago.

if you have power on the ecm fuse,it should have power to the ecm...

if the pick-up doesnt fix you,i would think you will need to replace the ecm

Customer: replied 1 year ago.
I found the problem. FYI, the ecm was a wild goose chase. After solving the problem, per a friend, I completely unplugged the ecm, and the engine ran surprisingly well, although I was told it was in limp mode. Thus, had I replaced the ecm, it would have been wasted money. The problem was a corroded fuse socket at the ecm fuse, and/or the injector fuse. It was on the secondary side of the fuse, such that a test light showed power to both sides of the fuse, but power was not passing to the secondary side of the fuse (s).
Customer: replied 1 year ago.
Honestly, I am not happy with the advice, though I realize you tried, and should be paid some for your work. Seemed that I was given shotgun diagnostics, with parts replacement by the odds of failure. The biggest concern though, is that the engine will run without the ecm even connected, so that was completely erroneous advice, and could have cost over a hundred, had it been followed. I did not elect to do the refund, but feel it would be fair to half the payment, due primarily to the faulty ecm advice and the fact that you seemed to ignore the fact that I should have had voltage to the injectors, and I actually determined the cause, indirectly when I mentioned that the circuit logic had nothing between the battery/ignition and the injector, except for the fuse. I though it might have been the ignition switch, but it was one step further down the line at the fuse.
Let me know if this offer of half payment seems fair, and if it is, will give 4 stars for effort any way. Going forward, please listen to your client, as we sometimes have pertinent info, rather than endlessly defending your recomendations, which in this case, were totally wrong, and would have been very costly to find this out.
Thanks for the effort anyway
Steve
Customer: replied 1 year ago.
Last chance, Tim, I do have an option, that is a total refund, if you do not reply to offer to pay half. Your shotgun method of replacing parts till it was fixed was not helpful. I could have swapped engines and had the same result, failure. The engine will run without the ecm, which you said would kill the injectors, You ignored the repeated statement from me that the that the injectors should be hot, and that nothing was between the battery and the injectors, except the ignition switch and the fuze. You insisted that the ecm could cause no voltage, in spite of schematics you sent saying otherwise. Half or nothing, your choice
Steve