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Discussion Starter #1 (Edited)
Been a member for a while but haven't posted much...I've been doing the mother of all rebuilds. Sorry for no posts but I took lots of pics and will post extensively.

Sadly par for the course? Major issues at new motor fire attempt.

89 gmc 4x4 2500 sub. 91 replacement motor rebuilt and new cam. Used all original electronics and tbi. New wires, plugs, cap, rotor, fuel filter,etc...
have spark, have fuel at the back of the tbi. No pulse at all from either injector? This thing ran when I parked it to work on it. Checked fuses inside @ fuse inside...don't have the money to just start buyingc electronics until it works. Wondering if anyone has an idea? Already read several accounts online but all had no spark or no fuel or tried changing things from factory. Mine is 100% original and worked when parked? WTF?

---------- Post added at 03:30 PM ---------- Previous post was at 01:53 PM ----------

I pulled the four pin connector from the dist. all I have is a standard radioshack volt meter. Purple/white wire with key on had barely any signal at all. Wires to the injectors have 12v with key on. I have fuel at the rear of the tbi but not sure of the pressure? No pulse whatsoever.

---------- Post added at 05:09 PM ---------- Previous post was at 03:30 PM ----------

I am left to assume the fuel pump which I can hear run and never had an issue with before...now has not enough pressure for no reason at all? Or an electrical part failed while not being used? Both are perfectly reasonable? Right?
 

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Okay ecm fires injectors with ground...should have a set of ground wires at thermostat..and one on intake behind where ac pump is or should be.
Make sure clean and connected tight. Two other things work with firing injectors ..pickup coil..and ignition module.
Make sure you did not miss something a wire loose connection when you put all back.
Can you prime it will run for a few seconds?
 

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Discussion Starter #3
i have a major ground wire from intake to the firewall by the ac/heater box. It is good. As it is a brand new engine? I didnt want to pour gas in and temp fire it. It needs a break in
Id like to test the ignition module. Can I do it with a simple volt/ohm meter? Thanks for the help.
 

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If you can find a diagram for the ign module that shows what "good" ohm between pins on the plug would be you can check it vs what you're actually reading. Im not too keen on TBI injection systems personally... but do you know where exactly your injector pulse is supposed to come from?
 

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I guess no one reads....injector pulse comes from ecm..via ignition module..pickup coil.Once ecm senses 400 rpm,s from engine it takes over.
But injectors pulse works off of ground from ecm...you have to have the grounds at thermostat and intake or will not pulse injectors.Grounds for all sensors.
Can not test ign.module with a meter..due to heat variances .
Can take to auto parts to test. Have a machine that heats it up to certain temp.
Now you can ohm out the pickup coil on dist. shaft....disconnect green &yellow wire from ign. module
Set meter to ohm,s probe green wire with one lead from meter yel. with other ..should get 700 to 1200 ohm,s of resistance.
 

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Discussion Starter #6
Wow...not sure about the ground wires near the thermostat being that repainted it all. Could be poorly grounded. Will check in the morning. Thanks. That makes more sense than anything else.
 

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Discussion Starter #7 (Edited)
Sadly...all grounds are excellent. Have pressure. Module tested out fine. Battery grounded directly to motor. Unplugged tps and nothing. Repeated with all sensors. No pulse at all. Again...12v at each pod. All wires look fine.
 

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If it ran before ..you must be missing something..wire a connection..has to be either a bad ground..ign. module. pickup coil ..bad or clogged injectors
Or bad ecm.
 

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Discussion Starter #10
Bad module? Tested out fine.
Bad coil pick up? With spark?
bad ecm? With spark, 12v to each pod, 12v to coil? If with all these factors the ecm could be bad? If so I would like to know if the ecm controls none of these.
With fuel pressure, 12v to each pod, 12v to coil, good ignition module, spark seen on a timing light, motor grounded to block, two good and checked grounds...can the ecm be bad with virtually everything working seeking flawlessly? Both injectors suddenly clogged or died simultaneously while sitting on the garage floor?
 

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Discussion Starter #11
"Whenever you have eliminated the impossible, whatever remains, however improbable, must be the truth "

After pulling the dizzy and rechecking all wires, grounds and connections? And rechecking fuel and 12v at pods? I pulled apart the tbi...OMFG! what disaster. A rusted corroded wreck confronted me. This was NEVER in the weather and in my garage the entire time. It is so far gone I will have replace it. I'll also be pulling the tank and flushing it plus change pump for S and G's. I should have expected this...it has been like this on every inch of this project.

I'll post pics as soon as I can figure out how. Thanks for everyone's input. Much appreciated.
 

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Well maybe you found the problem..was going to tell you to disconnect tps ..ecm cut ground .flood mode.
Also check injector ground for continuity.
 

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Discussion Starter #13
No maybe about it. It is so rusted and corroded its unreal. I couldn't have left it in a fish tank this whole time and had less rust.
 

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Discussion Starter #15
Got the tank out...pristine inside. Putting in the new fuel pump tomorrow tomorrow as long as it comes in in time.
 

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did you check the pressure before you pulled the tank? There's no need to change the pump if you have 14lbs (unless you just want to change for peace of mind while tank's out).
 

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Discussion Starter #17
Okay im back after getting my 74 Monte carlo all done and ready to sell.

Changed out tbi. New fuel pump. Changed icm. Truck fired and waited to get exhaust done so the headers feed the o2 sensor.

Unplugged timing wire and correctly timed it to zero at idle. It starts but not easily. It idles very low like 400. Its rich and it randomly cycles at idle and at the low point it lights the check engine light.


Love to know what the hell before I rip it all out and use a Carb and hei.
 

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Discussion Starter #18
Site locks up if I try to edit...after reading up on this issue I replaced the tps with another I had. Same results. Wasn't able to read any voltage whatsoever out of the three wires going to it. So tps isn't it. Now what? Buy more new parts till it stops? Seems to be the most prevalent answers on most sites.
 

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Well got it running good . What do you mean no voltage at tps? You have a check engine light scan now . Jumper terminal a&b at adl port.With key turned to on.Watch check light will flash 1 time the a short pause 2 time ..be a 12 ready to go . then it will flash any codes stored.. 3 then pause 2 means 32 example.
Sounds like a 02 sensor. Will act like this light on then off. Should have a 5 volt reference at tps with key on...at gray wire i think.
Should get around .65 volts at closed throttle 4.50 volts at wot. Should have 5 volts at all sensor with key on.
 

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Discussion Starter #20
I turned the key on and tried to get a reading for voltage at the tps. I wasn't able to get a reading at all? I don't know what terminal a&b is to do a jumper wire? The o2 sensor
 
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