Chevy 350 Throttle Body Problem

[Pinkston]

I have an odd ball set up, but I figured this would be the best place to ask. In my isuzu trooper I have a 4.5 V8 out of a 1990 cadillac deville. The motor has a chevy 350 throttle body on it with a chevy caprice 350 computer running everything. The trooper came with a GM 2.8, so the wiring harness did not need much modification to make this motor work.

The motor has been in and running for over 6 months with zero problems until last night. I was pulling out of the drive way and it cuts off all of a sudden. Now it wont start back up. After looking at some things I found that it is getting spark, it is getting fuel into the throttle body, but fuel is not getting past the injectors. I am 95% sure the injectors are not the problem. I had a spare injecor that I put in and it still has the same problem. I also tried a spare computer and had no luck. I know the fuel pump is working and getting fuel to the throttle body.

Its an oddball set up, but does anyone have any suggestions?

 

[91yota]

sounds like the signal to fire the injectors isnt getting through... maybe check continuity on the wires going to the injectors and see if they are good... are you sure your spare computer is good??? not likely but both computers could be bad- although i dont think that is your problem... my first bet is the harness going to the injectors... also check the connectors themselves to make sure no pins have backed out.... keep us updated

 

[Yay!Gurrr]

id start with your trouble codes (paper clip in aldl connector) Have you checked the fuses ? There can be fuses for each enjector in addition to the ecm. etc..

Thanks for mentioning the harness stuff... So you simply swap the ecm and the larger TBI onto the existing harness ? On the bigger engines they usually run two leads, one to fire each injectors to supply enough current. Smaller engines can use one. Possibly you original 2.8 harness had one and it was overloaded.

Whats the numbers on your ECM?

Check your grounds usually the biggest issue is your junk doenst get grounded and wont work right... make sure your engine is grounded to the body and your battary ground is to the engine and is good...

 

[wbcarver]

I have an odd ball set up, but I figured this would be the best place to ask.

Heyyy whachew trying to say?!?!?
We're oddballs around here ?!?!?







OK - serious now.

Going to assume, you don't have 2 bad computors.

First - beg borrow or (gasp) buy a set of "Noid Lights"

See if there is pulse to the injectors.

Yes or no.

Probably NO.
If no and you are pretty sure there is fuel pressure TO the injectors.
Then - unless you have a connection somewhere that has come loose,
(not exactly sure of your set-up) are you running a distributor or a coil pack?
Most likely problem is going to be
Either crank sensor or pick-up coil. I forget which ones used the pick-up coil for injector pulse. Chances are if you have spark it is not the pickup nor the module.
Also not sure what years but I think there is a cam sensor in there too?
Might be the culprit.


Just thought of something else. If you can't get your hands on a set of noid lights, you can put a timing light on it and shine the light down the throttle bore while cranking. The strobe will let you see the fuel pulse if ther is actually fuel coming out - sometimes you just can't see the fine spray.

If you don't have any spray you are still back to the noid lights, but it is a start.

 

[91yota]

something else to think about... some advice from another board i go to and posted your ? on:

First thing is to check for fire at the injectors. With the key switched “onâ€, one side (one wire) on each injector should be hot (12v)……I think it’s the pink wire(s). The other side (other wire) is the ground wire but this ground comes from the ECM. The fire is always there (or should be) when the key is switched on, the ECM is what fires the injectors by grounding it…..repeatedly…..really fast…….to pulse it. If there is not a “hot wire†then that problem needs to be found. If there is a “hot wire†you need to check for the pulsating ground. If this isn’t found, there is either a bad ECM or a bad ignition module.

 

[Lee]

I looked at pinkston rig for awhile this evening, there is 12volts getting to the injectors, the problems is they are not getting the ground pulse from the computer.

All the wiring ohmed out perfect with no shorts to ground anywhere.
tried 2 different computers with no luck?

A bad ignition module would cause no fire also though?

looked at some stuff and found this: http://chevythunder.com/fuel injection troubleshooting page C.htm

Disconnect on of the injectors from the harness, and with a injector tester lamp (noid lamp), or a test lamp that one end is connected to a hot (12V), probe the green/blk or blue/black wire and with the engine cranking, the lamp should blink. If it blinking, the problem lies in the fuel delivery system, that will be discussed a little later. If the light is steady, the problem is in the injector drive circuits, the green/blk or blue/black wires that are shorted somewhere to ground. You'll have to pull the terminal to the ecm and with all the injectors disconnected, hook up your continuity tester to ground and probe these wires, the light should not come on. If it does, find and repair the shorted wires. If the lamp does not come on, check the resistance of each injector, with your ohmmeter, the resistance should be more than 10 ohms( typically around 15-16 ohms). If the injectors check out okay, the ecm is faulty. If the not okay, replace the any injectors that measure less than 15 ohms. Now, if you don't have a blinking light, plug in the injectors back in, then you'll need to turn the ignition key on and probe the injector harness terminals to ground with your test lamp, the light should be on at both terminals, this is due to the fact the injectors are wired in parallel. If there is not a light at both terminals, the problem is in the injector harness. If the light comes on one wire, the problem is in the harness to the injectors.

Now, if the light comes on in both terminals, reconnect your test light to injector harness, and disconnect the 4 way distributor connector. Momentarily touch the connector with the purple/white wire with a test light hooked to 12V, if the injector light blinks the problem is a bad ignition module. If there is no blinking light, disconnect the tps and repeat the test. If the light blinks, replace tps. No blinking light means you'll need to make sure the fuel pump runs for its two second priming period. If the fuel pump checks out okay, reconnect all your injectors, turn the ignition off, disconnect your ecm, turn the ignition key back on, and probe terminal D15 with the test light connected to a hot power source, if the light comes on, you'll need to wires to injectors (green/blk or blue/black) being shorted to a voltage source. If they are okay, the ecm is at fault

 

[Yay!Gurrr]

just checking what you measured.... you ohmed the injectors at the ecm plug ?

the pics are for my ECM so disreguard the specifcs but the concept is the same... per the ECM pin out paper you should see +12 on each leg when tested "AT" the ECM connector.

 

[Pinkston]

Thanks for the replys and tips. We got it running on friday. Everything checked out back to the ecm so we thought the ecm might be bad. Had the ecm checked and it was good so we moved on to the ignition module. While replacing the ignition module we found the problem. The clip on the conector for the wiring to the ingnition module broke disconecting the wires. Basically the ignition module was not able to give a signal to the computer so the computer was not supplying a ground for the injectors.