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Old 10-03-2010, 06:44 PM
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TBI still does not stsrt...

So, I have installed a complete TBI system from an '88 Chevy half-ton (except the throttle body itself, from an Astro van because the injectors have a better size) on a 250ci inline 6 Chevy engine. The engine ran before the mods. I had to modify the distributor to work with the ECM (removed the weights and the advance system, connected an 8-pin ignition module).
The engine does not start: the starter spins quite nicely, I have no spark and no pulse at the injectors (they do have ignition +, just no pulse).
Following advice from this forum and ideas from the shop manual, I have checked everything:
I have continuity on all the wires, all the grounds are good, TPS, IAC and MAP are good, coil and pick-up coil are good, the ignition module was checked today at the parts store; coil, cap, plugs and plug wires are new. I have gone through all the wiring (I think...), everything is where it is supposed to be. I have tried 2 different ECMs. The O2 sensor is not connected because there is no exhaust pipe yet. I have no trouble code because this combo has never run.
So what now??? What is happening, what do I have to look at? What am I forgetting?
Thanks!

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Last edited by wave1957; 10-03-2010 at 06:49 PM.
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Old 10-03-2010, 07:24 PM
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The ignition module wiring is incorrect for the system.You have an 8 pin from a coil in cap system and the pins and connections are different from the external coil type like the system you have uses
I am not sure they are compatible but if someone has one and it works I suspect the module wiring is wrong.Answer me these 2 questions!
Did you use the module pictured on the jeep website coil in cap distributor? and does the original module from the 88 truck system have external coil setup?
If so I see 2 wires that are reversed and all 4 may be.I cant find enough definitive info on pin function. But I think at least 2 pins are reversed.Maybe all 4.
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Old 10-03-2010, 08:23 PM
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"Did you use the module pictured on the jeep website coil in cap distributor? and does the original module from the 88 truck system have external coil setup?"

Well, Latech, thanks for your time, it is a shame you are not in Calgary!!
Anyway, I do not use the same module as pictured on the Jeep forum, this is an in-cap, 7-pin module.
I use the 8-pin module that was on the '88 truck, that way, the harness fits the module: I thought it would be easier to keep as many parts as possible from one donor vehicle only. That '88 truck had a small cap HEI with external coil.
http://www.megamanual.com/ms2/GM_7pinHEI.htm
This site, although it deals with a Megasquirt computer system, does explain well what connector/wire is what. My module is at the bottom left of the opening picture. 7 and 8 pin modules are described separately, further down the page.
Hope it helps...

Last edited by wave1957; 10-03-2010 at 08:33 PM.
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Old 10-03-2010, 08:27 PM
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That baby should be running .I am gonna have to scratch my head... again... for a while...
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Old 10-03-2010, 08:30 PM
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how about the distributor? Is the plate grounded to the distributor?maybe you are missing the ground connection for the module?
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Old 10-03-2010, 08:35 PM
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Either that or the pickup coil is not generating. seems to me you checked polarity on that.did you check signal (output) voltage.How about an ohm reading?
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Old 10-03-2010, 08:36 PM
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I have checked that, the module is grounded.
I would think it should run too, but...
I am starting to think about this in my sleep, and I do not like it! And I am out of ideas...
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Old 10-03-2010, 08:41 PM
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All the ecu really cae about is a positive pulse from the module. If you get a multimeter and have a buddy crank the engine you should see this fluctuate. If it does not then the circuit is not complete for operation. No ground or the actuall connectors are plugged in incorectly to your tbi. The only way to try and make it compatible is to do a diode test on the module to find out which way the current travels in the circuit, so you can detirmine the proper wiring.
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Old 10-04-2010, 06:40 PM
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Quote:
Originally Posted by latech
Either that or the pickup coil is not generating. seems to me you checked polarity on that.did you check signal (output) voltage.How about an ohm reading?
Well, I was just in the garage checking that and the results look funny to me...
I had checked the pick-up coil as per the shop manual before and found numbers within specs. Today, the numbers make no sense at all. And the numbers vary depending I test at the module connector or directly on the small wires coming from the pick-up coil itself!
Testing the resistance of the pick-up coil, I find 0.01 to 0.04 at the module connector and about 5.73 at the pick-up coil itself;
Testing for continuity, I get about 25.5 at the module connector and 7 to 9 at the pick-up coil itself.
All this does not make sense, it would seem the wiring (I had to extend these wires to reach the module) cause a problem, otherwise, I do not understand what I am seeing here. And I had good numbers before...
Five minutes later, I went back to the garage and tried again, I guet similar results, with quite unstable numbers...
So, what do you think? And please, if I am the problem, tell me nicely, would you?
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Old 10-04-2010, 07:32 PM
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well, you cant test the pickup coil for anything if it is plugged in to the coil.
It has to be unhooked from the module to test for resistance,and voltage.
I think all the other tests you did (probing the module circuitry or components plugged into) are just wasted time. You cant test the module, nor should you wiith an ohmeter. If you extended the wires to the distributor take a real good look at them at both ends to make sure they are not crossed somewhere.check the connections also. Did you use butt connectors? I hate butt connectors. I perform a linemans twist on wire repair and then I solder it. Then I slide the shrink wrap into place(put it on before the twist of course)and shrink. Voila it wont pull it apart.
unplug the pickup coil again and probe the green and white with the ohmeter .It should be between 500 and 1500 ohms. That is a little wide for a spec but that what it is straight from the book.
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Old 10-04-2010, 08:27 PM
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The pick up coil was unhooked from the module to test, I did the tests with the distributor cap removed.
The module was tested at the parts store.
And I do all my connections the same way as you, twist, solder and heat-shrink. The wires coming from the pick-up coil has a double spade connector, so that is what I have used there, because I do not like to cut wires. The insulation on these 2 green and white wires is quite "cooked" and brittle, but there is nothing I can do about it, to change these wires would mean to change the pick-up coil...
I will re-check the pick-up wiring extension and try measuring it again... The shop manual gives the same specs you have. Tomorrow, I guess...
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Old 10-04-2010, 10:57 PM
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how to test module.
First find out which wires are positive and negative. Have the ignition key on and go with the negative probe on your multimeter to (-) negative terminal on battery. Then of course go to the positive lead on the module with your red or positive probe from multimeter. Check for a voltage reading

If all good secondly try
Continuity test from (-) negative lead to ground.

If all good thirdly try
Have a buddy or who ever crank the sucker and check for a pulsing voltage from the pick up coil. If there is voltage fluctuating then you got problems after the module. If there is not fluctuation while you guys are cranking engine then you got a bad pick up coil or module.

If all good thirdly try
Check to see if your injectors are working.

If all good STILL
You have a 12v turning off on you. To be more clearly, hood up a 12v directly from the battery positive terminal to your 12v input to the module.

If still after this no start
Then shoot it! Just kidding. Look to see if your TBI does not operate with a knock sensor. I did one of these conversions with a buddy and his had the 12v only staying on when you crank it and turned off as soon as you stopped cranking it. Then he forgot all about the knock sensor.

Last edited by 355Nova; 10-04-2010 at 11:03 PM.
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Old 10-05-2010, 12:41 AM
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Just to try and jog something here... I know with GM late model ignition systems, the crank sensor is a main input for spark. The ECU will never trigger spark or fuel unless it actually sees the engine cranking via the crank signal to the ECU. I'd say if all else is checking out, check to make sure that is still functioning properly. No crank signal = no fuel and no spark. Good luck!
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Old 10-05-2010, 04:12 PM
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Quote:
Originally Posted by Caballerokid
Just to try and jog something here... I know with GM late model ignition systems, the crank sensor is a main input for spark. The ECU will never trigger spark or fuel unless it actually sees the engine cranking via the crank signal to the ECU. I'd say if all else is checking out, check to make sure that is still functioning properly. No crank signal = no fuel and no spark. Good luck!

Where is the crank sensor on an 88 chevy half ton with TBI? (that is the system he is trying to run here!)
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Old 10-05-2010, 04:16 PM
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[QUOTE=wave1957]The pick up coil was unhooked from the module to test, I did the tests with the distributor cap removed.
The module was tested at the parts store.
And I do all my connections the same way as you, twist, solder and heat-shrink. The wires coming from the pick-up coil has a double spade connector, so that is what I have used there, because I do not like to cut wires. The insulation on these 2 green and white wires is quite "cooked" and brittle, but there is nothing I can do about it, to change these wires would mean to change the pick-up coil...


starting to sound like the pickup coil is the problem . what was the reading when you checked it?
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