Tbi no start with code 34

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Grand_Wag_85
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Tbi no start with code 34

Post by Grand_Wag_85 »

Trying to diagnose the no start condition in my J10. Getting a code 34, fuel is spraying but not firing. Any ideas?

I bought a new ignition module and spark tester and will be checking those later. I am thinking that I have a no spark condition but as I understand the tbi the ecm needs to see a spark to fire the injectors.
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derf
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Re: Tbi no start with code 34

Post by derf »

The TBI ECM needs to see the distributor signal. It doesn't necessarily need to see the spark. If the injectors are firing, the signal is getting from the distributor to the ECM. So you know the distributor is working, as is the ECM.

So if you have the computer controlling a GM HEI module, it could be between the computer and the module, the module is bad, or there's a problem between the module and the coil. If you're running a normal Motorcraft ignition system, either the signal isn't getting from the distributor to the ignition module, the ignition module is bad, or there's a problem getting from the module to the coil.

The cheapest thing to start with is checking all of the wires to make sure everything is connected the way it's supposed to be. If you have a spare ignition module, swapping it in will tell you if the one that's installed is bad.
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

7 pin module on large cap HEI on my setup
Last edited by Grand_Wag_85 on Tue Jul 26, 2016 11:57 am, edited 1 time in total.
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

7 pin module on large cap HEI on my set up.

Edit: not sure why that posted twice.
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Re: Tbi no start with code 34

Post by derf »

There are two sets of two wires going between the distributor and the ECU (usually bundled together). One carries the trigger signal from the distributor to the computer. The other set carries the coil trigger signal (once the computer determined delay has been added) from the ECU back to the module in the distributor. Check those second two wires end to end for continuity.

Check the module in the distributor. It's possible that it has gone bad and won't trigger the coil. A replacement ignition module isn't terribly expensive and is useful in a box of spare parts you keep in the truck.

Check the wires that go from the 7 pin module to the coil to ensure they're connected and working properly.

If all else fails, it's possible that the computer has a bad connection or is otherwise broken in some way. If you have a spare computer, give it a whirl.

I'd be surprised if the problem was anywhere but one of those places.
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

Thanks Roy. I'm gonna try my spare ecm and see whatwhat happens when I swap the module and look at the wiring.
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

Ignition module is fried. Hooked to a diagnostic test machine and it failed all tests.

Won't know until tomorrow if it runs, gotta replace the starter as well. The exploding battery had a LOT of collateral damage.
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Re: Tbi no start with code 34

Post by babywag »

code 34 is MAP sensor or wiring fault
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

babywag wrote:code 34 is MAP sensor or wiring fault
Exactly. WTH?
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Re: RE: Re: Tbi no start with code 34

Post by derf »

babywag wrote:code 34 is MAP sensor or wiring fault
That might also be a problem. It's worth looking at the sensor and checking the resistance while it's hooked to a vacuum gauge.
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Re: Tbi no start with code 34

Post by FSJ Guy »

Those GM ignition modules can test as bad even though they're good. <shrug>

The MAP sensor is one of the few sensors that the ECM needs in order to run the engine. With a bad MAP signal, idle is terrible and it won't run well.
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

Would a bad MAP (or wiring) sensor cause a no-start condition or just bad running?
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Re: Tbi no start with code 34

Post by FSJ Guy »

It could cause a no start.
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

New ignition module in place and it fired right up on the first crank. No longer throwing codes either. :-

I don't get it but I'll take it!

Will be testing the MAP tomorrow
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Re: Tbi no start with code 34

Post by derf »

Good to hear.

And BTW, here's how it's all hooked up inside the module:

Image
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Re: Tbi no start with code 34

Post by Grand_Wag_85 »

Thanks Roy!
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Re: Tbi no start with code 34

Post by tgreese »

derf wrote:Good to hear.

And BTW, here's how it's all hooked up inside the module:
<IMAGE>
Cool diagram. Where did that come from? Saved for future reference.

Interesting that advance is controlled by a duty cycle modulated square wave.
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