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  #1  
Old 10-23-2006, 12:04 PM
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GM TBI Conversion Troubleshooting

Does anyone have a good source (web, preferably) for troubleshooting/diagnostics for a GM TBI setup? Mine is all in and wired, but refuses to fire up.

What I've checked so far:
  • Checked/double-checked/triple-checked wiring and vacuum, although the wiring diagram I have kind of sucks, so there may still be an issue or two I need to look into.
  • The pump is pumping and there is fuel getting to the injectors (and on the throttle blades.
  • According to my fancy multimeter the coil is getting the signal to spark (haven't actually checked that there is spark at the plug or the timing).
  • The engine cranks fine and the battery is charged.
One thing I am especially unsure of is the initial timing? Does it need to be set at 0, 5 or 10-degrees? If there's anything else I might have overlooked, let me know. If you can point me in a direction where I can read up on troubleshooting and/or common pitfalls of the install, that would be great too.
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  #2  
Old 10-23-2006, 12:21 PM
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I have a few links here:

http://www.grimmjeeper.com/tbi/



Are you sure you have your distributor correct? A lot of people put it in 180* off. I know I've done that my share of times or more.

Have someone crank the engine to see that you're getting full spray out of the injectors.

Run a timing light and make sure your timing is somewhere close.

If you're doing computer controlled spark, you want to set the timing to 0 degrees. If you're doing regular vacuum/mechanical advance, you need to set it to whatever the default timing is for your 79.
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  #3  
Old 10-23-2006, 12:34 PM
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a couple of things to check.

1. you said it's charged. Make sure that while cranking, you have consistent 12v. Otherwise, it won't fire.

2. check the injectors. Pull all of the injector wires and set them aside, and disconnect the battery. Then, using a positive and negative lead from the battery (10ga wire works), put a positive and negative to each of the injector terminals, one at a time. If they click, they are open and should spray fine. I found that 6 of my 8 were frozen. If yours end up not clicking, disconnect the leads you attached to the battery and use a hammer and a long socket wrench extension and set it against the injector body. Tap the hammer against the extension for about 15-20 hits, then test again. I had to hit some of mine like I was driving 16 penny nails through pressure treated lumber, about 60 times before some of them opened up.
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Old 10-23-2006, 12:35 PM
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Thanks, I'll take a read through that stuff.

I'm pretty sure I have the distributor in correctly. I did have to pull it out to lock the mechanical and vacuum advance down, but I marked it before I pulled it (wasn't on #1, but doesn't really have to be). When I put in back in, it lined back up to my mark and engaged the oil pump just fine, so I'm reasonably confident it's in there right. I had it set to 12-degrees BTDC (for the carb) when I pulled it so I guess I need to back that off since I am doing the computer controlled spark. The only other thing I can think of that might have gotten messed up with the distributor is the toothed pickup wheel. I had to take that off and put it back on. There are two positions it can go on and even though I'm pretty sure it's on the same way it came off, there's a small chance it could be indexed incorrectly (I'm not sure how much difference there is if it is incorrect).

I'll make sure to check the injectors and set the timing tonight before I give it another try.

Thanks!
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  #5  
Old 10-23-2006, 12:40 PM
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Quote:
Originally Posted by billyrb
a couple of things to check.

1. you said it's charged. Make sure that while cranking, you have consistent 12v. Otherwise, it won't fire.

Most batteries I've ever seen drop to ~9-10V during cranking. It is a fairly new battery and I had it on a charger for almost the entire day (charger said 100% charge when I took it off and it was sitting at 12.88V according to my DMM).

Quote:
Originally Posted by billyrb
2. check the injectors. snip...
Definitely will do! That's crazy!
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  #6  
Old 10-23-2006, 12:46 PM
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I think Ryan is trying to say that you should have voltage available to the system during starting, not just @ Key on.
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  #7  
Old 10-23-2006, 12:53 PM
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wouldn't hurt to start the engine on carb cleaner, then you can narrow things down a little (spark/timing or fuel delivery)

pics! (when it's done of course)

peace
Dave
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  #8  
Old 10-23-2006, 12:53 PM
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Okay... That makes sense. I'm fairly certain I do, but like I said, the wiring diagrams I had to work with were somewhat lacking. I'll be sure to check that too.
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  #9  
Old 10-23-2006, 12:58 PM
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I would check to see if the spark plugs are sparking to rule out the coil. If not, I would check to see if the starter solenoid wire is placed on the correct terminal (tells the computer that you are starting the vehicle) and has a good connection. If it is on the wrong terminal you will get symptoms like you mentioned.

Did you set the timing with the one wire coming off of the dizzy disconnected- I believe it usually has a connector on it you can disconnect for timing? I also would check for vaccuum leaks/uncapped ports in the front of the TBI.
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  #10  
Old 10-23-2006, 01:01 PM
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Quote:
Originally Posted by Valdez Explorer
I think Ryan is trying to say that you should have voltage available to the system during starting, not just @ Key on.

yes, we swapped a 4.3 into a tj, and the guy who wired it hooked up the wires to the wrong pos on the ignition... when the key was turned to start, the power was taken away from the computer circuit. (like how your radio shuts off when you crank the engine)
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  #11  
Old 10-23-2006, 01:11 PM
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That's sounding more and more like it could be the problem. It seems like it should at least pop even at 12-degrees advance. Now to figure out which wire is connected incorrectly...
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  #12  
Old 10-23-2006, 07:00 PM
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http://www.binderbulletin.org/forums...splay.php?f=75
This is a great site with a wealth of knowledge.Also very nice people
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  #13  
Old 10-23-2006, 08:36 PM
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Big Red, I have the print out from Affordable Fuel Injection TBI if you need to read it.
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  #14  
Old 10-23-2006, 11:33 PM
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Well... I went hunting for a wire I couldn't find in the part of the loom in the engine bay and sure enough the crank signal wire was hiding about 6" from the connector at the computer. I also found out the 02 sensor wire went into the cab-side of the loom, but never connected to the computer. The rest was fine, so now the wiring has been checked from computer to component.

The injectors spray during cranking.

The computer, coil (a relatively new TFI type) and everything else that needs it have power with the ignition in the run and start positions.

All unnecessary vacuum connections are capped.

What else can/should I check? Timing is going to be difficult since my crank bolt won't take much torque before it strips again. It's barely hanging on as it is.
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  #15  
Old 10-24-2006, 01:51 PM
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If you look at the link I posted in the faq there is a great deal of info.Also if all else fails Bill from that forum can be a great help
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Old 10-24-2006, 02:01 PM
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Check that you're actually getting spark. You can pull the #1 spark plug wire and stick a key in it. Hold it next to, but not touching the block. DON'T TOUCH ANY PART OF THE VEHICLE WITH ANY PART OF YOUR BODY. Have someone crank the engine. You should see and hear the spark between the key and the block.
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  #17  
Old 10-24-2006, 02:28 PM
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LaJ10 - I must have missed that link. I'll head over there and take a look around. Thanks!

derf - I've got an inductive timing light so I might see if that shows spark before I try the key or screwdriver trick.

These systems are so simple I'm a little surprised it is being this difficult to get running. It's not like you have to time injection like you would with MPEFI, so as long as the spark is reasonably close to TDC and fuel is getting there it ought to run, even if it runs badly.
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  #18  
Old 10-24-2006, 03:46 PM
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Another trick for checking spark is to pull the wire and put an old plug in it. Vice grip it (the plug) to something metallic on the engine. Crank the engine and watch for spark. This way you don't need to worry about getting shocked

Are you using a HEI module to run the TFI setup?
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  #19  
Old 10-24-2006, 04:26 PM
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My dad was just suggesting the same type of thing for testing spark...

Yes, I am using an HEI module to run the TFI coil. Are there any diagnostics specifically for those modules?
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  #20  
Old 10-24-2006, 06:38 PM
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Are you running the 7 pin or 8 pin module?Autozone and some other parts stores can test 8 pins not sure about the 7 pin tho.Have you done any key on voltage checks?What ecm are you running?If it is a 1227747 this is the pinout and voltages.Which coil are you using?I would first check for spark if you do have spark at the plug then I would pour a little gas down it and see if it does anything.If it still does nothing then check again and make sure it is a tdc compression stroke #1.You can do this by taking out the #1 plug and have someone bump it over until the #1 cylinder blows air out.Once it does that look fore the timing mark and rotate the engine backwards to it and check the distributor.Make sure the rotor is pointing dead at the #1 plug on the dist.cap.If you are getting fuel and spark then it should run.
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