I switched the timing 180 and got no joy. I did realize that the injectors are not firing. The ign wires to the injectors are hot at ign and crank. I tested the continuity of the injector signal wires and it is good. The B wires on the injectors wont ground out so that they will squirt. Crank signal is good so that is not an issue. I made (with a schematic supplied by a guy who sells efi kits) a voltage spike filter that goes between the - coil terminal and the ECM. The voltage I got off of the - coil was 5-6V that varied as you cranked. Is there any thing else that if not present the ECM wont fire the injectors?

Ricko.

Main thing is if you are getting an engine speed signal from the distributor. If this is present, then your injectors should be firing. If you are not getting any fuel, check for fuel pressure, (min ~12 psi), a good ground on the TBI and for an engine speed signal. If you have all of these, she should at least be putting in fuel. From there it is just a spark thing.

(Assuming fuel pressure isn't a problem)

I had the same problem when I first fired up my TBI. The motor cranked but it wouldn't fire.

Turns out I had one wire hooked up wrong. There is one lead that needs to go to a "12V when cranking" source. In other words it's hot only when you're trying to start the motor. A normal switched power lead (12V when the truck is running) turns off during cranking. If you've got it hooked up wrong, the ECM thinks the key is turned off and it won't feed gas to the motor.

You can easily verify that this is the problem. If the injectors aren't feeding gas to the motor when starting, check to make sure the ECM is grounding the injectors. If it is, squirt a little gas in the throttle body. The motor should catch and run. Once it starts leave the key in the run position and the motor should run normally. If the motor won't start this way you've got other problems.

Ok, I have been searching for answers, and you look like you are in the middle of the same type of project.

What I have, 304 AMC V8, ESC conversion like your cruiser, chip burned for another same displacement AMC V8, 7747 ECM, 305 TBI, 1988 Astro Harness, single wire O2 sensor. New 16psi pump. Not guage to check fuel pressure.

Problems:

Open loop, great idle but backfires when you hit the throttle rapidly, and not as much power as the original MC 2100 carb.

Closed loop, if it does not die, it is all but undriveable.

I have NO dang clue what is not working. Any suggestions?

Ed

Originally posted by Rock Taxi
What I have, 304 AMC V8, ESC conversion like your cruiser, chip burned for another same displacement AMC V8, 7747 ECM, 305 TBI, 1988 Astro Harness, single wire O2 sensor. New 16psi pump. Not guage to check fuel pressure.

Problems:

Open loop, great idle but backfires when you hit the throttle rapidly, and not as much power as the original MC 2100 carb.

Closed loop, if it does not die, it is all but undriveable.

I have NO dang clue what is not working. Any suggestions?

Ed

Have you checked for codes?

Have you put the knock sensor in the 304? Are you using a 305 knock sensor or a different one?

I believe that the computer uses the knock sensor to help advance the timing. Without it the computer is lost and probably can't advance the timing enough to make the motor run right.

Originally posted by Rock Taxi
Ok, I have been searching for answers, and you look like you are in the middle of the same type of project.

What I have, 304 AMC V8, ESC conversion like your cruiser, chip burned for another same displacement AMC V8, 7747 ECM, 305 TBI, 1988 Astro Harness, single wire O2 sensor. New 16psi pump. Not guage to check fuel pressure.

Problems:

Open loop, great idle but backfires when you hit the throttle rapidly, and not as much power as the original MC 2100 carb.

Closed loop, if it does not die, it is all but undriveable.

I have NO dang clue what is not working. Any suggestions?

Ed

I had similiar problems when I installed a TBI on my 258,,, it was due to intake vacuum leaks....

OK, the Throttle Body I got had 4.3 injectors.

Replaced with 305 injectors and idles perfectly now.

Bogs and stumbles badly on acceleration. Seems like timing or fuel starvation.

Slapped the carb on and undid all the other mods to be ready to wheel.

Still want to do EFI, just need more info and time. Any suggestions on the bogging?

Ed

I had the same problem on a buddies jeep we built 2 winters ago.Had gotten a built 283 in on trade for some work he had done, just had to use it motor was built for a streetrod but never used. Got it running first had this real rumpty-rump cam swapped that out for one that he had gotten from his partsman, still a little big I believe. Then came the backfire thru the tbi, I tried plugs,wires,different tbi's, injectors and timing,fuel pressure setting and knock sensors. No luck, he tried to run it this way at a spring ride in monteagle wasn't happy when he got back. I had a holley tbi with the larger bores on it put that on and it is fine now with everything wired as gm wanted. I think it wasn't getting enough air to fuel ratio with the stock tbi, hence the rich mixture and backfiring. You might look into that. The thirdgen.org board may be some help also I had gotten some good help there on the problem with this jeep.

Originally posted by Rock Taxi
OK, the Throttle Body I got had 4.3 injectors.

Replaced with 305 injectors and idles perfectly now.

Bogs and stumbles badly on acceleration. Seems like timing or fuel starvation.

Slapped the carb on and undid all the other mods to be ready to wheel.

Still want to do EFI, just need more info and time. Any suggestions on the bogging?

Ed

If the ECM came from a 4.3 equipped vehicle then it's got the wrong Cal Pak in it for your application. GM can sell you a Cal Pak for a 305 equipped vehicle. The Cal Pak tells the ECM how much fuel to feed the motor (and other things). If you've got a 4.3 Cal Pak in there it will starve a 304. There is a small cover plate on the computer (held on by two screws). Remove it and you'll see a small removeable chip. Ask GM for a Cal Pak from a TBI 305 equipped vehicle (like a 1/2 ton pickup). Pop the old Cal Pak out and put the new one in.

If the knock sensor is from a 4.3 you'll need to get one from a 305. That may cure the any timing problems you've got.

The ECM was for a c1500 305, with an old Howell PROM chip from another person's 304 Howell installation. Is the CalPak just a new PROM or is it both chips? It is possible the ECM is a 4.3 and just mislabled. I did not uninstall it myself.

I have no knock sensor, and am suspecting that the knock sensor was not disabled on the Howell PROM. I am hearing running without one supposedly retards the timing and make is run like crap too. Could be my issue.

305 vs 4.3 knock sensor huh? Can do. I'll try that when I get back from the trip this week.

Ed

Originally posted by Rock Taxi
The ECM was for a c1500 305, with an old Howell PROM chip from another person's 304 Howell installation. Is the CalPak just a new PROM or is it both chips? It is possible the ECM is a 4.3 and just mislabled. I did not uninstall it myself.


The 4.3 ECM and the 305 ECM should be the same. The Cal Pak (or PROM) is what makes the difference. Sounds like you've got that covered.


I have no knock sensor, and am suspecting that the knock sensor was not disabled on the Howell PROM. I am hearing running without one supposedly retards the timing and make is run like crap too. Could be my issue.

305 vs 4.3 knock sensor huh? Can do. I'll try that when I get back from the trip this week.


You heard correctly. The computer advances the timing until the knock sensor hears something then it backs off. The wrong knock sensor (or a missing one) will prevent the computer from advancing the timing properly. No advance = a motor that won't rev :D

Hope that's it.