It's a riddle

Hybrid · 04-17-2007, 09:32 PM

Hey guys for those of you who know me, this is Jacob and I still have a tbi problem!! I can't get this 350 to run right. I have installed a tbi system with a brand new wiring harness, and i couldn't get it to run right so i started replacing things, like knock sensor, coil inside the distributor, and the harmonic balancer. When i pull the ground on the computer to set the timing to zero while on TDC it is really really hard to get it to zero without it stalling. Then when i get it pretty close i reconnect the ground and fire it back up. It will run really nice for a little while, but when it warms up the rpm's drop gradually until it eventually stalls. Oh and I have also checked the ECM and it works great when hooked up to another rig. If you guys have an answer to this riddle please let me know. Thanks

94Dodge Truggy · 04-17-2007, 10:38 PM

Does it have an oxygen sensor and are all of the wires to it ok? I gave up on my wiring gremlin and had it professionaly rewired as simply and cleanly as possible by JN electric. I have yet to get it back and try her out though.

Hybrid · 04-18-2007, 01:20 PM

The O2 sensor is brand new. I know the system runs in a closed loop until it gets warm, then it runs on an open loop. So I would think that since it runs pretty well until it warms up, that would suggest that something, maybe a sensor, is sending a bad message or maybe no message at all as soon as the loop opens. That is why I starting replacing sensors, but nothing has worked yet. Although when I replaced the knock sensor it run a whole lot better during that cold time.

mckeddie · 04-18-2007, 07:06 PM

is your oxygen sensor in the right place? i know it sounds dumb, but we've solved a few by measuring the distance from manifold, to make sure it is the proper distance, and getting the correct reading. this has worked a couple of for 5.0l's that we've worked with.

greg

Hybrid · 04-18-2007, 10:06 PM

I will measure the distance of the O2 sensor from the manifold and let you guys know. What would be the correct distance for a 350 with headers?

Mike F · 04-25-2007, 05:17 PM

GM TBI and most all OEM EFI systems run in open loop until the oxygen sensor warms up then goes into closed loop. The older GM truck TBI usually idles in open loop even after being warmed up.

Sounds like it could be a bad temperature sensor or IAC, hard to tell. The oxygen sensor should not effect idle. The sensor on a header needs to be placed in the collector near the flang in order to see all the cylinders. The problem is if it will heat up to 500* in order to read correctly, you may need to install a heated 3 wire oxy sensor so it gets up to 500* or more. The old GM TBI computer is to slow to worry about the slight amount of time it takes the exhaust gas to get to the oxy sensor mounted out on the collector. I have a buddy with a one wire one that we put in the collector and I know it works in the summer but I do not know about the winter time, it runs OK in the winter so I have never hooked to it then.

GM TBI is a pretty simple system but it would be nice to hook into it to see what the problem is.

04-17-2007, 09:32 PM	#1
Hybrid Join Date: Mar 2007 Location: Fairfield, OH Posts: 134	It's a riddle Hey guys for those of you who know me, this is Jacob and I still have a tbi problem!! I can't get this 350 to run right. I have installed a tbi system with a brand new wiring harness, and i couldn't get it to run right so i started replacing things, like knock sensor, coil inside the distributor, and the harmonic balancer. When i pull the ground on the computer to set the timing to zero while on TDC it is really really hard to get it to zero without it stalling. Then when i get it pretty close i reconnect the ground and fire it back up. It will run really nice for a little while, but when it warms up the rpm's drop gradually until it eventually stalls. Oh and I have also checked the ECM and it works great when hooked up to another rig. If you guys have an answer to this riddle please let me know. Thanks

04-18-2007, 07:06 PM	#4
mckeddie Join Date: Apr 2007 Location: van wert oh Posts: 583	is your oxygen sensor in the right place? i know it sounds dumb, but we've solved a few by measuring the distance from manifold, to make sure it is the proper distance, and getting the correct reading. this has worked a couple of for 5.0l's that we've worked with. greg __________________ zuk buggy.....it'll be a jeep eventually.

04-25-2007, 05:17 PM	#6
Mike F EFI AMC 360 Join Date: Mar 2007 Location: New Lebanon, OH Posts: 32	GM TBI and most all OEM EFI systems run in open loop until the oxygen sensor warms up then goes into closed loop. The older GM truck TBI usually idles in open loop even after being warmed up. Sounds like it could be a bad temperature sensor or IAC, hard to tell. The oxygen sensor should not effect idle. The sensor on a header needs to be placed in the collector near the flang in order to see all the cylinders. The problem is if it will heat up to 500* in order to read correctly, you may need to install a heated 3 wire oxy sensor so it gets up to 500* or more. The old GM TBI computer is to slow to worry about the slight amount of time it takes the exhaust gas to get to the oxy sensor mounted out on the collector. I have a buddy with a one wire one that we put in the collector and I know it works in the summer but I do not know about the winter time, it runs OK in the winter so I have never hooked to it then. GM TBI is a pretty simple system but it would be nice to hook into it to see what the problem is. __________________ 89 YJ EFI AMC 360, T18a, D20, built D44, 14 bolt, 38" Creepy Crawlers.

04-17-2007, 10:38 PM	#2
94Dodge Truggy EX-Vice President Join Date: Jan 2007 Location: Fairfield, Ohio Posts: 3,048	Does it have an oxygen sensor and are all of the wires to it ok? I gave up on my wiring gremlin and had it professionaly rewired as simply and cleanly as possible by JN electric. I have yet to get it back and try her out though.

04-18-2007, 01:20 PM	#3
Hybrid Join Date: Mar 2007 Location: Fairfield, OH Posts: 134	The O2 sensor is brand new. I know the system runs in a closed loop until it gets warm, then it runs on an open loop. So I would think that since it runs pretty well until it warms up, that would suggest that something, maybe a sensor, is sending a bad message or maybe no message at all as soon as the loop opens. That is why I starting replacing sensors, but nothing has worked yet. Although when I replaced the knock sensor it run a whole lot better during that cold time.

04-18-2007, 10:06 PM	#5
Hybrid Join Date: Mar 2007 Location: Fairfield, OH Posts: 134	I will measure the distance of the O2 sensor from the manifold and let you guys know. What would be the correct distance for a 350 with headers?