It's a riddle

[Hybrid]

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]

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]

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]

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]

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]

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.

[Hybrid]

I have a dual exhaust with separat mufflers for both sides of the motor, 4 cylinders each. I put the O2 sensor (which is a single wire) on the passenger side exhaust, so it does not even see the other 4 cylinders. Would this be a problem? I also know that I didn't replace the IAC sensor, so i have no idea how old it is. I tried searching for codes the computer might be throwing by counting the engine light blinks but no codes came up, as far as i can tell anyway.

[Mike F]

Just one side of the motor is fine for the oxy sensor as long as it can see all 4 cylinders. A code 12 will come up when in the error code mode to tell you that you are in error code mode, the error codes will be between the code 12s.

A bad IAC will probably not set a code. The IAC may or may not be your problem. IAC stands for "idle air control" it is not a sensor but a little stepper motor controled by the ecm used to open and close a air hole that bypasses the throttle blades to control idle.

[jfiscus]

Yous hould be able to run w/o the IAC, if it runs well till it's warm then there is a sensor that kicks in when its warm, possibly a crank sensor? Also, are you buying name brand sensors or AutoZone/Advance sensors. Sometimes the sell you bad/wrong "new" sensors at these stores & you pull your hair out cause it's a new sensor & replace everything else when the new part itself was bad from the store.

(Had a couple buddys spend over a grand to finally diagnose their supposedly new/good sensors were bad.)

[Mike F]

NO the GM TBI setup uses the IAC to maintain idle at all temperatures and conditions along with a dozen other modes of control at other RPMs.

GM TBI does not use a crank sensor, the motor has a distributor along with a ignition module that sends a signal to the ecm that takes it and looks at the operating condition and decides how much spark advance is needed and sends a signal back to the ignition module to trigger the coil like any older electronic ignition.

GM TBI only has temperature, oxygen, knock, MAP, TPS, and speed sensors.

I can program older GM TBI systems and have set them up to run other brands of motors such as the AMC V8.

[sarge]

Jacob , you need to take the Chero to MikeF and let him get that thing running for you .

MikeF are you one of the MV4W's ? and did you wire Shawn B.'s YJ ?

Sarge

[Mike F]

Originally Posted by sarge

MikeF are you one of the MV4W's ? and did you wire Shawn B.'s YJ ?

Sarge

Yes and yes, I talked to you at the swap meet.

[sarge]

I thought so , Jacobs rig is my old one , it ran great with a quadrajunk on it so I know it's a FI problem. He sure could use some help on this one , and I really want to see the old girl on the trail. You rarely ever get to see your vehicle in action and not be behind the wheel.

[Hybrid]

Yes, I am out of ideas. i really want this thing running right! I have purchased all the sensors i replaced from NAPA. I have replased the ingnition coil in the distributor, the oxygen sensor (which now that I think about it, that one was from Autozone), and i replaced the knock sensor, which was from NAPA. Mike F. if you think you can fix it that would be great!! Send me your info and lets talk. Thanks so much for all the help so far!

Jacob

[Mike F]

What model ecm do you have? I just need the last 4 digits of the number. If they are 7747 I can program that one, if it is another number I may only be able to hook into it and see what is going on depending on year and model and what is left of the harness ;)

Ignition COIL in the distributor? If that is true it sounds like it is a car setup and a early one at that, what exactly do you have? We may have to go through it bit by bit to make sure it all matches somewhat.

[sarge]

Mike , I will start listing the parts that I sold him with the rig :

I got the intake and TBI off of a suburban with a 350 in it , it had a Holley TBI unit on it ( I guess Jacob found it was bad ) . I can't remember the year , but I would say it was early 90's .

Jacob ,
just to make sure , get the numbers off of the block , I never second guessed the guy I bought the K-5 off of as to it truely being a 350 , it may be a 305 and this would cause problems .......

[Mike F]

sarge, Did you pull the entire TBI system off the suburban?

I have the casting numbers for chevy V8s up to 86. At some point after that GM started to cast the displacement litre size (like 5.7) into the same spot as the casting numbers on the rear top of the block in front of the trans.

Hybrid, We also need to ID the replacement TBI you picked up to replace the bad holley TBI.

I can trace some of the numbers for some of the original GM parts. I can only read the info off the chip for the 7747 ecm to see what it is but it realy doesn't matter for that one because I can change it if need be.

[sarge]

the intake and TBI were already off the burb sitting inthe rear seat , I pulled the ECM out from under the dash and I can't remember is I found the dist. or not . The guy I got the K-5 from worked at GM and told me that he blew the 305 and put a crate 350 in it a few months before I got it . It looked like the standard Mexican 350 with the perimeter bolt valve covers that you can get for like $1400.00 .

The burb ( if I remember correctly ) was not the old square style ( 80's ) but more like a 90's . I have a 90 and it was still the square style so I don't know when they changed. I think the ecm is the 7747 , I think I checked when I was going to order a harness.

[Hybrid]

The number on the ECM is 1228747. Where on the block is the number for the motor? That motor might very well be a 305, b/c i bought a new 350 harmonic balancer for it and I can not get it to TDC for the life of me. The coil i replaced in the distributor was a little plastic thing with copper wire coiled around it. It sat underneath the rotor button and it was connected to the sensor in the distributor.

[Mike F]

I do not have any info on the 1228747 ecm but do for a 1228746, if it is a 8747 I can not hook into it and the only option would be to convert to a 7747 ecm if I was to mess with it.

The block numbers should be on the top rear edge of the motor.

That coil was probably the pickup and the sensor is the ignition module.

[sarge]

Jacob , don't freak if it is a 305 , I have all the 305 stuff off my Camaro.

[Hybrid]

The number on the block is 14010207

[Mike F]

Originally Posted by Hybrid

The number on the block is 14010207

That comes up as a 80-85 350 casting in the book I have. Looks like the guy may have not been to truthfull. Look at the top of the block (cylinder deck) right in front of the left head as you are looking at it, GM would stamp part of the vin code for the vehicle the motor was originaly installed in unless it was a crate motor, but I have the casting numbers for those up to 88.

I can run the casting numbers off the heads also. They are under the valve cover though on top of the head.

What wire harness do you have?

[Hybrid]

The place you are describing sounds like where I got the number for the block. The only other number I could find was on the intake manifold which is 14057055, i don't know if that helps or not.

I used a brand new wiring harness from a place called Affordable wiring, or somthing like that, it was awhile ago.

[Mike F]

The casting number was behind the right head and was in the mold when the block was cast. The other number in front of the left head is on the cylinder deck (ledge) right in front of the head and is a small number that was stamped on the block when the motor was put in the vehicle. It may or may not have one if they stoped doing it. It is where the saying "matching numbers" comes from with the old muscle cars and how you would know the motor was original to the car.