New & in need of advice

[Jeepndan]

Hello everyone great form you have here, from what Ive seen and read so far everyone seem up front, honest and helpful.
I have a bit of puzzle on my hands, any and all input would be greatly appreciated. I have a TBI 350 w/ 700r4 in my 1985 Jeep cj-7. I realize it doesn’t fit this form exactly with it being a Jeep but the drivetrain, engine and transmission are out of a donor 1989 k5 blazer. I did this conversion myself over 20 years ago and it has run flawlessly up until 6 months ago. I purchased a GM Performance TBI 350 all stock (love the reliability) and had my 700r4 rebuilt. After Installing it, it ran beautiful but not being able to leave well enough alone, I decided to install a set of ceramic coated JBA smog legal headers. (I live in California)

The puzzle i’ve been chasing after the install of the headers is, it starts fine, idols beautifully but I am unable to accelerate without stuttering and backfiring violently 0-15mph is the extent of speed I’m able to reach anything above that causes a violent loud backfire. I’ve changed spark plug wires, spark plugs, brand new distributor, and O2 sensor single wire. Currently in the process of installing a three wire heated O2 sensor, I had a completely new exhaust system installed (original design smog legal system) from the headers to the tail pipe. Could improper back pressure in the exhaust system be a cause of this issue? I’m running out of parts to replace and ideas. Does anyone know if installing headers on a TBI motor simply doesn’t work. I’am completely puzzled as to what might be wrong any help would be greatly appreciated.

Thanks in advance for any and all input.

 

[75gmck25]

Headers will improve flow and will usually lean out the mixture, but the TBI computer should be able to compensate if the O2 sensor is working properly. Does the TBI computer have an OBD interface plug where you can get a reading? I've only worked with carbureted squarebodies.

Bruce

 

[Arkansas_V8]

Headers are fine on a TBI. I run hedman longtubes, with only 4 feet of 2.5" straight pipe, and with no 02. On cold days I have to let it warm up, other than that it's all good. I did have a similar situation but it was my tps, or IAC, hell maybe my CTS. One of those darn sensors.

 

[Charlie]

 

[78C10BigTen]

Not to insult but id start simple and make sure all the plug wires are correct and tight

 

[Jeepndan]

To 75GMCK25, I do have an OBD interface I will give that a try, the trouble light has never come on but it may have a stored code I might have missed. Thank you Arkansas_V8 I will checking all sensors this morning, I believe there are only a small hand full of them. TPS, IAC are the two major players, If all else fail I’ll just replace them all, hate to spend money replacing a good sensor but at this point peace of mind & a running Jeep will go a long way. I wish I could run No O2 sensors and straight pipe but California is way to uptight for that mind set. lol
Thank you Charlie for the Welcome, much appreciated.
78C10BigTen, No insult taken..that was one of my first thought, that I had crossed a plug wire but all plugs are gaped correct, boots are snapped on and in correct firing order. (I even switch over to a Accel shorty header plug for more clearance)
I’m about start my new round of trouble shooting, I’ll be sure post any new findings or fingers crossed a solution to this problem.
Thank you everyone for your suggestions.

 

[dvdswan]

Welcome to the site. Timing or vacuum leak?

 

[CorvairGeek]

"I purchased a GM Performance TBI 350 all stock"

Are these roller or flat tappet?
I hate to say it, but it almost sounds like a cam going flat.

 

[Jeepndan]

Thought I would pop back on for a fast update, Timing is dead on, idols perfect! About to check for vacuum leaks and bad sensors.
The funny thing is it ran perfect not a hiccup or backfire until I installed the headers and had new exhaust system built. I don’t think it’s a flat cam, unless it picked the same moment to act up as when the headers were installed, but thank you just the same..that never crossed my mind. Seem to run sporadically better after letting it warm up for 15 or more minutes (Thank you Arkansas_V8 for your input on that idea) tried that out this morning, just kept a medium to high idle going, seems to take off better but backfire and stutter now at 30-40mph. I was told the 3 wire O2 sensor would fix that issue.
Has anyone had better results with a 3 wire setup over the single wire style? For keeping the O2 sensor in a closed loop.?

My breaks over, back to figuring out the sensors now.

Again, Thank you everyone for your input, Much appreciated. I’ll update this once I rule out all my sensors for being the issue.

 

[Preston]

Welcome to GMSB from Virginia

 

[1973c10]

 

[bucket]

"I purchased a GM Performance TBI 350 all stock"

Are these roller or flat tappet?
I hate to say it, but it almost sounds like a cam going flat.

It does sound like a flat cam, but from what I've experienced, a flat cam will always have a dead miss at idle, in addition to the popping and whatnot on acceleration.

Did the O2 sensor wire perhaps get burnt?

 

[C10MixMaster]

flat cam didnt happen with the install of the headers. has to be headers/exhaust/ or something with the install.

a couple things to check if dealing with a smog pump is it plumbed rite if originally plumbed behind the o2 sensor and now infront? could do wierd stuff. is there something in the exhaust restricting it a rag fell in it during the install? check for damaged or pinched wires vacuum hoses crushed fuel line . open the hood, step back , walk through all the steps in your head and double check what you did. it did run before and the parts you added will not keep it from running.

 

[climb-101]

i would check for for dirty or cracked plugs. i have seen the porcelain part get dirty from people hands when they install and then the spark goes down the outside of he plug vs the inside. it’s easy to spot at night. best way i have found is have someone start it and hold the break while raving it up a little while its in gear to put a load on it. look at the head where the plugs are and see if you see a spark or a flash.

 

[K201979]

Welcome. I know nothing about tbi but it sounds like your heading in the right direction and i hear alot of good ideas flying.