Tbi 4.3 Troubles

Ever since I built my 4.3 it's been a pain to tune and has never been "right".
It is a 1985 block, heads, crank, rods, valves, rockers, pushrods.
It has higher compression light weight pistons, these are 350 pistons (the machine shop kept 2)
It has a decent cam that was purchased as a kit with lifters and timing set.
Everything is neutral balanced and I'm running a very heavy flywheel and the harmonic balancer and timing marks do not line up.

1008121846 by Joe with a jeep, on Flickr

1008121708a by Joe with a jeep, on Flickr

The carburetor set-up required a large cap hei which was commonly getting bumped into the firewall and i hated everything about carburetors. The tbi setup starts the first time every time but after driving 2 miles across town I stink, absolutely awful pre-ignition or something. The motor wants to Rev but gets choppy and backfires out the exhaust. I shift early and it will lug up a mountain but I still stink...
Help!!! Where should I start?

 

What injection system are you running? I had very similar symptoms on one that I tried. Changed it out and eliminated all issues.

 

OBD1 ?
Do you have a scan cable?
https://obd2allinone.com/products/aldlobd2u.asp

It sounds like your issue happens once the system goes into closed loop.

 

I put the 4.3L stock system on a 4.2L I6 AMC years ago. I also converted a GM 250 I6 distributer, installed that and made a few changes so the timing and fuel were controlled by the GM computer. I now have an Affordable Fuel injection system on my YJ 4.2L with a DUI HEI not controlling timing with the computer. Like stated above, I would check for a code on the ECU. If it's controlling everything you should get a clue.

 

@oldtime @Buildflycrash
Do you guys have anything else to add with the symptoms, this is same stuff I've been fighting when you rode.

Ahh yep skipped a paragraph. The current is a 90's gm based TBI system from Affordable fuel injection. One O2 sensor, water temp, map sensor and the tbi itself.

I don't have that one but I have this guy in the metric toolbox:

OBDMONSTER ELM327 FORScan OBD2 USB Adapter for Windows, ELMconfig Scanner with MS CAN/HS CAN Switch for F150 F250 Car and Light Truck, Diagnosis on Windows with V1.5 PIC18F25K80 Chip https://a.co/d/38LeAaI

 

I don't think you can make that cable work with the earlier GM system.
There are a 2 different styles on OBD1 cable connections, 12 pin and 16 pin.
Is your check engine light operational?

 

You should be able to retrieve the codes set by the check engine light. I have not done it in a while but it's something like turning the key off and on a few times in a row. Then leave it on and it will start showing you the codes by flashing the light and you counting. Should be able to find it on the innerweb. Affordable can help you too.

 

You can flash code it by jumping pins A&B at the data link connector. It will flash 12 first, repeated 3 times, then codes. Also check hose to the MAP sensor and the ECT connector. How big of a cam did you install?

 

What exactly does that mean? What is the Affordable model or kit number? Did they provide any installation data, setup instructions, troubleshoot information, etc.? I agree with Kyle in as much as it sounds like it is going rich when closed loop takes over. Either the system isn't self-tuning or has never been properly tuned.

 

Ahhh it's got a 33 code. I bet the map hose is cracked or a wire is snagged.
I'll check it out tomorrow, it's cold in the work parking lot without a top or heaters.

 

This is just the "legacy TBI" kit very similar to what Howell provides. Just a bare bones system that adjusts to the o2 a little on the fly but there is no self tuning. It uses a refurbished 90's pcm and Throttle body with a new harness and sensors. The fella that did the tune was the seasoned pro so I'm confident it is something simple that is on me to fix I'm just not too keen on what the smells and tastes indicate.

 

I would put a dial indicator on piston number one. Remark the balancer for TDC. Adjust to 12-18 degrees BTDC.
Symptoms sound like it is firing late. Unburned fuel blowing out the pipes.

 

That is a concern I've had. I'm running a short water pump which is inline with the timing marks. Adjusting the distributor is another "process" where I have to disconnect a plug and set timing to 4deg (verify) at such and such rpm then the pcm adjusts it from there.

 

Pulling the code earlier.

 

Guessing 33...map sensor {low vacuum} but is that because it is not running or an indication of something else?
I still say timing retarded which would give low vacuum.

 

You could do as UT says and just give a nudge of advance. Can't hurt.