Vince's TBI woes, progressive revelations, and tbi mods.

Ok, so most of you heathens know me, "hi my names vince" (waves)

Im not a total caveman when it comes to our trucks, and im namely the most familiar with the 87-91 tbi trucks.
My problem stated in the title isnt like "all of a sudden" , its gradually getting worse i feel.

I have some ideas as to whats going on, but im looking for suggestions to bounce off of.

List of work done so far to eliminate anything
Tbi overhaul
Motor is crate motor, with 30k miles, makez 330/385 at the crank.
New iac with relearned idle
I recently checked resistance at TPS, no issues.
New cts
New knock sensor (was causing issues)
Ignition module replace with another oem (old died)
New cap, rotor, plugs, wires, less than a year ago
(I dont drive alot, so no reason to suspect them as being excessively worn)
Exhaust redone, cat delete, straight 3" pipe into flowmaster 40.
Motor makes steady 22hg at idle. (Just checked)
New 700r4 built for 600hp


I just checked to make sure a plug wire didnt come loose (no misfires anyways)

1. What i suspect?
My EGR doesnt hold a vaccuum anymore (worn diaphragm) so as a result i get random egr codes at times, so its possbily causing issues When it attempts to pull a vaccuum at the egr module.
(Considering duct taping vacuum gauge to windshield and going on drive @ 55mph to see if i suddenly lose vaccuum)


2. Ignition module thats worn out (came from another tbi motor)

The power is every bit there on the low end.... i can flat leave about anything from a stop, but top end really sucks butt, if i downshift to 3rd or 2nd, and give it mid throttle, it climbs EASILY 20mph in seconds.

But anything at wot: its not exactly where it once was. Something has changed.


There is no engine codes atm.



Anyone with actual exp in tbi motors have a suggestion?


@1987 GMC Jimmy
(Sorry for pinging you buddy, but you're knowledgable on these as well)

 

This is an easy one. SHITCAN it !!! You know what to do.

 

Mf

 

How about fuel filter? I would definitely check fuel pressure while monitoring if possible.

 

Oops, i forgot to mention that part.
Fuel filter and pump are less than a year old.

Gas tank was cleaned as well from sitting for 7+ years

 

Just checked cylinder 1-4's spark plugs, all clean burns maybe a tad bit on the rich side, but i dont have appropriate gap for the compression ratio to effeciently make a combustion cycle.

I need .05-.06 for 10.5:1, i have .035 because im running stock igintion. (I have plans to upgrade that soon )

 

The EGR coming open can cause those issues. You might be generating enough backpressure in the exhaust at WOT to be pushing the EGR valve open. I've seen a test somewhere specifically for the TBI motors, you might try the allmighty google and see if you can find a procedure to check all the EGR functions on your motor.

 

Ah at last.
@Bextreme04
I know youll have good suggestions.

 

Im patiently waiting on a new PROM chip for my truck... will boost hp and tq 35 points min as well as delete the egr circuit, following that ill block it off with a plate i machine up.........

Im not giving it a whole lot if thought until the chip arrives.... but your thoughts are on track with mine there.

 

You might wanna just put the plate on it and see if it helps even without the PROM. I'm not super familiar with what your EGR setup looks like, but you should be able to block it off functionally while still leaving it connected enough to not throw a code(at least long enough to see if it fixes the issue you are seeing). EGR is the epitome of emissions nonsense and I refuse to have it on anything that I don't have to.

 

Amen to that shit!

Its a simple, yet dumb stamped steel body with a rubber diapraghm in it.

Theres a seperate module that pulls a vaccuum on it.

Blocking it off would be easy.

 

What about filter sock on the pickup and, is the gas cap venting?

 

Filter sock came with pump, should be ok id think


Not sure about gas cap

 

If there is a sucking sound when you remove the cap after a daily run . . .