Weird 454 TBI problems.... as always

[munice]

Okay well my truck is being a PITA again.

Here's the deal, I've just got the SES light hooked up (swapped in 89 motor into an 87) but not the ALDL so i can't read the codes... These problems have been occuring since the middle of summer But i've been having some difficulties in hooking up the ALDL between the two harnesses.

**no solid codes apparent.. no SES light upon startup..

symptom #1: Driving either in town or on highway engine randomly looses power, (very off and on almost instant between weak and strong) chuggs if I try to accelerate, basically takes more pedal to maintain original speed, very annoying in town as the truck can almost stall if this symtom occurs when turning.. hard to describe, basically a very "pronounced" switch from a healthy big block feel to a "4 million mile small block" kind of feel...
*SES light does not come on.

symptom #2: Engine idles high (no not during starting... thats a noob question) .... actually the engine will idle around 1100 rpm at traffic lights and sometimes stays this way until the truck is shut off again. High idle happens on the highway aswell, I notice this when I'm trying to shift (I don't use the clutch much) The SES light does come on when ever the high idle symptom is apparent. I've noticed the SES light coming on and off on the highway before but didnt notice if it was idling high..

symptom #3: This is the rarest of one, occaisionally the engine will fluctuate rpms between 7-1000 at about the speed of " one mississippi, breath, two mississippi..." SES light does not come on.. does'nt seem to affect driving much if any, just sort of weird.

My theories include:

-TBI throttle body/manifold gasket (these seem to be a well known vaccuum problem child)

-maybe EGR? I've heard that they can cause problems noticeable in highway driving..?

-Bad TPS this im sure is an accomplice if not the sole problem... Just waiting to get a new one... right now ive got a TPS from presumably a 350/305 as it worked fine when i put it on but its visibly different than the original...

old symptom: originally me and my mechanic neighbour decided that my TPS was definitley toast as the truck would run fine until around 2100 rpm, then it would struggle... then above 2100 it would be fine again...

...so I swapped that TPS for one that a friend had he wasn't sure what it was from but it was GM and it fit... and for the initial test run it worked great! the truck ran amazing.. but then it started to have the aforementioned symptoms..


Sorry for the long rambling post but Its just such an annoying problem... It sure takes the cool factor out the big block swap

I might try the old TPS again, but If anyone has any ideas, or If any of you have had similar problems let me know. BTW i hope to swap the front or both of my new axles in this weekend, hope to get pics up!

cheers, Andrew

[rfmaster]

1) No SES on startup is bad thing. ECM pin A5 (brown/white wire) is connected to one pin of of the SES light, the other side of SES is connected to +12 IGN hot bus. You can read codes without a scanner provided that you have functioning SES light by shorting pins A&B of ALDL and observing SES light for DTC codes. Also, some ALDL interfaces have SES output (if wired) on Pin D - worth a check. Without SES further diagnosis is going to be tough. Normally SES should be solid on when ign is moved into in run position blink off turn solid again, before starting engine. Got to have this to have a fighting chance in narrowing it down.

2) Loss of power when running could be due many factors. Drop in fuel pressure, interment EST (timing control by ECM). Vacuum leak is unlikely.

3) High idle could be due to intermittent or sticky IAC. At highway speeds IAC is commanded to a wide open position. When decelerating and coming to a stop ECM will command to reduce the amount of by pass air by moving IAC to reduce amount of bypass air. If IAC is sticky or if there is carbon build up extra air will cause higher idle. Basic service should include removing IAC - cleaning IAC pentacle and TB idle bypass passages (if required). Since you do not have functional SES open or intermittent CTS may contribute to high idle. Got to have functioning SES!!!

//RF

[munice]

rfmaster,

might have misworded things... I do have the SES light when the key is turned to the run position just not while running (normal activity) What i was getting at was that i dont believe there to be any "hard codes" as in the SES light is not constantly on while running... so what ever is busted is just going in and out of the acceptable variable (still in the middle of reading your post....)

[rfmaster]

Originally Posted by munice

rfmaster,

might have misworded things... I do have the SES light when the key is turned to the run position just not while running (normal activity) What i was getting at was that i dont believe there to be any "hard codes" as in the SES light is not constantly on while running... so what ever is busted is just going in and out of the acceptable variable (still in the middle of reading your post....)

Some codes will be set and SES may not be lit! To pull codes use a simple paper clip jumper and short pins A&B on ALDL connector. Insert jumper between pins A & B, turn ignition to run, but do not start engine. If there are no pending codes in ECM memory you should see 12 12 12 - pause repeating again. If there are DTC codes pending the SES will flash 12 12 12 pause followed by code(s) repeated three times. For example, DTC 15 was set - CTS reads very cold temperature then you should see:

12 12 12 pause 15 15 15 pause 12 12 12 pause 15 15 15 and will keep on repeating.

Try this first - let see what is going on.

//RF

[yotehunter]

Hi guy's, I know this post is old and hopefully you will get this, I am having a similar problem. I have an 89 V3500 with 454tbi, when I am driving, if I try to accelerate after about 30 mph, it loses power. If I have speed up say approximately 30 mph and come upon an incline, the truck loses power and will not come out of it until I get down to a low sarting speed, approximately 10-15 mph. Even at this point it will not let me get into the throttle at all.

Now for the reapirs up to this point;
MAP sensor, Injectors, fuel pump, and numerous fuel filters.
When I replaced the fuel pump, I thought I had solved the problem. The truck ran great the day I changed it, then the next time I fired it up and drove it, it began acting up again. I cant drive it anywhere right now because when I get to an incline I lose power. I did notice the other day while trying to get to the landfill, that when I go down hill, as long as I do not apply gas pedal it goes fine but if I give it gas it tries to die out.

I am getting a little frustrated with this and it is getting close to firewood cutting season, I really need to get this truck going, I dont want to use my new pickup. Thanks for the help.

[rfmaster]

Originally Posted by yotehunter

Hi guy's, I know this post is old and hopefully you will get this, I am having a similar problem. I have an 89 V3500 with 454tbi, when I am driving, if I try to accelerate after about 30 mph, it loses power. If I have speed up say approximately 30 mph and come upon an incline, the truck loses power and will not come out of it until I get down to a low sarting speed, approximately 10-15 mph. Even at this point it will not let me get into the throttle at all.

Now for the reapirs up to this point;
MAP sensor, Injectors, fuel pump, and numerous fuel filters.
When I replaced the fuel pump, I thought I had solved the problem. The truck ran great the day I changed it, then the next time I fired it up and drove it, it began acting up again. I cant drive it anywhere right now because when I get to an incline I lose power. I did notice the other day while trying to get to the landfill, that when I go down hill, as long as I do not apply gas pedal it goes fine but if I give it gas it tries to die out.

I am getting a little frustrated with this and it is getting close to firewood cutting season, I really need to get this truck going, I dont want to use my new pickup. Thanks for the help.

yotehunter

Welcome to the board. It is better that your start a new thread. Just tittle it appropriate = " Strange 454 TBI problem " or similar.

//RF