95 K3500 (454) tuning issues

[454/4X4]

I bought this truck used with a blown 4L80E....I couldnt drive it, so I put alot of $$ into a rebuilt trans, and when I finally got to run it...I found it idled at like 1200 rpms. I found no air leaks anywhere, after much diagnostic work I decided my problem was in the PCM or PROM. I bought an identical 16197427 computer, with a 350 chip in it. It idled, but wouldnt even rev up in park hardly...obviously, underfueling.

So I put my old BMHM prom in the ECU, and it ran the exact same as it originally did...revved in park, but idled at 1200, or slightly lower.

So I contacted TBI chips...they said it probably wasnt the PROM and I did numerous tests, to rule out...again, air leaks. I found none.


So Brian burned me a BMHM chip, stock tune..nothing aftermarket or modified...STOCK. I plugged it in and Voila...Idles at 775-800, goes into gear so smooth.
I take it out to romp on it, and I doscover it has no guts beyond about 2000 rpms, and actually will go slightly beyond 2000, then go below 2000....its trying to rev, but cant.

Truck has no cat, so thats ruled out. New Fuel pump and filter.

So...TPS tests perfect, revs decent in park, has some stumbles off idle, its not smooth....but there is no "dead miss" feel. The plugs, wires, cap, and button are new. Timing is 4* BTDC with the brown wire unplugged.

I cant see a schrader valve to check fuel presure so I mguessing you have to T it in on this setup? Ive got a new FPR on hold at autozone, I figure its just good measure seeing as its probably the 20 year old original on it, and this one appears to be adjustable...or able to be made adjustable...

Any ideas...or did I get a bad chip?

[dave w]

Seems to me, you have covered the most common issues. I "T" the fuel pressure at the fuel filter. Maybe a data log will show something, not real sure. Things like injector pulse width, BLM, knock retard, spark advance, IAC steps, and INT can be very helpful. Monitors are another good tool within the data log.

dave w

[EagleMark]

I just can't figure that out? Sounds like your origanal Memcal had some errors set and was in Limp Home Mode? What was Check Engine light doing?

Replacing the PCM would have cleared codes but with wrong chip in Memcal could have easily set enough codes to go LHM again?

Now you bought the same thing you had and it's running without codes set and no LHM. Problem now seems like not enough fuel. Just because you put a new pump in does not meen it's a good pump. Actually most cheap pumps from parts stores are failing rapidly lately, there's also a possibility of old fuel and the fuel filter is going to be clogged or half full of water from the E fuel out now a days. How old is fuel? How long did truck sit?

As Dave said fuel pressure gauge for these get's hooked at fuel filter, check pressure.

Without a data log there's not much we can see? Do you have a scanner to check codes and data?

On to the next problem... why TBIChips would sell you a chip that was Superseded twice I have no idea? But then again there's loads of his problems all over this site and other sites!

BMHM Supercede

57-65-09 DTC 32 under load = Replace EPROM to BPRK

67-71-53a No upshift 2nd gear after cold start DTC 87 high ratio Error = Replace EPROM to CAJR

[454/4X4]

The PROM he sold me is a CAJR, he said that BMHM was an old old BIN file...and that he had the most recent one.

I get no SES light, but it is working as it comes on, on startup. Thats the oddest thing...it never sets a code unless i manually unplug something.

The FP was put in a few months ago, previous owner daily drove it, then got it stuck in a field hooked to about 10,000lbs of trailer in 4LO, and puked the trans. It sat a month or so, I put 15 gallons of fresh 93 Ethanol free in it when I got it back from the trans shop.

Im going to put the old BMHM back in, and test drive it, and see if if actually does run better with the only change being the PROM.

But it seems like, I dunno...when I look at the spray pattern at idle, its like I can see it pulsing...could be the lower idle, vs previously. Its 300rpms lower than it was prior. It doesnt look like its fueling like my TBI 5.7 does on my 94 Z71...If I take the 350 and manually rev it, the spray patter is aggressive and actually will spit some vapor back as it reverbs off the blades. On this...it doesnt get that aggressive, it just seems like a couple cones of fuel until I got like..way deep into the throttle, it comes alive then. But, like I said..I took the TPS and put it on a meter...red lead to blue wire, black lead to ground...and slowly moved it from idle to WOT and it was smooth as silk on transition...56v at idle, 4.45 at WOT.

[EagleMark]

Well that's good you got the right one.

Can't say I've ever seen or heard of a prom going bad? Well unless it had help from a human... still pretty hard to do. The problem you are left with still points to a fuel issue. If your going to own one of these you should really own a cable to datalog and diagnose stuff! Best tool you'll ever own for that truck! Can be used on all OBDI vehicles too.

[454/4X4]

Thats one of the problems Ive had, finding someone to sell me a PROM, because as Ive been told by dozens of people, unless you go in and screw it up, they just dont go bad like that.

I really should invest in some scanners or whatever...Ive got a few trucks, thus far this is the only one Ive had a "tune" problem with, and Ironically, its the most stock one of them all.

Ive got a
97 C3500 GMC Dually, with the vortec 454
95 K3500 Chevy, TBI 454
94 GMC Z71, Reg cab, stepside
95 F150 5.0 EFI 2wd

[454/4X4]

okay, new FPR and filter installed, made no change at all. I put the BMHM chip back in, and voila...runs great, but idles too high like before.

So..this new PROM is either underfueling or pulling too much time out of it...

[EagleMark]

You may be the first verified case of a chip or memcal gone bad?

Or the new Memcal you got has correct chip burned but on a V6 memcal netres?

Now if you bought a cable that would work on three of the four vehicles in your signature? We could get some data and at least have a clue why?

http://www.gearhead-efi.com/Fuel-Inj...uy-ALDL-Cables!

[454/4X4]

Is there any way to physically ID if its a V6 or V8..like...numbers or serial or something? Something I did notice, when running the new PROM...the injectors seemed to "pulse"...vs being a smooth constant stream of fuel...I attributed it to idling slower..and being noticeable?

If I get those cables...what do I do with them...I dont have a laptop to plug them into, just a desktop.

[dave w]

Is there any way to physically ID if its a V6 or V8..like...numbers or serial or something? Something I did notice, when running the new PROM...the injectors seemed to "pulse"...vs being a smooth constant stream of fuel...I attributed it to idling slower..and being noticeable?

If I get those cables...what do I do with them...I dont have a laptop to plug them into, just a desktop.

If you get a slightly modifed stock chip, that includes removing the ESC, the V6 memcal / resnet issue is removed as a possible cause.

Send me a PM if your interested in buying a laptop computer / ALDL cable that's plug and play ready to data log with TunerPro RT.

dave w

[454/4X4]

Well, I asked him for a bone stock tune...as it was 100 dollars ,vs 170 for a modified tune. So, everything should be as GM intended, id hope...I often hope incorrectly though.

If you get a slightly modifed stock chip, that includes removing the ESC, the V6 memcal / resnet issue is removed as a possible cause.

Send me a PM if your interested in buying a laptop computer / ALDL cable that's plug and play ready to data log with TunerPro RT.

dave w

[EagleMark]

The issue that has always come up with tunes from him are they come on a memcal. Right? You got the entire memcal with blue cover? Not a chip with an adapter that plugs into your memcal?

In the memcal is a Netres chip and a knock filter as well as the chip. He erases the chip and reprograms it. Now is the netres and knock filter correct for your truck? There are many differant combinations! We have found a few with wrong netres and many with who knows what knock filter because we have never figured out entirly GM strategy for numbers on knock filters. They must match knock sensor to be accurate.

I just don't take chance into tuning. This is why I use a new chip and a Moates adapter along with a new chip so there's no questions on what I changed, it's just the tune on the chip. Simple and accurate.

There's always a chance of a bad burn but it will come up in Check Engine Light normally. At key on, no start, does your CEL come on, blink and stay on until engine is started then go off?

[454/4X4]

Yeah, I got the complete unit, blue cover, etc...

If I could just go into the original chip. and program it to idle at the right speed, id be set...thats what my original problem has been all along...starts right up, idles at about 1100....after a minute the vacuum pull off releases and it idles down ot about 1000...and holds there.

With the new chip, it cranks right up, and idles much much lower...just, not smooth at any point in time at all. And wont rev up.

[EagleMark]

My guess from what you have told us and no data...

Your stock memcal/chip is fine and you have a mechanical issue like a vacuum leak. Chips don't go bad and even with human intervention it's hard but they don't change, they fail.

Your memcal you got from TBIChips.com is in a V6 memcal? Or wrong?

[454/4X4]

My guess from what you have told us and no data...

Your stock memcal/chip is fine and you have a mechanical issue like a vacuum leak. Chips don't go bad and even with human intervention it's hard but they don't change, they fail.

Your memcal you got from TBIChips.com is in a V6 memcal? Or wrong?

The thing is, with the other 2 memcals Ive put in it, it idles right down to the proper speed.

If I put in the original chip, turn the key on, count to 10..and unplug the IAc...it will crank up and run, but idles extremely low, indicating there are no vac leaks, beyond the air allowed past the butterflies for base idle. As soon as I plug the IAC in..it idles up.