Hey if you'd answer my questions in the increaed duration cams thread, maybe I could help you out...



hmmm....I feel like such a moron, I mean, this is my trade, I've worked on, fixed, tweaked and rebuilt pumps for more trucks than I can count. But this one has been giving me fits that just won't end. I suspected everything from injectors to motor mounts. QM, how about making a trip up here to the deep north so we can put our heads together on this *(&^#$.


Maybe this will help, I took a vid clip of the truck idling...

http://www.geocities.com/pro_gramma/MVI_0665.avi

To me, it sounds like the ECM is fighting something to get idle speed smoothed out and is either losing the battle or not functioning properly.... I wanna hear what you guys think.<!-- / message --><!-- sig -->

I looked through, and I don't see any questions that looked like they were intended for me to field, but I'd be happy to pitch in ;)

I think he meant in the Hydraulic Lifters thread. He asked you about the optic bump, then does it do it at various times.

My error, replace lifters thread

Anyhow, you d****d, with (adjusted) the optic sensor on this one right?

Did you change tstats (higher temp) when you went north?

Sorry for the edit John trying to keep it PG (Tim)

I've had the pump across the test stand and reset to spec several times, tried different H&Rs/optic sensors/housing/Transferpump/Cam rings/advance pistons/stepper motors etc... Some changes do affect performance, but I feel confident that I can completely eliminate the pump itself as being the problem.

TDG's rough idle can be heard here (http://www.canadianrigger.com/chevy/chevy.htm).

Mine sounds just like it on a cold fire for a few seconds. Sounds alot like and 671 at idle, i'll give my 2 cents here and say it sounds alot like timing to me?

I considered the same possibility, but from listening and watching the scanner, you can tell the PCM is cutting the fuel back to 0, then as high as 10mm(3) and back.

Find someone with a PCM and swap it out for a test or pic one up at the junkers. I'd loan ya mine from the 95 but you aint my next door neighbor!

I'm looking for a guy who works the GM parts counter who knows something about these PROMs. I think the best way to go is with a HD '95, take the vin to a dealer and get the updated PROM.

I think it might have something to do with the EGR system being non functional too, but I don't have my old LD manifold handy to try that either.

Sounds like the wrong pump is on your truck. Heard that before. Did you put the new timing chain set in?

New chain set just a few months ago and I've tried both pumps (5068/5521).

Did it do this before the timing chain change out?

yes, I was hoping that it would cure it. Interestingly though, it did change it some, it was a higher frequency afterwards than it was before. Just as severe, but the bounces were quicker.

I'd try another set of injectors just for grins.

2 sets of 6.5s and even tried a set of 6.2s!

Anything you can name from the heads, harmonic balancer, fuel system, even alternator, batteries and grounds, I've tried.

Bad lifter, rocker or pushrod? Seen a bent pushrod on a gasser do that same thing. Too many revs.

(you know how deep i had to dig in my head for that one...damn i was 16 when that happened to me)

Try a infra red temp gun on the exhaust manifold and see if you can find a weak cylinder.

hmmm...the readings will be a little tricky on the pass side, with all the exhaust from the drivers side passing the 2 back cylinders....makes it hard to compare to the other side.

Could be a nylon keeper(s) has dis-integrated, allowing a rocker arm(s) to skew, with resulting miss(es).

A compresssion check could tell - remove all glow plugs to unload the starter, disconnect ECM-B fuse so fuel won't dump into cylinders, crank away, 6-10 rotations per gaged event.

Do you have a plug wire crossed?

Could be a nylon keeper(s) has dis-integrated, allowing a rocker arm(s) to skew, with resulting miss(es).
Pulled the valve covers and replaced all 16 keepers, noted very little wear on the rocker arms/pushrods as well.

Have you done the compression check?

A flat cam lobe(s) will cause the "lope" - rotate engine by hand, check lift at the rocker arms.

Also, two injector pipes crossed will allow the cylinders to fire, weakly, off the mis-timed injection pulses, which would appear more as a "lope" than a "miss".........

I can assure, I dont have a line crossed.

The flatted cam lobe is what I'm afraid of, I won a camshaft on ebay for 10 bucks, and I'm bidding on a set of lifters for 20.

So what circumstances surrounded the change? I am assuming it just happened one day?

How is the crank position sensor? No chance it was bubblegummed together?

Is idle like this at operating temp only, or does it do it cold too?

Have you verified idle fuel rate with tech 2, and what is it?

I seriously doubt that it is mechanical failure. Sounds like the optic is fudged too far

Replaced the crank sensor too. Does it more so once the engine is warm when the PCM drops idle speed down to 560, which I think is too slow anyway.

When I bought the vehicle, it needed serious work, the harmonic balancer was broken, heads were cracked, and it needed a windshield. It sounded terrible at idle with the balancer bouncing around, and I never drove it far because it got hot fast, I literally bought it, drove it to the shop and started taking it apart. Rebuild the pump, put new injectors in, replaced the heads with rebuilt ones and new gaskets. Started her up and as soon as I got back it started doing this....that was 2 years ago! So I pulled the pump off a couple times, even tried a different one (this was before I ever attempted the 'bump') and tried to just drive it for a while and see if it would cure itself. I thought I cured it like a dozen times, after oil changes, or trying different TDC offsets it sometimes wouldn't do it but it always came right back.

As I said, I've tried several different IP configs and settings. At the stock setup it shows ~9mm(3). NO CONFIGURATION fixes the problem.

Its hard for me to say its a mechanical failure too, I've tried just about every thing, going for the motor mounts or the camshaft/lifters next.

Just for grins, if not aleready tossed, scrap the optic filter harness.

I'd suggest trying to locate a loaner PCM and Eprom just for grins.

I'll assume you've disabled the EGR and blocked it securely?

I might also try and make the EGR system work again, since its only a problem at idle, which is the only time the EGR should be working, maybe the PCM is expecting the engine's idle characteristics to be different with exhaust gases in the intake?

Scrapped the filter from the get go, and tried it and even several others, no change. (I've got a chain of them thats long enough to use for a jump rope :)

I seriously doubt EGR to be culprit, unless it's gassing past the lower to upper intake donut gasket, when mine was bad it did not do what you are describing, but did cause problems on hard acceleration.

its a HD manifold, doesnt even have ports for the EGR so leakage is a non issue.

jd

Why don't you recommend a compression check?

Wish I'd'a thought of that, Bill.;)

And, as a side note here, just for the record - EGR does NOT, that's en oh tee, not, work 'at idle'.

EGR fuctions at heavy deceleration, as in coming off a freeway onto low speed service road, and at heavy power-demand, where combustion temperature is ecxeeding high, to control Diesel emission.
Depending on rate and period of deceleration, PCM will call for exhaust gas recirculation down to just above idle rpm.

A leaking or open EGR valve at idle would cause heavy 'loping', and\or shut-down.

Just for the record..........:cool:

Yes, I'd like to read what compression you're making.

I guess compression test it is....I guess I havent' done it because i'm afraid of what I'll find.:eek: I kinda hope I find something wrong to explain the problem, but I'm not ready to buy a short block just yet.

I've seen several trucks that only run on 7cyls that don't do this though.

Install the the new free flowing muffler i just posted.... maybe that'll help..

That 560RPM idle command sounds out of spec or like an old calibration.

It just sounds like the fueling is too aggressive at idle.

Does it smooth out in gear with a load on it?

The 0-9-0-9 thing would tend to indicate that, also, but the compression check would say why - or why not............

Yeah, but if the compression were wacky, it would start hard, and should have a distintive miss. This situation would seem to present itself as more of a random miss much like a soft touch rev control.

As we approcah the point of too aggressive on the encoder bump, we see it touch on 0 occasionally. It will be worse when fully warm and no load. Now if one goes way too far, it may well act as described. I wouldn't know as I never pushed one that far.

FYI, my Dmax LLY acted the same way on a program that was fueled too hard down low the same way...

I might also try and make the EGR system work again, since its only a problem at idle, which is the only time the EGR should be working, maybe the PCM is expecting the engine's idle characteristics to be different with exhaust gases in the intake?

Scrapped the filter from the get go, and tried it and even several others, no change. (I've got a chain of them thats long enough to use for a jump rope :)
You may want to reread the way the EGR works, it should not be doing anything at an idle. Least that has always been my finding. Only time I see vac at the egr valve at idle is when the solenoid is leaking vac thru it.

That 560RPM idle command sounds out of spec or like an old calibration.

It just sounds like the fueling is too aggressive at idle.

Does it smooth out in gear with a load on it?
Thats exactly what I have been thinking, too slow, and fuel curve too aggressive to maintain that speed. PROM upgrade, probably to HD model with higher L.I. and no more EGR control.

Smooths out with just 1% APP, and the engine doesn't even speed up, it stays at 560 and smooths out like normal. Same if you drop into gear or hit the A/C button, any load or change will clear it up.

Talked to a Stanadyne trainer and he said your RPM's are to low and a computer reflash at the dealer would probably cure the problem. He also said dealers are unwilling in most cases to do it. The reason being if the computer craps out on the reflash they may be held accountable. He said dealers want you to buy a new computer before they reflash it. So shop around I guess.

Aha! Definite confirmation that it is a programming problem ;) Thanks DP!

Thats kind of the vibe I got, I had to call 3 dealerships before I could find someone who spoke 6.5 and ECM PROMs ;) And he still wasn't much help. I'll order one soon as I get a chance.

Might try your local salvage yards and pick up a good used one. I heard there are some models that are more desirable than others. New computers come from the dealer blank and require reflash in the vehicle.

You can't reflash a '94 model.

Back to my earlier thread, the idle sounds too low, try a loaner eprom and/or ECM...



Talked to a Stanadyne trainer and he said your RPM's are to low and a computer reflash at the dealer would probably cure the problem. He also said dealers are unwilling in most cases to do it. The reason being if the computer craps out on the reflash they may be held accountable. He said dealers want you to buy a new computer before they reflash it. So shop around I guess.

Thats exactly what I have been thinking, too slow, and fuel curve too aggressive to maintain that speed. PROM upgrade, probably to HD model with higher L.I. and no more EGR control.

Smooths out with just 1% APP, and the engine doesn't even speed up, it stays at 560 and smooths out like normal. Same if you drop into gear or hit the A/C button, any load or change will clear it up.
Well then just bend the pedal some, so the TPS doesn't come all the way back to 0%
there problem fixed
:)

Well then just bend the pedal some, so the TPS doesn't come all the way back to 0%
there problem fixed
:)

I don't think so Tim...:badidea:

just put in a '95 HD prom.

That HD program will at least get rid of that pesky EGR stuff.

I agree with you both, '95 HD, more power, No EGR, no Idle problems. But I think I'll splurge on a NEW one from the dealer, just so I know it has all the latest and greatest updates.

Here's my question. I obviously can't tell the dealer that I want to buy a '95 HD PROM for my '94 LD truck, one they'll try to tell me it won't work, then they'll tell me they don't know how to look it up. So I have to tell them its for a '95 HD truck. My question, is what truck do I need to pull the VIN off to make this work? Does it need to be a 4wd (like mine) or will a 2wd work? I assume it needs to be an automatic, so manual tranny's are out? QM I know you swapped yours out to run that 5288 pump, and I know you did discuss it on the forum some time ago. Do you think that I can just order the same PN # you got and it will work? I just want to get it right since I have to pre-pay for it and there's no garauntee on electronics.

Tex, I can get the prom ID from the '95 ECM I bought and GM can reference that.

ECM

serv. no. 16212488
code BPAA

Prom ID

BPAA
1621
6871

I suspect you would want a K to K prom so it would recognize your 4x4 stuf, I went S to F 98 to 99 PCM with no problem.

My truck's are all K3500.

I wonder what the difference, if any, there is in the PROMs for 1500-2500-3500 as far as advance, fuel tables, shift points etc? Might there be an advantage going from my LD 1500 to a HD 3500?

You mean other than the PCM not looking for the EGR/baro signal for boost demand.
I saw 65mm3 peak and 63mm3 steady on an unbumped '95 HD. Next time I have time I'd like to see what my "bumped" fuel delivery is.

In my 98 S vs 99 F PCM there was a difference in peak fuel request don't know if same applies to OBDI chips 63 mm was max I ever saw in S PCM, 70mm is what I recall seeing in stock F PCM, also boost vs fuel curve was different, fuel/boost stayed in longer on F PCM. I don't have a stock F PCM to check anymore.

Before Heath reflash & now JKs reflash only "performance" offering was a Z industry carried by many vendors, difference between a F stock PCM & Z reflash was negligible IMO, S PCM vs Z Ind was a big difference, but almost got same gain by just going to a F stock PCM, which was only $125 at junkyard, I have also found PCMs for cores as low as $75.

$600 plus core was going rate for Z reflashes. So I ran for a long time with a F PCM sent the Z back to vendor. I would suspect same would apply with a chip, if you have a T2 or MT2500 access you could know for sure, or call either Bill or John they could probably fill you in just as easily.

Next time I have time I'd like to see what my "bumped" fuel delivery is.
Changing optic sensor will not change the max fuel demanded by the computer. Its not calculating how much fuel is delivered, but simply showing how much the computer expects that the pump is putting out.

I got fed up with the engine surge, and managed to wrangle the truck away from the wife so I could hook it up to the scanner and see why my SES light was on. I got Cyl #4 contribution fault (cured in another thread) and a couple EGR codes...so I watched the EGR duty cycle while the engine was idling. EGR duty was pulsing wildly from 80 to 30, and BARO pressure was doing the same. So, I took a bottle of WD-40, and squirted it into the hose to the baro sensor. Did just what I hoped it would, the Freed up the EGR control solenoids and the readings normalized. Cleared the codes, and this weekend fixed the GPs and injectors, idles smooth as a mink's behind!

TDG you need the EGR for any reason; it can be bypassed & unbypassed very quickly without setting codes, a shim blank off plate plate under it, all controls function & gasses don't flow; PCM is happy and none the wiser EGR isn't flowing & diluting your mix

TD, see sig, (HD intake) no EGR ports

Now I'm real confused with your surging fixed with WD-40 in EGR sol, must have been pulling vac from WG also as they are on common manifold, If you are going to run that way with the HD manifold I'd find me a F PCM about $75 and only bother with plumbing to the WG, you could then cap off the lines to the other stuff, PCM would not monitor it not working, & it would be there for a visual inspection but the solenoids sticking would not have any effect on your WG's working. In F PCM baro comes from boost sensor at start up so a problem in the firewall one goes also, you could also gut honeycomb or bypass your MAF and get a little more flow. At lest that is what works on OBD II might have to experiment some to make the changes for OBDI I've never toyed with one of those.

'95 K L65 PROM is my next upgrade for sure, no EGR, faster idle, more power ;) I don't have a MAF sensor, only '98-up LDs

It wasn't just the WD, putting the GP back in the hole was the bulk of the problem.

You might benefit from a stock L65 prom, I ran that way myself l65 PCM almost 2 years until a viable reflash came out, would enable you to bypass all that parasitic EGR stuff still in the loop you ain't using like EGR vent and supply sols.

I'm confused, didn't I just say that?

94 and 95 F engines still get the BARO signal from the BARO sensor on the firewall. 96 & up F engines get it from the MAP.

Right, So I'll just keep the BARO sensor where it is and lose the EGR solenoids/hoses.

RJ it's really OBDI and OBDII and OBDII had test models out in '95, just ask TD.

MY bad I was thinking early S was like later S all solenoids are on common vaccum system with WG sol at end of the line, a problem in one causes problems in the whole gang, what had me wrapped round the axle was you saying your EGR ports are capped by F lower intake, but you still have EGR solenoids, and spraying WD-40 in EGR solenoids fixed your funky idle.

In later S engines after firewall sensor gives baro signal at start up, it gives feedback of EGR vent, so just unplugging EGR sols and straight plumbing WG sol only sets a code as PCM looks for EGR inputs, which is why I had to go to a F PCM so I could unplug my EGR sols, firewall baro/EGR FB, & MAF. Apparently OBDI & II differ in this regard.

'94-'95 "S" EGR engines get EGR sensor on firewall, tubed to the EGR solenoids.

2500 and 3500 with "F" also get a firewall-mounted sensor, but for BARO input.

Is the PCM in those years dumb to EGR position, sounds like from your description you have EGR command & EGR vent but PCM isn't monitoring how much venting is going on. For sake of enlightenment & education; do it, & if it do, how do it werk, in OBD I.

Turbo feedback is Boost pressure, proportional to duty cycle of applied vacuum to wastegate.

EGR feed back is direct duty-cycle controlled vacuum, measured thru EGR Sensor on firewall.

O2 sensor would do this function in gasser EFI.

Well (&$% back to the drawing board

Surge is most definitely not fixed, much better than it was, just a gentle bounce occassionally now. Looks like I better order that HD PROM...

You know, I think I'll get motor tranny mounts put in while I"m at it, if they're not causing it, no doubt they're battered pretty bad from the way this thing has been running. Same with the harmonic balancer, I tried 2 used ones that I knew were only marginal so I'd better break down and get a new one...hmm....bonuses coming up soon, I might just have to hold out a little longer...