98 K2500HD, 6.5L 4L80E 4wd, rough running, need to drive 200 miles, details inside.

[GM Guy]

Hello all,

We are trying to drag home the auction bargain 1998 Chevy K2500HD.

history: 2xx,xxx miles. 2nd engine at 25K or so, 3rd engine: less than 1K on the swap, 3rd engine was a 12x,xxx miled motor. no clue what year the swapped motor is, but if we werent informed of the swap, we couldnt spot it, looks just like a 98 motor. grounds have crimp connectors on, but all looked fresh and clean. seller stated it ran great for that 1K miles, then the guys (construction outfit) were in town, started running crappy, drove home and parked it.

When we got there:

At rest/stopped: it surges something terrible, tries pushing through the brakes, runs like shit in park, idles at 1100-1200 at all times. whenfist fired, it sounds really poppy, like the computer has killed a few holes. at that time it wouldnt even go to 2K RPM. also at the time, no SES light.
we tried reading codes, connect error. unhooked batteries, reconnect, got the SES light back, but after starting and stopping once, still no connection. so no codes.

lift pump pukes fuel out of the t-valve on prime.

on the road:
loves 1200 RPM, give it plenty of throttle, and it shoots through 1300-1650 RPM, settles in at 1800. early on, didnt find 2K, but 5-10 miles later, was able to gingerly find 2K. very erratic throttle. TCC seems to lock, 4L80E drives great, fluid slightly discolored.

parked for the night at a buddies place, but will return tomorrow to pick up. we are packing 2 PMDs (one w/cable and heatsink, one random one out of a project rig, both haven never been confirmed operational) a fuel filter, LP and o-rings. the LP pukes great, so wont do that, and fuel doesnt seem to be the issue. IS the PMD the cause, or is the IP going south?

any input appreciated, thanks!

PS, since the Code reader wouldnt recognize, I figured the diagnostic checklist wouldnt be as helpful, but if you want me to fill it out, I will.

 

[ak diesel driver]

pmds can cause that but I would be leaning toward a bad ground or connection or even a bad PCM

 

[GM Guy]

we might try grounds first, PMD second, and of course try and limp home and change the ECM last! I forgot what a pain 96+ accessory drive makes to get to the pmd plug, the 95 GMC stared at me plain as day all summer.

 

[WarWagon]

If the computer will not enter diagnostic mode it is defective or has bad voltage. Voltage aside of bad grounds can be bad from ignition switch, fuses corroded, battery cables, bad battery(s), shorted diode pumping AC out of an alternator, shorted sensor, positive connections corroded or loose...

OBDI for example: (Yes I know it is a II) has a specific voltage you should get at the paperclip terminals. You measure the voltage when the computer refuses to enter diagnostic mode with a scanner or paperclip. Low voltage and you start tracing wiring.

I would bring a spare computer, batteries, and alternator if you got em.

If it doesn't run right your backup plan should be to check Craigslist for people advertizing cheap towing. Cheaper to tow it when you plan it in advance.

I would re-do the computer ground because there are a number of ways to screw it up and look good. Then after checking voltages and connections noted above start unplugging sensors. Goal is to get diagnostic mode. Note: Have you used this scanner on a diesel 1998? Some scanners are simply FUBAR and will not read some vehicles like Snap-ON and 1995 GM diesels. Just saying.

 

[Turbine Doc]

Good recommendations above , plus a good lift at idle also does not preclude a bad one at load demand or plugged sock in tank, you need to do the lift pump test with gauge at power.

A partially clogged fuel filter will make it run like crap grab one of those, any comms code U100 on scanner?

My Burb when I 1st got it would not read, turned out bad ABS brain killed the comms I unplugged the ABS plugs from the ABS unit and cleared the comms issue.

PCM gnd is the one pass side rear intake/head stud, very important that one be clean & tight

MT2500 works on the OBD-IIs, the only one that is wonky is the TDCO value and I can help you with deciphering that once you get that far

 

[GM Guy]

everything to do with the batteries is clean and tight, so for now we might ignore that. the grounds all have crimp connectors, so crimping on the insulation is a possibility. code reader is a crappy little harbor freight unit. we have most definitely had it on a 98 C3500 ,but with a 350 vortec, and I am 90 percent sure we have had it hooked to the 99 chassis cab 6.5L, as well as the 96 C2500 6.5L.

I left my 6.5L toolkit in Idaho with the other rigs, so I didnt bring the guage for lift pump PSI.

No other parts brought than what is listed, and we are allready on the road (started at home in far west KS, picked up PU in south central Nebraska, brought it to a friends place in north central KS, went on to our destination in far east KS, will pick up combine headers and head back.

final note, does anyone else find it strange that we didnt have an SES light, then after unhooking the batteries we got a SES light?

 

[GM Guy]

everything to do with the batteries is clean and tight, so for now we might ignore that. the grounds all have crimp connectors, so crimping on the insulation is a possibility. code reader is a crappy little harbor freight unit. we have most definitely had it on a 98 C3500 ,but with a 350 vortec, and I am 90 percent sure we have had it hooked to the 99 chassis cab 6.5L, as well as the 96 C2500 6.5L.

I left my 6.5L toolkit in Idaho with the other rigs, so I didnt bring the guage for lift pump PSI.

No other parts brought than what is listed, and we are allready on the road (started at home in far west KS, picked up PU in south central Nebraska, brought it to a friends place in north central KS, went on to our destination in far east KS, will pick up combine headers and head back.

final note, does anyone else find it strange that we didnt have an SES light, then after unhooking the batteries we got a SES light?

 

[GM Guy]

ok, still un-defeated on being stranded in a 6.5L. ol bag made it home!!

runs decent under load, best at 50-55 mph and cruise set. if it lets off, it wil buck from 1200 to 2300, back and forth till you end the cycle by bumping it offf cruise or if you are on the foot feed, taking your foot off the pedal completely. btw, on the foot feed, if you ease out of the throttle, it will take off. take foot completely off, and it will return to 1100-1200.

TCC seemed to lock the whole time, but it was running rough enough it might have been playing with the TCC to dampen the vibes a bit.

tanked up, thre in 1/4 jug 2 cycle. put 150 miles on tank, never changed anything.

did try running at 60-70 for brief stints, but due to vibration, that was stopped.


OK, now that it is home, we will screw with the grounds first. the ECM ground is one of the ones on the rear of the motor correct? There was a few ECM fuses in the underhood electrical center that were clean and not blown. never studied the side of dash electrical center.

anything else to do to try and clean up the juice to the ECM to try and get a code reader to connect?

thanks for all the suggestions thus far, keep them coming!

 

[WarWagon]

The SES light on my 1995 is predictably weird. After you turn the key off the computer stays alive for say 30 seconds or so allowing me to read APP voltages etc. Turning the ignition back on during the readable time after key off results in unpredictable bulb check results. Specifically Service Throttle Soon and Service Engine Soon will be both off, one or the other on, or both on for the normal bulb check time.

Waiting till the computer quits sending data on the ALDL then turning the key on results is the proper bulb check sequence of both on then STS goes out.

 

[GM Guy]

ok, fiddled with it today. cleaned the grounds. during the motor swap, two of the three (possibly 4, since two were put together) grounds had been "re-done" with yellow butt connectors. they were cleanand crimped well, so I didnt pay them much attention.

the rearmost ground went like this: thread in stud, then chassis ground (the braided one) then a nut (looked new, hope it wasnt SAE on a metric stud. )then the two small wores in one yellow crimp connector, then the tranny dipstick holder, then a medium sized wire, then a nut.

the next stud forward had a lone big wire with the factory connector on it. I was able to get the medium wire unhooked, but couldnt get the tranny dipstick out (figured there was another bolt or nut, so I didnt try too hard for risk of screwing it up.) so I made a short jumper with an eye and a eye converted to a double prong, and I slid it iunder the trapped ground, and hooked it to the next stud forward.

after cleaning and reorginizing, the rear one goes: stud head, chassis ground (never actually un-did this, just sprayed wd40) shiny nut, jumper ground, two small wires in one yellow crimp eye, bracket, then nut. The next stud forward went: studhead, jumper ground, medium wire, big wire, nut.

cleaned up batter connections to be sure, all looked acceptable, but did a final cleaning and did the bolt mod on one ground, due to the poor condition of the OEM bolt. added a lock to the big main OEM bolt, as it was bottoming out in the batt before it was tight. WD 40 was used throughout, and old man showed up, so copper anti-seize wnet on lightly (we stuck two scredrivers hooked to a batt. charger in a can once, and used an tester, not one flicker of conductivity. IDK why he does it honestly) there was allready some grease on it. nice and clear, so I assume dielectric.

fired it back up, still hunts, surges, etc. less angrily now, more smooth, so the grounds did help (and getting the main stud tight helped the cranking)

I will check agin, but I DIDNT notice a service throttle soon light. the SES light came on, hooked reader up, no connection. it does get power, it lights up, and hunts through its operating system trying different OBDII formats, but then it gives up. same as always.

there is the noise filter to the Optical sensor, do I need to remove that? it looks fine though, but who knows. the PMD is quite the bitch to get to, so for the lazy man, should I try the throttle pedal? (I have a good one from a 95 and an iffy one from a 99, will the 95 work?)

final question, on the FFM, does the water drain rely on filter flow, or can the filter be clogged solid and still flow out the water drain? my old man says that we wouldnt get that kind of behavior from the truck if the filter is clogged, but the DS4 is allways full of surprises, so IDK. it is his truck, so he is being stingy on the filter changing.

 

[ak diesel driver]

I'm surprised a 98 has the noise filter, I'd heard they pretty much did away with them on the later obd2s. Most pitch it. the water drain is pre filter, best would be a pressure guage check before and after FFM and see how much drop there is across the filter.

 

[GM Guy]

well, this is its third motor (second off warranty) and he doesnt remember the year of the buddy's truck, the buddy did the swap also. so many unknowns. he was better than some swappers, at least it has the 96+ accessories!

if it is pre-filter, I think we will change the filter.

might as well pull the upper intake off and take out the noise filter and relocate the PMD and be done with it.

this will have to wait though, as I am off tomorrow in the 91 GMC back to idaho (Pray there is no salt on I70 yet. this truck has never seen salt in my possession, and likely its life). In Idaho I will be helping a buddy with corn harvest, perks include piloting the R70 Gleaner combine with the 779 cubic inch twin turbo charged, straight piped exhaust V-8 Deutz diesel. cranks out 270 HP all day long. (the twins and the straight pipes are factory issue Gleaner btw. Gleaner: the performance combine! first to the field with a turbodiesel, and with few exceptions, if it was turboed, it got a mandrel bent factory straight piped exhaust.)

 

[Paveltolz]

Is it still trying to push through the brakes and such? I'd rule out the fuel delivery first though, to include the tank sock. Pain I know but it is still a relatively inexpensive item to run down/rule out.
Not sure if another ECM is in your future or not but with it sounding as wonky as it does...long winter ahead and Craigs list / Ebay or http://www.car-part.com/ can be your friend. I picked up an ECM off Ebay for 635 (98 dually) a few weeks before he got on the road and it was fine

Safe journey out this way and if you're of a mind, you are welcome to spend a night here. No snow on the roads so far out this way, only a slight amount at the much higher elevations on the mountains. I'm a little south a ways from the I-70-25-80-84-15-84 route you'll probably roll, but if you choose to blow through Denver and ride I-70 to Green River (beautiful through the mountains there) and up US-6 to I-15 you'll run right by Orionthade and Jamin6.5 in Orem, and I'm just a few miles west of them.

 

[WarWagon]

The water drain is pre-filter. The filter doubles as the water separator so excess water falls off the filter and can be drained at the water drain. I am pretty sure you have everything but the "Oink!" out of that fuel filter... :hihi:

As far as the factory ground you can get off the stud - cut the wire. Then a new crimp connector can be put on and it grounded anywhere on the engine. Some like to solder the wire into the crimp as well. As long as it is a clean ground on the engine it will work.

If the computer is not entering diagnostic mode I would work on grounds and verify the computer voltage. Measure the cigarette lighter voltage to see if there is some positive side voltage issues and then you will have to measure the computer voltage. The APP isn't going to work right with bad voltage. The APP can short out so swapping it for testing can't hurt. IMO first I would cut the connectors off the grounds in the corner and redo them. Some trans dipsticks have a nut on the back of the trans bellhousing to engine stud.

You have to resist the temptation to swap parts before the electrical issue is solved. Rather than swap parts you disconnect things as a shorted sensor would be the only thing keeping the computer form going into diagnostic mode where it communicates with the scanner. Bad ALDL wires and connections are possible - but not before going through fuse connections, grounds and verifying voltages running.

To be clear a computer uses ones and zero's to work. A zero is off and 1 is on. There is a specific voltage that means 1 in a computer. If the ground is bad or the voltage is low the 1 output can be so low it is read as a 0, zero. This garbage out problem results in unintended results seen as poor engine operation. Analog conversions with bad voltage can trigger the STS light as voltages are out of range.

 

[GM Guy]

Paveltolz, thanks for the invite but I am taking the highway to save distance. I will be taking in the NPS store auction tomorrow, but then gotta jet up to idaho, the buddy didnt realize he needed me this soon, was shocked as heck the corn was dry enough when he tried it, so the heat is on, and he has farmers that hire him for custom work stopping by checking progress. maybe we will see you up at the dyno day?

warwagon, thank for the reality check, I guess should do it up right and pull the dipstick and get the ground out. it looks a tad short anyhow, so no use taking away any slack. then its off to the chassis ground. is there any body to frame and ecm to body grounds? ( i just need to find the ground thread, then i can quit asking stupid questions. )

we have plenty of 12V cigaretter lighter plugs (old cb radios install kits, etc) I take it plug one of these male plugs in and read the voltage on the pigtails? do i need to do it running or off?

it is probably all just grounds, probably didnt get them right on the swap.



on a side note, my paranoia is taking hold. called the buddy at Delta (after I drove through the salt) and he said the storm was thurs. night/fri morning, so the most recent the salt is is friday. the road was bone dry, and the tire ruts had less salt residue, but I bet a tick of salt dust got on the truck. It will be fun scrubbing the truck in fall Idaho weather, as that is the only option! the sexy truck is the only one with this luck. only one of my trucks I hit a deer in (luckily swerved and caught is leg in the left REAR fender, so a kink in the box fenderwell lip is the only damage(long live the front end and cab!! ) but its still a bummer.) rock chips the easiest out of any of them (and of course the rock dent slightly) etc. oh well, its just iron.

finally, if a moderator wouldnt mind, the need to drive 200 miles part can be removed from the title so no one thinks the truck is stranded.

thanks for all the help guys!

 

[WarWagon]

I have grounded the ECM on the glow plug controller bolt on the 1995. Slack is just a term relevant to where you put the wire on the engine. On the huge chunk of iron isn't going to make much of a difference where it is grounded. Follow the ground wire into the harness and see if it can be grounded elsewhere on the engine.

Cig lighter plug running and measure battery voltage measured at batteries. You are looking for a difference in case the ign switch, fuses, positive cables, etc. are bad or high resistance from corrosion.

 

[jrsavoie]

I also add a ground to the battery box to make up for the cheesy ground to the inner fender. I've had a lot of those strip out.

I also add a ground from the heater blower to the dash frame, the battery to the intake studs and the battery to the frame by the starter. If the studs lose ground as sometimes happens, the 10 ga wire will supply the ground to the stud

I try to take my grounds directly from the battery after doing the Allen screw update from the factory battery bolts.

I do some of them with a single piece of 10 ga. wire with multiple eyelets crimped and soldered on.

Copper Coat on everything. While it's been noted that it doesn't test for continuity with a tester, I was told long ago that the copper helps with the conductivity in a tight connection and provides the necessary barrier to the air. It also has a higher working temp.

 

[GM Guy]

going to play with it today, and i had an idea. could it be the resistor in the PMD plug, or possible lack thereof? considering it ran great for the guy for a while, could it have possibly went past the 50th keystart and looked for a missing resistor that got lost in the swap?

 

[NVW]

IIRC Obd1 checks every 50 key cycles. TD I believe said Obd2 keeps the resistor value in memory, a dead battery may change that.

It sure wouldn't hurt to try one though.

 

[GM Guy]

fixed it. IDK what it was.

I pulled off the upper intake, and the filter harness and all related plugs had all retainer lugs and latched cut off (courtesy dumb installer, plugs didnt match, so lets hack and whack), so I ditched the filter harness, stole a rubber boot to put back on the main plug, and plugged it into the IP. zip tied it in.

I also installed my remote mount PMD kit while upper intake was off, need to bolt to bumper and zip tie harness to complete install.

now she runs fine! now to the non-operational push button 4wd, fluid level checks, and a engine and tranny oil and filter change.