New-to-me 1993 K3500 issues.

[BrIONwoshMunky]

Hey all, I've been lurking and reading and hoping maybe someone on here would have a couple of answers for me.

My truck is a '93 K3500, 6.2L, NV4500, C&C truck with an aftermarket flat-bed.

Would all of these symptoms be commensurate with a fried brainbox/ECM (If I'm correct in assuming it stands for Engine Control Module) or whatever due to welding on my bed... with the batteries installed... which I just read is a no-no. Also, does my truck even HAVE an ECM. I'm assuming it does, and is attached to the Hydroboost/Master cylinder.

1. Speedo intermitently drops out while driving down the road. Drops 5-10 mph, back up, down up down... ect for a few seconds, then seems all right

2. I think my ABS (if there is any ABS) activates while going down the road. I hear a clicking from the lower dash and if I put my foot on the brake, I can feel the pedal pulse. Happens every so often... again for just a few seconds at a time

3. I replaced the temperature sensor after testing the guage by grounding it out and having the dash guage peg out. Now, with the new sensor, the readings are way low, like not even one tick on the dash guage.

Are brainboxes/ECM? engine/model/year specific or can I pick up one and plug in and go?

Thanks in advance!

[DmaxMaverick]

Welcome aboard!

Your truck has an "ECM" (emission control module, in this case), but the truck will run just fine without it, and it won't cause the issues you are seeing.

It sounds like you may have a ground issue with the IPC (Instrument Panel Cluster) and perhaps other areas. Welding may or may not have a hand in the problem, as this happens on trucks never welded. Since replacing the temp sensor changed the condition of the temp gage operation, it is most likely a wiring issue (ground, connector, or chafed wire).

The ABS activation is probably related to the speedo errors. Your truck may have RWAL (Rear Wheel Anti-Lock), vs. actual ABS, and it's sole input is the VSSB (Vehicle Speed Sensor Buffer) or the speed sensor. On 4x4's, this usually indicates a failing transfer case (metal shavings interfering with the sensor), or a sensor/VSSB failure or poor connection. Check your front hubs. If it has a wire going to each, you have ABS. If no wire (to the wheel speed sensor), you have RWAL. If you have cruise control and it drops out with the speedo, this problem isn't the IPC.

It could also be a problem with the ignition switch. If you notice other issues with accessories or unexplained stalls, have a closer look at the switch.

In any case, verify all of your grounds are clean and tight.

[JohnC]

No emission controls on the '93 6.5's

The box on the booster is probably the ABS. Only acts on the rear axle, as Dmax said. It is not wheel independent, either, so the speedo issue is likely related.

[BrIONwoshMunky]

Thanks for the replies guys! I probably should've manned up and asked sooner, instead of beating my head against the wall and staring at stuff like it was going to magically fix itself.

My engine is a 6.2L, not a 6.5L, but I don't think it has any emissions control, at least according to the sticker on the air filter housing. The truck has no front wheel ABS, so I guess it's RWAL. Also, there's no cruise control, and the engine never cuts out or stumbles once it's warmed up. It hiccups, coughs, and belches some white smoke on cool/cold startup, but clears up in about 30 seconds, reading on the forums has led me to believe my HPCA/fast idle solenoid may need some tweaking/testing, along with confirming the glows operating properly.


Would I be correct in assuming the VSSB is a 2-wire connection sensor somewhere on the transfer case, and that faulty inputs (whether from a chaffed/shorted wire, or from a shavings contaminated transfer case) from this are causing the RWAL to think the rear driveline is stopping when the speedo bobbles around?

If memory serves, while greasing the driveline, I had seen some chaffed wires from a 2-wire harness located atop the front driveshaft, near the transfer case shift linkage under the cab,that appeared to be coming from the transfer case.

If shavings are interfering with the VSSB, is a simple flush/refill of the transfer case ATF called for? It doesn't grind, whine, or make any other noise while in 4x4 mode, and shifts into all positions (4L, N, 2H, 4H) easily with a good positive lock-up feel.

And, would there be a common ground on/for the IPC that I could check.

This has all been an adventure so far, and these forums have REALLY helped make sense of it all.

Thanks in advance yet again!

[DmaxMaverick]

Correct. No emissions, to speak of, on the 93 HD models. It should, however, still have an ECM (ECU, on the drawing, IIRC). Only the 3500HD and Workhorse chassis had no ECM in 1993. The Cab/Chassis may be among them, but I can't find any info to confirm that. Some government and fleet trucks (utility/RR) were also EPA exempt. These were required by the EPA since January, 1987, on all vehicles with a GVWR less than 12K. Federal emissions truck ECM's are passive, meaning they only store parameters of the systems. In most cases, you won't notice if it fails.

The VSSB is under the dash. The speed sensor is on the transfer case, rear shell. The forward connector goes to the engagement indicator (makes your 4x4 light come on, and completes the circuit to the front axle lock).

If the VSS is fouled in the transfer case, a drain/fill will only replace contaminated oil with fresh oil, but does not fix the reason for the contamination. There is only metal and plastic (rear pump housing, seal cups, shift fork pads) in the TC, so if it's fouling the VSS, it's getting ready to leave you. Do a service on the TC, and note the contents of the waste oil (Dexron III ATF). If it's dark and/or sparkled with shiny stuff, the TC is toast. Run a magnet through the waste oil after it's had an hour to settle, undisturbed. Any more than the slightest bit of very fine dust (fine/pasty residue on the magnet), it is failing. Early rebuilds are much less expensive than total failures (usually bearings and seals fixes it). If you drain anything other than ATF, it was improperly serviced (with gear lube), and is probably toast, or on the way out.

[BrIONwoshMunky]

Thanks Dmax!

I'm in the middle of working 7 - 12's, so I won't be able to get under the hood for a few days. I'll post back with updates of success or failure!

[Robyn]

I agree on the ground issues or wiring connections causing the ABS anomalies.

The caughing and smoking when cold could be related to glow plugs, but more likely is realted to a worn out set of injectors.

As the injectors wear out the POP pressure (when the open) drops off and with this goes the nice fine mist of fuel.

Slobbering "Peeing" injectors on a cold engine lead to a lot of smoke, harder starts and and poor fuel mileage too.

The glow plugs/after glow cycle can be partially to blame too, but a higher mile rig will usually have injector issues.

Missy

[BrIONwoshMunky]

I agree on the ground issues or wiring connections causing the ABS anomalies.

The caughing and smoking when cold could be related to glow plugs, but more likely is realted to a worn out set of injectors.

Missy

Thanks Missy, nice to see some consensus before I start tearing into things all willy nilly without knowing what problems to look for first.

The truck has 175k+ on the odometer, I'm sure it's a bit tired! Getting all the bits and bobs going so I can hopefully use it as a 4x4 to get to work on snow days (assuming it starts cold), and MAYBE ocassionally pulling a light stock trailer every few months.

I got it cheap enough, for sure and for certain.

Everyone talks about how underpowered the 6.2's are, but I'm used to driving a 2.3L Ford Ranger that came off the line with 105HP. Needless to say, I'm used to underpowered!

[BrIONwoshMunky]

Okay, so I haven't had/made time to check the speedo wires. I did, however, take the dash apart and didn't find anything visibly amiss other than some missing screws that hold the instrument panel in. I went ahead and cleaned all the electrical connections with DeoxIT which is an electrical connection cleaner and lube.

I then thought I'd address the cooling/temperature reading issue, and went ahead and replaced the thermostat. I bought a 180 degree thermostat and put it in. The temp gauge reads a few minutes after startup now instead of after about 30 minutes of driving. I think the coolant temp sensor was going bad, but was also coupled with a thermostat that was stuck open. It may be in my head, but I think it's running a bit better now too. This, however, brings up a new question though. After trying to decipher the gauge readings, I have come to the conclusion that I have no firm idea of what I'm seeing.

What sort of temperature increments are represented by the dash gauge? I don't think it has 110 degrees on the left hand side, and just 50 on the right. I'm thinking they may be 10 degree tick marks with the bold line in the middle left (1/4 full) representing 190?

[BrIONwoshMunky]

Once the temperature dropped, I was having cut-out/ fuel-starved issues that I traced to a dead lift pump. After snagging one from e-bay and installing it, I think I've got a new truck! I suspect that it's been dead ever since I rescued the truck from the barn lot it was sitting in for two years. I also installed a set of quickheat plugs from KD that went in without issues, (thanks to the air ratchet here at work allowing me access without needing movement for wrench operation) even though I removed 9G plugs, they probably weren't bad, but obviously weren't new.

Overall, I'm having a bit of fun wrenching on my clatterbox, and really enjoy the reading on these forums!

Just have yet another quick question that hopefully someone can help with.

Will Kennedy Diesel's 6.5TD Lift Pump harness fit on my truck? From the picture, it looks like a simple plug-and-go setup, but I'm not certain it will fit my rig.

I haven't called John yet because I didn't wake up early enough for a couple of days! I work nights and by the time I remember to do something it's usually midnight or later! That's okay for internet work, but not so much for person-to-person phone calls.

Thanks in advance!

[Inspector]

One other item that should be checked. The speedo gets it's signal from the output shaft sensor on the tail shaft of the transmission or in the 4x4 case, the back case of the transfer case. If that signal is intermittent, the cruise will drop out, the speedo will loose indication and it will affect the RWAL. Tell me I'm wrong I can take it.
I had this identical power train in a 93 but with a gear vendor under/overdrive and that sensor went intermittent. The gear vendor shifted from OD to direct back to O/D in quick succession before I could push the red button. I was in cruise, O/D and doing 55. It could give you whiplash not to mention that the damage it did to the transfer case and output shaft of the transmission that showed up a few thousand miles later. I replaced that sensor and not another problem. The sensor is a hall effect type and is relocated to the tail shaft of the gear vendor if it is installed. Grounds are good place to start though.
Just saying.

[BrIONwoshMunky]

There's probably still an issue with the speed sensor, but i haven't yet looked into it. I've got a manual transmission, so I don't really have to worry about the transmission slam shifting of it's own accord.

The potential problems that could be affecting it according to Dmax are reason enough to get it looked into when I've got the shop space to allow for enough down-time to get it taken out/repaired/replaced. Currently, I'm having to steal shop-floor space here at work for a few hours at a time. Being a noob mechanic, I don't think I can pre-order all the parts that it would probably take to refresh the transfer case. I'm afraid it'll have to wait until I get a shop built at home.

I don't plan on putting a bajillion miles on it between now and then, just some daily work runs (22mi round trip) to keep everything operating, and fixing a few bits along the way.

[Inspector]

It wasn't the manual transmission slamming but the Gear Vendor loosing the speed signal that made it quickly shift back and forth. Correctly you won't have that problem but the other things that are going on may be due to the lose of signal.
Denny

[Inspector]

Did you get it figured out?

[BrIONwoshMunky]

Unfortunately, no. Some other gremlins popped up, and took priority over the speedo. Right now, I'm dealing with a leaky filter housing. The speedo is still on the list, but seems to not being acting as wonky as it was originally. A lot of things that were acting weird at first don't seem to be happening as regularly.

The truck had been sitting for over a year when I got a hold of it, so I think some things just need to 'fix' themselves, or at least, that's what I'm telling myself.

My other vehicle had sat for a long time before I bought it as well. It had a weird habit of randomly turning on the windshield wipers while driving down the road on a sunny day. It doesn't do that anymore, and I never got around to doing anything about it. Both vehicles weren't parked because they were broke, just simply because the previous owners had moved on to something shinier.

As time and space allow, I'll get into the t-case and perhaps the front diff as well.