Chevy 6.5 Turbo Diesel REVS Out of CONTROL?! (Part 1 - Throttle Diagnosis) 

Fuel is by-passing inside the injection pump itself . Worked a large GM dealer in Toronto , changed literally hundreds of these pumps , just get another one and don't forget new fuel filter , set TDC offset with scanner when engine is at operating temp and add Standayne fuel conditioner , yeah and move that driver module off of the pump using the resistor that came with the driver module as they were calibrated together . A higher resistor number meant more power but to the expense of fuel mileage , Aftermarket harnesses and mounting plates usually came with a number 9 resistor , high fuel consumption with those , usually had a 4 stamped on the resistor when looking inside the bottom of the the driver module wire connector . Good luck , reminds me of the good old days when life was simple .

Bought mine new in 94. Still have it. They don't take kindly to abuse and are prone to electrcal gremlins. I have a local shop that actually has a younger tech that works on these so very fortunate as they are not welcome in a lot of diesel shops. This is the first deep dive video on the electrical side of the fuel control system that I've seen. My hat is off to you and to boldly go where no one likes to any longer. Looking forward to Part 2.

This thing I love about Ivan's diagnostics is that he doesn't just sit down and Google stuff. He does a step by step process of elimination and scope wizardry to get to answers. This one's tough because you know the ecu is decades old but you don't want to condemn it right away.

Be careful on that call on the PCM. I had a 97 3500hd with 6.5 with the same issue and it was the pump. I luckily had a sister truck beside it I was able to swap the PCM and PMD due to it already being remote mounted on both trucks. I was for sure it was the PCM but to my surprise it was not. I didn’t go as far in depth on the diagnostics as you are doing so you may be more confident on your call but the truck I had surged horribly when trying to drive to the point it could not be driven and in park any touching of the throttle would send the engine to full rpm. I believe it was an issue with the fuel metering solenoid that comes in the back of the pump.

Make sure that the resistor that calibrates the pump is inside the connector of PDM's, they slide onto the pins. We were told that those were important back in the days of replacing these injection pumps under the GM special policy.

You have the patience of a saint Ivan. Amazed by your cool level head and the "let's see what we can do" attitude. Hat off to you sir.

Older guy's all retired working on these things. Ivan you will be able to retire early if you just get a few more of the old chevy 6.5's😆😆 Great work ethic as always. Have a geat summer 👍

Love the variety of vehicles. Equipment etc Ivan brings to his channel ! Keep it coming Ivan !👌

Holy highs and lows Batman. This beast needs to be soothed

Love those 6.5s the problem is the modules sitting on the engine are prone to failures like overheating the modules. That's why the RPM is ramping up. I've seen this issue before. The pump fuel is bypassing that, causing issues. Some injection pumps need to be rebuilt with upgraded parts that'll take care of the problem.

The Duramax was such an enormous step forward over this old Detroit diesel design

You give me faith Ivan! Everyday I go into work, I feel better prepared for whatever is next, and a lot of that confidence is directly from you. Never stop learning people!!!

There's your problem. A diesel with a gas pedal. 😁🤣

You did a great job of applying advanced diagnostic principles to this platform that you've never worked with before. All normal EFI control principles apply until you get into the actual DS injection pump that's its own beast.

Hi Ivan, There is a braded copper ground strap that runs from the firewall behind the exhaust downpipe from the turbo to the back of the left bank head, when it corrodes it sets up all kinds of crazy feedback to the computer behind the glovebox and the pmd, I’ve had a couple of 94’s with this problem, I went back to a 93 five speed 4x4 no computer never been a problem and still going strong,

This is the first 6.5 I've seen diagnosed using a scope. Ivan, you are a true electronic technician. Most just parts cannon these engines known by history on internet Q&A.

I had a Cutlass Supreme diesel in college. Honestly the best car I ever owned. When I moved I sold it to a friend because I needed the money. Bad move on my part. But it did act up exactly as this one. It was the injector pump. Only thing that ever went bad.

If you had a signal generator you could dial it in the correct duty cycle when the engine actually idled for that few seconds. Eliminate computer control. Not sure if that’d work but would be an experiment

I love how you talk us through your thought process. I wouldn't be ready to call the pcm just yet. Need some further data gathering.

Pretty advanced diagnostic, Ivan! And on an older school diesel! I think Paul Brown comment is hitting the problem root.

When I was in the military, serving in Japan, I worked in the heavy equipment shop, we had a detroit runaway one day. GI's scattered. It was a genuine runaway though, not just 2k rpm. I got out of the service and went into automotive and left the heavy equipment field.

Try hooking up a frequency generator up to the injector control line on the pcm that will tell you for certain if it’s a bad pcm putting out a bad signal to the IDM

Just the idea of a Diesel runaway frightens the life out of me

Fantastic video! Loved everything about it.....diagnostic skills top notch! Love your channel!

This could be worse; this engine could be a 6.2 liter diesel. I drove one on a delivery route that was a C-30 Chevrolet with a 20' box on the back. Those engines didn't have turbos and 130 horsepower wasn't enough to "pull a sitting hen off a nest." The company eventually got some 6.5 liter diesels that were somewhat trouble-prone and the 6.6 Duramax was an improvement over those engines. I am wanting to say the Duramax was an Isuzu design IIRC. I own 2 6.0 liter Ford diesels and I have a newfound respect for those upon viewing this video. Ivan, you are getting down to the nitty-gritty when it comes to waveforms; I don't think you have gotten this technical before. Good to see it. GREAT VIDEO!

This is where I'd break out my decade box. Add resistance to mimmic ambient temperature. And see it makes a difference.

Love your work Ivan! thank you for sharing your knowledge Sounds like the injection pump. Low and ultra low sulfur fuel really wears out those Stanadyne/Roosa-master pumps. I'd change the nozzles and glow plugs out too while it's apart and insist the client runs Power Service additive in every tank. Those were junk new, really junk now.

In the first test the pump command at 4k RPM is LESS than at 1k, and so is the feedback, and the solenoid is tracking the command. How could a smaller command result in more RPM? It has to be a mechanical problem. Fuel must be coming in outside of the command, or the pump is producing too much pressure, or something like that.

You've got a good one here Ivan. Looks like one of the comments had an answer for this problem.

Old Detroit two cycles had an emergency shutdown flap held open by a cam lock operated by an electrical solenoid, when they ran away (every chance they got) you could hit a switch or manually hit the cam and shut off the intake but it was scary as heck.

LOL! 10 minutes in, and best be tearing apart the engine computer and checking for bad/leaky capacitors, and corroded traces. 29 yrs old, I can guarantee there are bad capacitors! 😉

I’ve had a couple of these trucks with similar issues and they all had glow plug codes even tho the glow plug system all tested good. They all had pad PCMs

Interesting case study. I have never worked on one of these. I had a K5 Blazer with the 6.2 liter Diesel many moons ago.

Had a couple of these back in the day with same issues.seems like the pumps were over fuelling injectors.Replacing pumps and setting the TDC offset always fixed the problem

"The flying wings of Quality".... 🤣😂

I can't wait for part 2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Every trip to the Pine Hollow is an adventure, requires one to be brave, smart, resourceful, but also humble and cautious. No wonder why people drive or worse, tow there for hundreds of miles to get help.

Trying his hardest to use a 4 channel scope to identify an electrical malfunction when the problem is simply a bad injector pump. ECM is not in complete control and doesn’t know how to handle the situation. Fuel is bypassing internally. Touching the throttle commands even more fuel, hence the high revs. Rebuild or replace the injector pump. Relocate the module and put a computer fan on the heat sink.

I’ve had a few of these trucks. Does sound like the injection pump, had some good luck with Pensacola diesel reman pumps and good price. However, had an issue that took me forever to figure out similar to yours although truck would go into limp mode. Theres a harness that runs in the intake valley front to rear that goes to the pump and other sensors, mine melted together and ended up shorting the ECM as well, there are well made and insulated harnesses available. Only found it while changing the injection pump as intake has to come off but I was at my wits end and thankfully found it.

never worked on that system but .... dont worry about the temp. yeah its off but it really makes very little difference on fuel delivery except maybe on start up. it has a seperate shutdown sollenoid so if you unhook everything but that on the pump it should start at idle and run smooth. if not check for sucking air and if not sucking air and still erratic change the pump, a sticky timing advance will cause elevated idle rpm. that most likely is a stepper motor running the fuel metering controls. it is fast and precise. any binding in the mechanical side will cause what this thing is doing. you could depin the stepper and monitor the throttle circuits and output to the stepper if thats all good change the pump. the mechanical version of that pump was real finicky and does not like low sulfer diesel fuel.

GM went to an electronically controlled IP in 1994 which introduced a new level of complexity to the system compared to the mechanical pump of 1993 and older models. When they run right, they run great, but can be a pain to diagnose and repair when they act up. I have that engine in a 1992 truck with the mechanical pump and it's been pretty much trouble free.

Another variable that still remains is the coolant temperature sensor circuit. The temperature/resistance chart shows that the PCM should register -40 degrees with the sensor unplugged (maximum resistance), but your reading only went to -7 degrees. The circuit still has a problem with the sensor unplugged, and the only answer is a partial short-circuit or internal PCM problem. Wherever the problem is located, it seems logical to conclude that the fuel injection system may be affected by it as well, whether it be corrosion or a pinched/chafed harness.

Thanks Ivan!

Interesting for sure. Have to review a bit and do some more head scratching…. Never laid a hand on one of these, but what Paul said sounds pretty logical. I’ll go with that theory. 👍👍🇺🇸

I used to work on the shops old 96 chevy tow truck with the same engine. And it would sometimes cut off while coming back down to idle. Replace the injector pump driver module and it would run fine for 6 months or so. Then start doing that random stalling again. This truck already had the module relocation kit installed behind the driver side battery. So, it made swapping the module a breeze. But I suspected there was a high resistance problem in the injector pump itself. But the shop owner didn't want to replace it.

this is very interesting it’s acting like both an electrical problem but it could be a mechanical issue as well im very interested to see what you find

That thing is a Beast!

I will post more later but this is most likely a worn injection pump from the poor fuel filter I see installed. The other two causes are the PMD or lack of a calibration resistor in the PMD connector. I doubt this is the issue as he had tried so many PMDs.

"Flying wings of quality" 🤣🤣 We call them "the wings of disappointment".

Thank you PHAD

Call me crazy, but just purely as a thought experiment, I can kind of create a scenario where extra fuel bypassing in the injector pump could cause a situation like this. 2000 RPM is probably a comfortable place for this truck to live on the highway, it's a '95, and so depending on how the injector pump is designed, wear on the flow control pintle, seat or orifice could favor this RPM, and continue to bypass at higher RPMs, causing it to hit the rev limiter. Further, with these being old mechanical function design with a rudimentary ECM and some electronic controls and monitoring slapped on top, it's entirely feasible that the ECM doesn't have as much control as we're thinking it does, and instead, it's really just following basline maps for expected behavior at certain data points. As per usual, this is entirely speculation, and the only tests I can think of to alter behavior in a predictable manner are insanely dangerous on this design of diesel. About the only "safe" thing I can think of is a thick piece of steel to partially block off the intake and a 5-gas analyzer to look at combustion and fuel mixtures. Even then, without a known good, I have no idea what I would do with this data. Man, this is a really good one!

Ince in a truck shop I watched an 84 year old man in a wheelchair telling s younger tech what to do, after chatting with them, they told me that they got an old suv, 1985 ford, new guy had no idea what he was doing, and old fella on his pension, was begged to come and assist.

To continue on the injector closure time PID on these early truck is misleading. It is actually the fuel solenoid closure time. Just like a gasoline injector hump, this is measuring the time it takes for the solenoid to close and start injection. That is why the value does not change much with RPM or load. It is not the on time of the solenoid. In your waveform if you measure the difference between the command red signal and closure signal green, you will get the same reading that the PID displays. Also if you look at the scan data you will notice the shutoff solenoid will be activated to bring the RPMs down. Anything is possible but I have yet to see a PCM cause this fault. The introduction of the black plastic fuel filter ended up destroying these pumps. Stock filtration is 5 micron and the black plastic one is closer to 20 micron absolute. 5-7 micron particles cause the majority of damage to a diesel fuel system.

Good morning Ivan, another mystery one with the parts cannon. I am very suspicious of the PDM relocation wiring.

I had a similar issue with a duramax, i replaced the cam and crank sensor and no more issues after that.

Last time I fixed one of these it was the pmd extension wire harness and it rubbed through

I know this is s diesel but I owned a 1997 Chevy Monte Carlo Z34 that did this same thing . No one could figure it out at GM dealer . Finally I closely checked the MAF it had a cracked wire that would intermittently do this same symptom you are having because the heater wire would intermittently make contact and drive the computer nuts.

These are notorious for bad pumps and it could be an ECM but I'm thinking there's something broken in the pump

This is why I LOVE my 1995 Ford F250 4x4 with a 5.8l ALL PRIMITIVE PETE, cabled throttle, crank windows, no cruise control, manual transfer case, manual hubs and only electronics is fuel injection and transmission which I can deal with that!!!!

A bad input to a computer gives a bad output. On a Powerstroke, the IPR (Injector Pressure Regulator) (a fuel pressure sensor) output (like gasoline engine MAP) tells the computer how much energy is going into the engine. If that signal is indicating low, the computer will over command for the desired result. Possibly a bad pressure sensor regulator on the Duramax causing bad commands. The 7.3 PS goes dragster crazy when the IPR fails indicating low fuel rail pressure. Scary to drive it because accelerator pedal becomes hyper sensitive.

Cars of that age might have electric problems due to leaking capacitors in devices (ECU, ) Anyway i see more good comments here, follow them you will succeed i am convinced you fix this one Ivan

We had pallets filled with old 6.5 pumps. Nobody wanted them for cores, sent all to scrap.

I would do a TDC offset learn and then see what it reads. If someone moved the pump and did not do this it wont change the reading in scan data. It will look in spec but its not. If its + or - 2.46 it needs to be timed. I always found -2.38 to be the sweet spot but hard to hit.

Wow Ivan! That must have been a big Hammer that you hit your thumb with! Ouch

Thanks!

Yeah getting a quality part these days is brutal,, recently my 2002 F250 power stroke accelerator pedal was acting up and I thought no problem I'll get a Motorcraft,, well no,,, it doesn't exist.. Apparently for about 20 months between 2002 and the 2003 change over to the 6.0 was the only period that used that particular accelerator pedal and it's only available in the aftermarket.. Fortunately the one I got works fine... So far......

Drain the water out of the engine mounted fuel filter through the petcock mounted on the front of engine. Take filter out and check bottom of filter for sediment

You bashed that finger really good

What color smoke comes out when loping. Got to have accurate water temp sensor and all glow plugs must working and in control

since the old pdm is still on the pump it is likely they didn't transfer the resistor to the new pdm. This will cause the exact problem, just look into the plug on the pdm to see if it's in there.

Leaking capacitors in the PCM corroded several PCB traces causing the erratic operation...

If it were a mechanical pump, I'd think it was a sticky governor, or a restricted vent on a diaphragm damper. Could pump solenoid spring be be broken or the armature crudded up?

That loping idle reminds me of a Honda with a bad idle air valve.

I have had to deal this problem about four or five times on the 65 Detroit diesels. 90% of the time it is ECM. But there is one odd time. That the old PMD went crazy and cause it to fry the ECU. But that was one time of multiple trucks I have had this problem with. Also too make sure that it's the PMD has a calibration resistor right into the pigtail there are resistors you can get from 1 to 10 5 and 7 limit the max fuel rate. If you don't you can be shooting excessive fuel into it it's not much of a problem you can get them from Rally's from dorman for like 35 bucks.

The Flying Wings of Despair!

My guess on the fuel rate being 0 is the pcm is trying to drop the rpm, but with the injection pump bypassing it can't.

I was about to say idle air control valve, vacuum leak, but diesel may different.

Fuel supply to solenoid OK? How does it measure fuel output? Is the output measure part of the control loop?

It sounds like brothers Subaru Forester when it had an air leak at the throttle body & it was fitted with a MAP sensor like that 6.5 litre diesel V8 engine is. I don't think that it would be the PROM inside of the ECU that's at fault unless someone has mucked around with it !

Our 1980 Cutlass Supreme Diesel never had such problems, just blown head gaskets!

Fuel pump, fuel injectors, fuel filter, blow out the fuel line to tank, wiring harness extension, PCM, wiring harness. Has he been running any performance chips? Looking forward to this one.

Remove the feedback line, it is oscillating, that is mean the feed back is wrong, the computer is good. It is a mechanical problem for sure.

These 6.5 diesels have the PDM installed in the wrong location where there is a lot of heat. There are aftermarket PEM suppliers that make a better unit and it needs to be relocated to a cool spot. Good engines but faulty electronics.

My now brother-in-law had one of these when we were in college so I got to learn a little more about them. I remember the 3 potentiometers in the throttle pedal. I think you need to compare PCM output to a known good. If it's commanding a fuel solenoid duty equivalent to 2000 rpm when it should be idling, that suggests a PCM problem. Also have to check the feedback because I presume it uses the feedback to modify its output to achieve the desired fuel quantity.

The first part of the video i was thinking a clogged fuel filter or bad fuel filter. along the way i'm guessing a pump not timed correctly or out of time

Ivan every time I see that left thumb nail…boy I cringe!! Been there done that many times.

Intermission,,, where's my popcorn !

18:38: REV LIMITER!🤣🤣🤣

If it's mechanical Injection is it a balance point system, incorrect balance point can definitely cause a lope at idle

This machine is 'possessed' too!

Can't help but think that there is a strange history for this truck that the owner isn't telling you about. I think somebody threw some bad or incompatible parts in the engine that is confusing the ECM and causing the idle to go crazy.

Notice : guages stay up with the key off ? Powers and grounds?

would be helpful for a shop declining a problem to suggest one that will. Doesn't mean the 2nd shop is better than first or first worse than second but that a foot doctor doesn't do nose and mouth work.

Interesting how it can be both 1800revs and 700 revs at the exact amount of PDM duty cycle but at the same time timing of those pulses relative to CKP is different quite a bit. So PCM can make it idle if it wants, maybe mechanical timing of fuel pump itself is not correct?

I’ve done ton of these things and 90% of where the wiring harness is shorted underneath the fuel filter runs along the valley of the engine fuel disintegrates the installation on the wiring, major problems and they will do all kinds of crazy things

18:37 i think that was the rev limit , and the tach was bouncing for sure

what was added to cause this problem, possible miswired harness , other common problems cracked intake,cracked hose, water in fuel

Boy you sure did a number on that thumb….ouch!

Yup !injection pump is failed leak inside the pump .

I wonder why it showed -7 with unplugged coolant sensor, isn't it supposed to show - 40?