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RPM jump with light touch on throttle.

jimloycom

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Cranks instanly, runs like a beast. Issue is it has no throttle responce. It is like 2-3k rpm with barley a touch. New IP, acceleratpor pedal, new PCM.

- What were you doing when it happened? Normal driving
- How was the truck running fine before this problem appeared? fine
- Has this problem ever happened before? No, new issue
- Describe any related factors that might be part of the problem. Just started getting bad. Replaced accel pedel.
- Have you checked for DTC (Diagnostic Trouble Codes)? (Y.N)y PCM short
Diagnostics:
1] Starting:
1a] Does the engine start? y
1b] Does the engine crank over? y
1c] Are your batteries fully charged? y
1d] Have you removed, cleaned, and tightened all battery connections? y
1e] Does your Wait to Start light come on for a time? How long? n
1f] Does your glow plug light come on? y For how long? 15s
1g] Do you see smoke from the exhaust while cranking? What color? n
1h] Does the Service Engine Light Glow during Start/bulb check? y
2] Fuel Issues (if not running):
2a] Can you hear your lift pump working? Y, electric by passed
2b] Do you get a steady flow of fuel from the water drain (T-handle) ? y
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? y
2d] Loosen an injector line and crank the engine - does fuel come out? y
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? y
3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) remote
3b] Condition of Extension harness (if used) Vendor or Homemade? Exten/homemade
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. good
3d] PMD Make: D-tech
3e] PMD Age: 6mth
4] Stalling Issues
4a] Do you experience stalling only when hot? n
4b] Does it stall under particular circumstances? (ie hit bump, or on accel) n
4c] Does pouring cool water over the IP seem to help with restarting? n
4d] Is stalling momentary (engine recovers)? n
4e] Does SES light come on when engine hiccups? n
4f] Does cruise control quit working when engine hiccups? n
4g] Does re-starting seem to reset engine, restoring cruise and power? n
4h] Changes to dash lights or instruments during stalling events? n
5] Running Issues
5a] On cold start, does upper rad hose get hard before engine warms up? n
5b] Any bubbles or oil film in coolant overflow tank? n
5c] Any white slime on oil surfaces (dipstick, CDR, oil Fill cap)? n
5d] Excessive white smoke from exhaust on cold start? n
5e] Excessive black smoke from exhaust under hard acceleration? n
6] Performance Issues
6a] Do you have gauges (boost, EGT) ? n
6b] Maximum boost under load? n
6c] Have you added a performance PCM (reflash) or Chip? n
6d] Have you changed exhaust / downpipe / crossover? n
6e] Wastegate – mechanical or vacuum (OEM)? V oem
7] Temperature-related Issues:
7a] Single or dual thermostats? Not sure
7b] Have you replaced them lately? Manufacturer of replacements? n
7c] Have you pulled and cleaned Radiator and coolers lately? n
7d] Have you replaced the fan clutch? Manufacturer of replacement? n
7e] (winter) Have you tested your antifreeze? Good to what temp? n
7f] (winter) Are you using a winter grille cover? n
 
Welcome Could you take a minuite to fill out your signature so we know what it is you are working on. On the top of the page click on userCP. a drop down menu will come down click on edit signature then just fill in the details of your truck.
If you are getting a pcm shorted code you are probbly in back-up fuel mode.It cuts the fuel way back to limp home. A fried ecm/pcm will do all kinds of weird things. I had a 3month old remaned ecm go bad and I couldn't time the ip and tranny was acting up too.
Before condeming the ecm you will need to check all the wires coming in and out of it for bare spots and shorting. Also check all connectors for bent or pushed out pins. I checked all the wires with a ohm meter[a real pia] What was the exact code? Did you try clearing the code? The reason I ask is that if it is a 5volt reference shorted it would be in one of the sensors.
If you are getting much vacume in the fuel tank your fuel cap needs cleaning or replacement with a "Diesel fuel only" cap. A gasser cap is wrong for these.
 
Did you replace the IP, PCM and pedal for this problem? Is this a 94 truck?

Just need to do some diagnostics, which could take maybe an hour of your time.

You have code 54? There must be other codes too then?

15 seconds is a long glow time, either its really cold there, you have a custom PCM chip, or your 5V signal is being shorted to ground and both the Coolant Temp Sensor and Intake Air Temp sensor arent returning a voltage so the truck thinks its really cold. There are a slew of other things that will happen to cause the truck to run this way, including losing your crank position sensor signal, so it goes to backup fuel mode which sets a constant fuel pulse width, fast idle and poor performance.
 
Limp mode-It's not running in Limp mode it is running it attack mode.. It's wants to go.
Cleared code-I tried clearing it by removing the battery leads.-no help.
New Stuff-Reman IP from KR services,Bullet proof PMD
Glow plugs on cold day maybe 10-15.. That is a good clue. It does seem to think it is cold and sometimes idles up to 2kRPM.
5v-I checked the voltage on the paper clip area and it was good.
Crank position sensor signal-I thought if you lost this you loose rpm reading?
I really appreciate this site and that you all are takng the time to help me!! This is really nice. Any thoughts on this subject is greatly appreciated!
 
Try unplugging the coolant temp sensor on the coolant crossover passenger side. By unplugging it the ecm will think it's -40. That will advance the timing and speed up the idle. If you have no change the temp sensor could be bad. The temp sensor can be tested with a ohm meter. There may be the resistance table in the reference library. I've got it some where but have to dig to find it.
The rpm reading on the tach in the dash gets it's signal from the alternater.
 
I unplugged it and had no difference. I ordered a replacement pmd.
The other code was something to do with the torqe converter. Ill report the exact number when I get home.
There is only 2 codes
Truck has just got more and more sensitive over time to the throttle pedal. For a long time is was driveable. Now it is on 2-3 k rpm with the slightest touch. if you have other thoughts please post. Hopefully pmd. If not may do a ip. Hate to.
 
Well the 5V is not the DLC connector. Post the actual codes.

To clear codes you need to use the pedals, not the battery removal. With paperclip jumpered A to B on the DLC, turn IGN on, depress both pedals to the floor for 20 seconds, release pedals, turn IGN off. And remove jumper.

However, whenever you tun IGN on it will sense a short if its there, so you will always have a returning code upon turning on IGN.

The 5V goes out to all the sensors. Crank, Intake Air Temp, Coolant Temp, IP Optical, Accelerator....etc... And there are different 5V rails in the PCM so one doesnt affect the others always.

You need to get schematics and a multimeter, not swapping parts.

The tach in the dash runs off the alternator, not the crank sensor. A scanner might also be able to point you in the right direction by observing abnormal sensor readings.

Rather than just unplugging the CTS on the T-stat xover, also unplug the Intake Air Temp (IAT) sensor on the intake manifold. Both are just two wires. Then on each harness jumper the two pins in each together with a paperclip (jumpering the two wires, not the sensor itself). That should make the truck think the temperature is really hot and not be in fast idle, and very short to no glow time (less than 1 second). If you still get a long glow time and fast idle then the 5V going to those sensors is shorting to ground, instead of making it back to the PCM input.

Limp mode is not necessarily sluggish at idle, it just doesnt run at high RPM well. It sets fast idle and a longer pulse width so more fuel input at idle to make sure it stays running.
 
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I unplugged it and had no difference. I ordered a replacement pmd.
The other code was something to do with the torqe converter. Ill report the exact number when I get home.
There is only 2 codes
Truck has just got more and more sensitive over time to the throttle pedal. For a long time is was driveable. Now it is on 2-3 k rpm with the slightest touch. if you have other thoughts please post. Hopefully pmd. If not may do a ip. Hate to.
Whyreplace pmd? No symtom of that being bad. Same with IP. As Buddy said, Throwing parts at it isn't going to fix it unless you get real lucky before you go broke.
A Tech 1 or Tech2 scantool or GMTDscantech software[only things that work properly on a 94-95 6.5] can at least point you in what direction to go. Without knowing what the sensors are reading it is mostly guesswork.
 
You all have more faith in me than I do. I will reset the codes and try some of the recomended test this eveing or tommorw. I'll get the exact codes and post them. I agree its not smart to throw parts at it. The place I bought the PMD is sending out one no charge, just have to send one back. So that's just a freebee. I'll check into the scanners also. I can't say enough of how appredciative I am to have some mechanics looking over my shoulders!
 
Throwing parts at them is what the stealer[dealer] does best. Here , we try to help diagnose the problem. Far too many of us has been robbed by a parts replacer,stealer or other. Most of us aren't "mechanics" but rather, do it your selfers with some knowlage and experience. This forum is about sharing and helping with some humor thrown in.
 
How long ago(miles) was the IP replaced? Where did you get it?

It also sounds like a severe Optic Bump, I'm just wondering if the OS wasn't tightened down and it slipped. An idle fuel rate reading would help rule that out.
 
The other code was 67 Torque Converter Clutch (TCC) Solenoid Circuit Fault
I plan on working on the truck today. I should have more info today. The IP was purchased 1-17-2010 from kr services. DS4831-5521
 
Here is what happened today. Tried shorting the CTS and IAT. The glow plugs were maybe 3-5 seconds. Beside that change the rpm issue has not changed. It is currently reving up to 2k sitting in neautral. The new PMD came in, no change. So I'm getting low glow plug time and fast idle, so that means the 5v is getting back to the pcm?

I'm considering buying the GMTDscan tech tool. Can this tool possibly adjust the issue out? Or will it just give me more information on the issue? I have unplugged the ECM and reseated the connections with no luck. Did the cable wiggle test-found no diffrernce when it was running.

Scan tool? More test? IP now? Any thoughts?
 
GMTD scantech is a great software package. A real bargain. It won't adjust your problem away. It will give you lots of information and the ability to set the timing and top dead center offset learn. If you have a laptop computer with windows XP or Vista it will work. It will only work on 94 and 95 gm 6.5 diesels. Nothing else. It also won't scan the ABS brake system. Almost all the features of a $4000 Tech2 at $200 something. That is less than the diagnostic fee at some dealers.
With a scan tool or gmtdscan tech you can command engine speed. If it won;t respond to that chances are getting better it could be a internal ip problem. Gotta get back to work
 
Do you have the DTC57 with the DTC67?

You should not have a DTC67, theoretically, unless your truck was modified with a turbo, because that DTC should be unique to the 4L60E transmission that came with the 94 1/2 ton Naturally Aspirated engines.

A 6.5 turbo truck should have the 4L80E.

Did this truck all of a sudden start performing like this or did you get it this way? Did someone swap out the PCM? If so they may have put the wrong EPROM in it, and this is causing your problem. You may have an EPROM/chip for a N/A truck. Just pop off the glove compartment, pull the PCM out, open the little panel on the back of it and let me know the 4 letter code on the chip. Like BLRM or something like that. I will check which truck it is for.
 
I ordered the scan tool. Looking foward to using it.

The Chip is BPDN 16217518
It has been great for a while. Just started getting less and less throttle control.
If it was modified it was the previous owner. I have no idea on that.
Yes I have DTC57 with the DTC67.
 
You'll love having the scanner... Exciting stuff at first, then great to have that type of diagnostic power whenever you need it, with all the time in the world to 'think' about things while watching the engine warm up...
 
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