Well, glad you fixed it.

As I said in the other thread, we have not joined the psychic network yet. So we just go by your description. At the end, it is your responsibility to fix the truck.

Cheers!!!

 

JMJ,

I do not think you could have said it better but I also do not think that every culprit of failing IP symptoms are just that and everyone should not directly point to a bad IP.

I even went as far as to replace a brand new PMD with a known working PMD to see if this could be the culprit.

Either way, I appreiate the help of this forum. My problem has been solved by replacing the APP and I can now focus on other issues with the truck. Like my new leaking tranny pan.....

 

I am glad to hear you found the problem. Nice work!!! The APP is not a common problem with these trucks.

As difficult as it is to explain a problem through words, try to diagnose it or explain a how to trouble shoot it!!!

 

Midnightrumbler, I have a suggestion for positive contribution to the forum.

Why don't you write/summarize the symptoms and how you found out the APP is bad? Instead of cursing us not knowing about it.

I know I want to know it before it happens to me.

Who knows if it is good, may be the mods can put it in the FAQ.

 

.................

Midnightrumbler, I have a suggestion for positive contribution to the forum.

Why don't you write/summarize the symptoms and how you found out the APP is bad? Instead of cursing us not knowing about it............

good response JMJNet.
what i had wrote last night, but deleted, wasn't quite so nice.
glad it's working midnightrumbler..................

 

JMJ,

I appologize if you assume I am cursing you or other individuals as this is not my intent and sometimes words can be misinterpreted through the internet.

I am quite simply trying to make note that although 98% of individuals pointed to a faulty IP, it is directly related to the individual whom owns the vehicle to take matters into their own hands and diagnose these issues with the help of individuals from this forum and not take exact information from others and use these as determining factors.

It is good to have threads like this and others as some problems are very similar to others as these 6.5's have been around for quite some time now and 6.5 owners should have very similar fault related issues.

I am hoping that with a few searches and good luck, other individuals whom have had or are having the same issues as I, do not point the finger directly to the point and take the proper steps to diagnose the main cause of the problem. It is very easy to suggest an IP is faulty as these were symptoms I was receiving but I also did not want to rule out other factors.

Be very persistent with what you do and the pay off will benefit you and your wallet in the long haul.

Again, Thank you to this forum for your help in my related issues as this has been the biggest pain in my azz with the truck yet. I am glad I have this issue figured out.


For those of you whom have no idea what I am refering to. Take a moment and read.

Here were the symptoms I was getting with the truck.

1995 Chev Silverado 6.5 TD Ext. Cab Long Box Dually 4X4

The truck would start and idle great. I would get up to 60-80km/h and the truck would start to buck or hesitate as if I had air or lack of fuel in the lines. Going up grades would be fine but running on straights or down grades I would get the bucking hesitation. I set a DTC-25 which lead me into the APP but I also reveived a DTC-35 shortly after which made me and others believe it could be the IP. I wanted to start with the easy things before working into an IP.

I tested fuel pressure at the WIF drain at idle and while driving and the numbers were well within spec which informed me the Lift Pump and OPS were functioning properly. The fuel pressure did not drop off while the truck would buck or hesitate.

Numbers at WIF Drain Valve within Spec

I am seeing 6-7 psi at idle and 2-3 psi at hard acceleration. When the jerking sensation occurs, it did not effect the fuel pressure.


The PMD was new when I bought the truck but was installed on the IP. I wanted to relocate the PMD to the front bumper of the vehicle to rule this out as a possible factor as the truck would not buck or hesitate right away so I thought maybe the PMD was heating up and causing the issue.

The OPS was also new when I bought the truck but also wanted to relocate this for reliability. I installed an 8" grease line to the bac of the motor where the OPS original was and mounted the OPS to the fuel management unit and installed a relay with this to take the load off the OPS.

The truck has 336,000 km's on the dial so I wanted to replace all fuel lines as they appeard to be original and I put in a new fuel filter and air filter. All grounds, and I mean ALL grounds were thouroughly cleaned. Removed the Fuel Filter Management Unit and thouroughly cleaned this out as there was a slight blockage in the feed line and alot of debris on the bottom of the unit. Cleaned the CDR with a little fuel and also installed a High Idle Switch. I also installed a fuel additive directly into the Fuel Filter Management Unit as well as 2-Stroke oil to help lubricate the pump.

I was also having an issue with lack of power and black smoke so wanted to rule this out. Ended up i had a faulty Wastegate Selonoid so I bypassed vacuum and installed a home made TurboMaster and a Boost Gauge. Do not run without a Boost Gauge.

Want to install a TurboMaster?

http://www.dieselplace.com/forum/showthread.php?p=2322951#post2322951


Much to my surprise none of this helped the issue at all


Installed a High Idle Switch.....

The thing I found odd is I could not hold rpm's at all with the fuel pedal and yet with the High Idle Switch the truck held 1250 rpm's no problem. This lead me to believe I may have a faulty APP as if it were the IP, the high idle mod should also have issues holding rpm's, or atleast we would think.

I would recomened if you are having similar issues, install a high idle mod and see if rpm's can be held

Installation of OBD-I High Idle Mod

http://www.dieselplace.com/forum/showthread.php?t=340699


Want to pull your codes on an OBD-I ?.

Paper clip on the A-B connectors of the Diagnostic port - Two upper right connectors are the A -B. Put a paper clip in A and lead the other end into B

Put the key in the ignition but do not crank the motor. Check engine light will flash

1-2 1-2 1-2 means 12 which is no codes any other codes will flash as to what they are indicating 2-2 2-2 2-2 means 22 etc.

All codes will flash 3 times. If you have never done this before, have a pen and paper handy, you may have lots of stored codes but generally they reset after 50 key on engine off procedures.

You can clear the codes by either disconnecting the batteries for a short period (10 minutes) or leave the paper clip in A-B ports of the diagnostic and simoutaneously press the brake and fuel pedal 4-6 times. This will clear all codes.

Do not remove the paper clip with the key in the on position. Take the key out of the ignition and remove the paper clip. this prevents any shorting to the PCM.



APP Voltage Signal & Reference Numbers

1995 Silverado 6.5 TD 4X4 ext.cab Dually

My original APP Signal/Reference

KEY ON ENGINE OFF

Terminals G and A have 5.03 Volts and do not fluctuate at all when pedal is at WOT

Terminals D and B have 5.03 Volts and do not fluctuate at all when pedal is at WOT

Terminals E and J have 4.90 Volts and can drop down in volts to 0.64 when pedal is at WOT

Between terminals F and A have 0.66 volts and increase to 3.44 volts

Between terminals C and B have 4.40 volts and decrease to 1.72 volts

Between terminals K and J have 3.38 volts and decrease ro 0.62 volts


So we know that the APP has 3 sensors, my readings throughout APP sensor 1 and 2 appear to be correct, it is APP sensor 3 where the problem seems to be but I am not sure if it is the pedal or the wiring

Incase some are wondering what signal wirings are what

G, F and A are all in Sensor circuit 1

D, B and C are all in Sensor circuit 2

E, J and K are all in Sensor circuit 3


EXACT APP TESTING VOLTAGE

APP Sensor Circuit 1 produces a varying voltage of between 0.35volts-0.95volts dc at idle and 4.0 volts dc at WOT

APP Sensor Circuit 2 produces a varying voltage of between 4.5 volts dc at idle and 1.0volts dc at WOT

APP Sensor Circuit 3 produces a varying voltage of between 4.1 volts dc at idle and 2.5 volts dc WOT


If I compare the information based on the above readings to what I have recorded, I think we have diagnosed a faulty APP as the readings in APP Sensor Circuit 3 are way out. APP Sensor Circuit 1 and 2 are within specs....


ANOTHER METHOD of testing the APP - Very similar to above

http://www.dieselplace.com/forum/attachment.php?attachmentid=102560&d=1272309290



Again, I want to thank everyone for helping me diagnose the issues. I could not have done it without the help of this forum. All links I have included are courtesy of other members from this forum and I take no credit for these. The links and information I have included are what helped me along with the truck and diagnose the issue as well as help prevent future issues as some of these devices are prone to fail in oroginal locations.

 

Excellent write up... Thanks for the great contribution! Your persistence payed off in the end. Diagnosing an issue is a lost art that 50% (maybe more) of "mechanics" don't possess. You on the other hand should pat yourself on the back! Well done:clap:

 

Yes, this is awesome!!! Any mods who sees this may be can be part of sticky???

 

deejaa,

Incase you missed in my post just three threads above yours, here is a little refresher for you

I appologize if you assume I am cursing you or other individuals, this is not my intent and sometimes words can be misinterpreted through the internet

 

Good job man,glad you got her fixed.
shows again that more or less the same symptoms can be caused by diff parts going wacko

Good writeup too.

 

So when your truck was acting up, there was no service throttle soon light, and no check engine light?

 

I had reset all codes on the truck as prior to my purchasing, the SES light was not working. It was a simple bulb replacement and 7 codes were stored not including the DTC-25 or DTC-35 at that point.

After driving the truck several runs, this is a project, the SES light did come on but not the Service Throttle Soon Lamp. The SES light did not stay lit, just popped on for about 5 seconds and went off.

Came back to retrieve codes and had the DTC-25.

 

in some further research with a buddy of mine, we have found that the reference voltages I was getting seem quite common, the fact that the problem goes away with the new pedal suggests that there is a problem with the internal variable resistor in the pedal assembly which would also explain the hesitating and bucking.

The other issue with the fact that it acted like an injector pump could also be caused by the same issue with the pedal as it uses this to control the pump as well. I am going to modify the savana pedal to fit directly in place of the old unit and then drive it as is as this seems to have solved the problems.

furthermore, the truck does not shut off whenever it feels like it and continuously stays running which suggests that the injector pump is ok.

The engine does idle at approx. 700 in park/nuetral and this will vary when driving from 500 to as much as 1000 rpm when coasting until I trigger the brake sensor on the pedal, at which time the engine goes to its normal idle speed. this is due to the fact that the engine is used as a partial braking device when coasting with no pressure on the accelerator pedal.

 

So if you had to buy one how much is an APP and how do you replace it?

 

Can anyone explain what the APP is?

 

from the top of the page.. 6.5 faq.. NEW MEMBERS READ

APP (Accelerator Position Potentiometer) - This acts as a throttle cable through the drive-by-wire system. Commonly known as an APPS (Accelerator Pedal Position Sensor).

I will pass this on to a mod to sticky

 

Don't know about making it a sticky (Don't wanna clutter up the opt of the page too much)..... But I added a link to it in the FAQ at the top of the page under "APP - How to tell when it's bad" :thumb:

 

thanks joe, i had sent the link to Green to do exactly that. with you around, theres nothing for any of us to do lol

 

Well, I'm not around ALL the time : ):h

 

What is APP? Acceleration pedal?

 

APP (Accelerator Position Potentiometer) - This acts as a throttle cable through the drive-by-wire system. Commonly known as an APPS (Accelerator Pedal Position Sensor). Failure modes for the APP system are as follows:
If only one sensor fails, the vehicle will operate normally. The PCM will store a DTC, but will not illuminate the “Service Throttle Soon” lamp in the instrument cluster.
If two sensors fail, the engine will operate at reduced power. The PCM will store a DTC and will illuminate the “Service Throttle Soon” lamp.
If all three sensors fail, the PCM will store a DTC and illuminate the “Service Throttle Soon” lamp. The PCM will also reduce engine power to idle.
How to tell when it's bad. http://www.dieselplace.com/forum/63...um/63-gm-diesel-engines/21-6-5l-diesel-engine/369589-injection-pump-my-azz.html