ecm electrical nightmare

soooooo... im having a problem with my 6.5 not starting. fim is fine, probably the fuel injection pump, but im trying to do some real diagnosis to see what's going on with my truck and cant even comunicate with the ecm. i can comunicate with the abs module, but that's it. i did some pin outs to the pcm and checked continuity to the pcm for the dlc connector and there is continuity to each part, and the ecm, not even .01 resistance. then checked the 2 grounds in the ecm's connector and there's 3ohms of resistance in both.

tried using another ecm from another truck of the same year, but 4x4 and the truck was just freaking out. dont know if it was simply because the batteries were dead, or it really isnt compatible with my vehicle(4x2), but it still wouldn't communicate with the ecm(scan tool-snap on), and would only communicate with the abs module.

im trying to get some advice from someone that knows the direction of testing, or physically looking at this thing. i've no problem chasing every wire if i have to but i'd rather not do that blindly. same with diagnosing my truck. i really want to be able to see what's happening in my truck on a scan tool. i have an idea that i need to chase down why i have the 3ohms of resistance in the grounds, as the ecm for signal references uses only 5v reference signals, and wouldn't hardly be able to provide any signal what so ever. but im unsure, and would like someone's imput on this.

p.s. it's a 97 2500

Hi

What scan tool are you using ???

Most off the shelf tools will not talk to the 6.5 system...

What brought you to this point ??? (Engine stopped or???)

SES light on ???

Codes ????

With minimal exceptions the PMD is always suspect on a no start.

Has the PMD been mounted on a remote cooler ???

GOOD BATTERIES ALL TOPPED UP.
Air free fuel to the IP (lift pump works)
Glow plug system, working (plugs confirmed to heat)
Starter spins the engine well (spec is 200 rpm)

Failed PMD will usually not set a code.

I have a 97 ECM from a 2WD Auto truck if it turns out to be your ECM
Let me know and i will get it in the mail ASAP

the scan tools i've been using are snap on scan tools, verus, zeus, and another one i cant remember.

what brought me to this point is that my truck was randomly shutting off as i was driving and turning into the nutless wonder. now it wont run at all. before you say fuel injection module, i've used it on another 6.5 and it ran. that's not the problem. at this point i know it's the fuel injection pump that is bad because we sprayed some silicone spray in the intake and it lit right up. also i have it placed on the bumper underside, screwed to an aluminum heat sink with silicone paste.

what i need help with figuring out is why my ecm wont communicate with a scan tool. the ecm is still running the vehicle. it just wont communicate with a scan tool. as stated in the origional post, there is continuity between all data lines and the pcm, it's just not doing anything to communicate. also an update on those grounds for the ecm having 3ohms of resistance is no longer a thing. i found their terminating point, and replaced it where it should be. now instead of 3+ohms, there's less than .02ohms. anyway, that obviously didnt solve my problem with the ecm not communicating, though im sure that it will help in the long run.

as for codes. lol i cant communicate with the ecm, so i'd love to tell ya but if i could read codes, i'd probably not be on this page hoping someone had an idea of what my problem is and what i have to do to amend it.

yes fuel is getting where it needs to be, all the way up to the pump. turn the key to on and bleed the fuel filter and it just skeets everywhere.

starter is brand new, and batteries are crap but they are good enough to operate with a chager, and lastly the glow plug system is fine. clam relay is working properly and control is cycling like it should be. and yes ses light is on.

so to really clarify as to what kind of direction im looking for here. i need help trying to figure out what wires i need to be looking at, and testing, to figure out why i can (provided my fuel injection pump worked) run the truck off my ecm, but cannot communicate with it.

if necessary i can provide some pics of diagrams at some point. but it will be a while before i can. lol gotta remember to get them and upload them to do that.

Hmmmmm

Have you checked the fuel shutoff relay ???? (Round cylinder shaped part on top of the IP near the front)

Get a helper to turn the key on and off (not cranking) and the relay should CLICK loud enough to be heard and felt if you touch it.

Be sure you have good voltage to the power box (fuse box under the hood)

Low voltage will drive these things nuts.

The alternator feeds the left hand battery and the starter is fed off the right battery.

A bad ground on the RH battery or bad positive connection at the RH battery can still allow the starter to function, but leave the needed power to the main feed lacking.


The only scan tool that will reliably interface the 6.5 is the TECH 2 USED BY GM

GMTD SCAN MADE A DOWNLOADABLE package for a laptop but these are for 94 AND 95 OBD 1

Quote:

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Originally Posted by curbrider

what i need help with figuring out is why my ecm wont communicate with a scan tool. the ecm is still running the vehicle. it just wont communicate with a scan tool.

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As Robyn said, your scan tool won't communicate with the 6.5L ECM due to the fact that your scan tool does not come loaded with the proper 6.5L diesel software. The genuine GM Tech II is the only scan tool I know that works properly.

Casey

for the love of god and all that is holy. ty so very much. genuinely. that sucks, but at least now i have a direction to go in. i need to communicate with this thing, and not being able to is frustrating.

quick question though, are snap on scan tools capable of downloading supposed software and using it to communicate with the 6.5? if so, it would be great. but yeah. still no idea about that. i mean if it's online and can be downloaded, snap on scan tools can use internet browsers and could probably download the software directly.

side note, i've apparently been using a snap on scan tool that's been used on several 6.5's and it's never had a problem communicating with any of them.

Interesting...

If you can get access to another 6.5 truck ...plug that scan tool in and see what it says...

If the scan tool will talk to a different truck then the issue may be the ECM in your truck has issues...

You need to get some data here to guide you.

If that tool has worked on other OBD2 6.5 trucks, then it should work on yours.


See what you can scare up.

GOOD LUCK

Quote:

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Originally Posted by curbrider

quick question though, are snap on scan tools capable of downloading supposed software and using it to communicate with the 6.5?

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Everything I have read states that some Snap-On scanners can communicate with the 6.5L, but when they do, they don't offer accurate information; in other words, if you can get the tool to "talk" to the ECM, you can't get the right information you need anyway.

GM Tech I or Tech II is what you need. However, the majority of folks discover that you can troubleshoot just fine without it. The only time a Tech I or II is absolutely needed is to set the TDC offset when replacing the injection pump. Most of the 6.5L no start or stalling issues are related to the PMD/FSD.

Casey

yeah, that's basically the direction im looking at, at this point. tried getting a used ecm, but that didnt work. may need to get it programmed specifically for my truck. only difference to it was that it was 4x4 though. anyway, guess im waiting till i find a good one and a way to program it.

Quote:

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Originally Posted by curbrider

yeah, that's basically the direction im looking at, at this point. tried getting a used ecm, but that didnt work. may need to get it programmed specifically for my truck. only difference to it was that it was 4x4 though. anyway, guess im waiting till i find a good one and a way to program it.

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Hi Curbrider
I have a ECM from a 97 Auto 6.5 2WD Truck was working fine when i pulled the engine,truck had a bad tranny.
Let me know if you are interested.
Thomas