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New and random stalling issue

revyd

revyd

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New to this forum and relatively new to the 6.5 although I've had a GMT400 for at least 20years.
My truck is a 1995 Silverado K3500 dually. A previous owner made some mods that have been disastrous. He put electric fans on the tranny and oil cooler then took off the fan clutch and replaced it with a flex fan, and needless to say had some serious heat issues. I got rid of the electric fans, changed out the water pump to a newer version, put in a hayden severe duty fan clutch and a duramax fan. Overheating issues gone. However the damage was done so now I have a new used motor. I replaced the oil cooler lines with some custom lines and added an HO cooler from a 98. I relocated the oil filter and added a new 2.5" crossover pipe. Since then it's been pretty reliable except for one thing.
On very random occasions right after I start it, usually just after I put it in gear and start moving, it stalls. It doesn't seem to matter if it's hot or cold and it has never done it to me while I"ve been driving. I've gone through all the grounds, I put in a new lift pump but it's still happening. I don't get a check engine light but I have to crank it quite a bit to get it to start after it stalls. My suspicion is fuel but I don't know where to start.
 
Welcome to the forum @revyd.

start out with some basic diagnostics before firing the parts cannon too much.

remove the 1/4" hose from the IP return line and replace it with a clear hose from the hardware store. the hose is about 6" in length and shaped like an upside down U from the top front of the IP to a small steel line behind the timing cover. this will allow you to physically see if there is any air intrusion in the fuel system. Don't worry about the clear hose being fuel resistant, there is no pressure on this hose and several of us run this hardware store hose for several years before needing to replace it.

next get a fuel pressure reading after the fuel filter, best to test at the IP inlet. Harbor Freight sells a fuel pressure test kit that includes a tee that you can temporarily plumb into the hose at the IP. the gauge should reach out to the windshield so you can pin it under the wiper blade and watch as you drive. you should see 8-10 psi with key on and maintain 6-8 running. it will dip lower under load but should never go into a vacuum. Starving the IP for fuel will kill it in a hurry.

When it stalls, does it stumble or any smoke come from the tail pipe? or does it feel like something luggs the engine down and kills it? if not fuel issue the other thing that comes to mine is if your TCC is locking up and killing the engine. this would be a wiring issue.

Start with the clear hose looking for air and check fuel pressure and report back. there are lots of us here that can help wrench on your truck and help spend you money LOL

if you can post videos linked through youtube or even photos it might help too.
 
dbrannon79 said:
Welcome to the forum @revyd.

start out with some basic diagnostics before firing the parts cannon too much.

remove the 1/4" hose from the IP return line and replace it with a clear hose from the hardware store. the hose is about 6" in length and shaped like an upside down U from the top front of the IP to a small steel line behind the timing cover. this will allow you to physically see if there is any air intrusion in the fuel system. Don't worry about the clear hose being fuel resistant, there is no pressure on this hose and several of us run this hardware store hose for several years before needing to replace it.

next get a fuel pressure reading after the fuel filter, best to test at the IP inlet. Harbor Freight sells a fuel pressure test kit that includes a tee that you can temporarily plumb into the hose at the IP. the gauge should reach out to the windshield so you can pin it under the wiper blade and watch as you drive. you should see 8-10 psi with key on and maintain 6-8 running. it will dip lower under load but should never go into a vacuum. Starving the IP for fuel will kill it in a hurry.

When it stalls, does it stumble or any smoke come from the tail pipe? or does it feel like something luggs the engine down and kills it? if not fuel issue the other thing that comes to mine is if your TCC is locking up and killing the engine. this would be a wiring issue.

Start with the clear hose looking for air and check fuel pressure and report back. there are lots of us here that can help wrench on your truck and help spend you money LOL

if you can post videos linked through youtube or even photos it might help too.
Click to expand...
Thanks for the response.
I can answer a few questions, but I'll get onto the clear hose and fuel pressure kit later.
It does not stumble, it just stops. No smoke from the tail pipe. It does not feel like any drag on the engine.
The transmission was rebuilt about a month ago, but I can't rule out the wiring issue since it was doing it prior to the rebuild.

The fact that I have to crank for a bit before it starts again leads me to think it's fuel over wiring. Or fuel starvation anyway.
 
if it's fuel starvation, both the clear hose and reading pressure will reveal it. do you have anything to read the PCM for codes? you can do the paper clip and count the flashes but for these trucks with the diesel, there are really only two trusted scanners that can read codes and live data along with checking and setting timing. GMTDscan for the laptop or a GM Tech 2
 
dbrannon79 said:
if it's fuel starvation, both the clear hose and reading pressure will reveal it. do you have anything to read the PCM for codes? you can do the paper clip and count the flashes but for these trucks with the diesel, there are really only two trusted scanners that can read codes and live data along with checking and setting timing. GMTDscan for the laptop or a GM Tech 2
Click to expand...
My wife is going to love that I'm buying more tools. :)
I have a reader that replicates the paper clip, and I count flashes. I have never heard of the GMTDScan, but it looks like a brilliant option.
 
Here is the official website. it's from Sweden. you can build your own cable to connect to the truck's connector with a device from the jungle site like I did vs paying the extra $50 for a pre-made cable. the free version of the software will read and clear code and read live data, but to do any of the functional tests or set timing you have to get the paid version which is about $100 usd. The drawback is it only works on the 94-95 GM 6.5 diesel trucks. investing into a GM tech 2 will get you a lot more versatility across multiple vehicles made from GM.

keep in mind that since you replaced your engine, you will need to set the timing, the only way to set the TDC offset is by using one of these scanners. side note: Snap-on scanners will do it but are known to give false timing data.

you can even get a CKO tech 2 from ebay (Chinese copy) Just don't try updating it or it will brick.

anyway here is the link to GMTDscan and another link to make your own cable along with the device I used from amazon to make my cable. plus the chinese tech 2. just depends on your budget and if you have or want to use it on other vehicles in the future.

GMTDScan – The #1 scan tool for 1994-1995 GM 6.5TD trucks.

www.gmtdscan.com www.gmtdscan.com

www.dieselplace.com

How To: Scan your OBD1 6.5 for less than $10!

www.dieselplace.com www.dieselplace.com


and the alternative CKO GM tech 2...
www.ebay.com

Tech2 II scanner + candi module GM/SAAB/OPEL/SUZUKI/ISUZU/HOLDEN Free Shipping | eBay

TECH2 Scanner Support 6 Softwares (forGM,OPEL,SAAB ISUZU,SUZUKI,HOLDEN) diagnostic tool. candi interface. SAAB-English Card 148.000 version covers Saab 1998 thru 2012. GM-English Card 33.004 version covers GM vehicles 1991 thru 2013.
www.ebay.com
 
As an Amazon Associate we earn from qualifying purchases.
You could also try moving any part of the harnesses under the hood or around the PCM while it's running. I think you mentioned grounds were checked, if not there should be three grounds that connect to the rear of the intake near the trans dipstick tube, and one on the IP that ties into the harness under the intake. make sure body to frame grounds are also good.

you mentioned it dies without cause when trying to move the truck under it's own power. its possible the frame to block ground might have an issue. Also look up on the upper section of the trans bell housing where it meets the block. any pinched wires there if/when the trans or engine was installed can getcha too! I've seen that happen before.

one way to check ground paths is to use a ohm meter with one probe at the ground wire on the PCM and the other on various places on the engine block and frame looking for resistance readings. also doing the same with the ground wire in the harness of the PMD and making sure the PMD it's self is also grounded where it's mounted. but do this with the engine off.

I know you will hear us preach a lot about grounds, but one single bad ground can reek havoc for anyone!
 
Thanks everyone for the ideas.
I'll check all the grounds again the next chance I get. If anyone has any suggestions, I may also consider doing a battery cable upgrade.
Then, I’ll pick up a fuel pressure testing kit and see if there are fuel issues. Then, if nothing else helps, I’ll look at the PMD and finally the ignition switch.
 
revyd said:
Thanks everyone for the ideas.
I'll check all the grounds again the next chance I get. If anyone has any suggestions, I may also consider doing a battery cable upgrade.
Then, I’ll pick up a fuel pressure testing kit and see if there are fuel issues. Then, if nothing else helps, I’ll look at the PMD and finally the ignition switch.
Click to expand...
You might be just as well to get set to install a permanent fuel pressure gauge.

You can always temporary it for now.
 
Just if you go the permanent route. use electric or get a gauge isolatior. others can attest to this but you do not want a live fuel line running into the cab!!

if you don't have anything mounted there already, a nice place to mount a gauge such as this, (something you don't watch all the time while driving) is up on the center console above the rear view mirror.

Here is a photo of my boost gauge mounted there. all I did was take an old piece of scrap wood from a pallet and wittle it down to fit, used the same screws that held the plastic insert to hold it. there is room here for two gauges. my vote is a fuel pressure gauge and an EGT gauge (exhaust gas temp) the probe for this goes in the drinkers side manifold under the turbo. there are several writeups on this.

at some point I would like to get one of those offset rings so that the gauge is more angled towards me but its functional as it.

on the fuel pressure gauge. if you go with an isolator, you can get a boost gauge that shows -15-0-15 psi gauge. this will show when the fuel system goes into a vacuum when there is a real issue like the LP failing. most fuel pressure gauges only show positive pressure and it's even harder to get one that maxes out at 15psi.

1728694058965.png
 
dbrannon79 said:
Just if you go the permanent route. use electric or get a gauge isolatior. others can attest to this but you do not want a live fuel line running into the cab!!

if you don't have anything mounted there already, a nice place to mount a gauge such as this, (something you don't watch all the time while driving) is up on the center console above the rear view mirror.

Here is a photo of my boost gauge mounted there. all I did was take an old piece of scrap wood from a pallet and wittle it down to fit, used the same screws that held the plastic insert to hold it. there is room here for two gauges. my vote is a fuel pressure gauge and an EGT gauge (exhaust gas temp) the probe for this goes in the drinkers side manifold under the turbo. there are several writeups on this.

at some point I would like to get one of those offset rings so that the gauge is more angled towards me but its functional as it.

on the fuel pressure gauge. if you go with an isolator, you can get a boost gauge that shows -15-0-15 psi gauge. this will show when the fuel system goes into a vacuum when there is a real issue like the LP failing. most fuel pressure gauges only show positive pressure and it's even harder to get one that maxes out at 15psi.

View attachment 90119
Click to expand...
I really wish a vendor would sell fuel gauge kit. One vendor told me that everything was available, nomoney in a kit.
The same is true of the engine oil cooler kits, but a lot of people buy those.
 
It’s like the fitting for the ds4 to supply the location for the pressure sensor:
ModMafia sells it but most people won’t buy from him because they can save $15.
Unless there was something specific to it, people will just look at it then go shop amazon
 
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