6.5 stalling / hard start

[treegump]

something that caught my eye reading this was that you guys said the LP continues to run for about 10-15 seconds after you turn the key off. I've never noticed that (but I'll be sure to listen next time I turn the key off). If its not running, would that mean the OPS is bad? My truck seems to be running as usual - but hiccupped saturday night. I changed the fuel filter, and pulled the ratty K&N filter out and put a clean STP air filter in. I'm blowing smoke easy, but after changing those things I noticed it "hiccupped" twice more yesterday and 1 or 2 times this morning on my 32 mile commute. When my tank gets low - I'll try and drop it and check the sock - since I haven't done that since I bought it. Also, I noticed a "Last ditch screen" on http://www.thetruckstop.us/forum/showthread.php?t=6872 . Is that included with the fuel filter, because I've never seen it before. I've also yet to check the fuel pressure - I have the gauge, and I have T's, and the hose, just unsure where I plug it in. Do I cut the fuel line between the filter and bleeder T and stick another T in there to route the pressure hose?

 

[JMJNet]

something that caught my eye reading this was that you guys said the LP continues to run for about 10-15 seconds after you turn the key off. I've never noticed that (but I'll be sure to listen next time I turn the key off). If its not running, would that mean the OPS is bad? My truck seems to be running as usual - but hiccupped saturday night. I changed the fuel filter, and pulled the ratty K&N filter out and put a clean STP air filter in. I'm blowing smoke easy, but after changing those things I noticed it "hiccupped" twice more yesterday and 1 or 2 times this morning on my 32 mile commute. When my tank gets low - I'll try and drop it and check the sock - since I haven't done that since I bought it. Also, I noticed a "Last ditch screen" on http://www.thetruckstop.us/forum/showthread.php?t=6872 . Is that included with the fuel filter, because I've never seen it before. I've also yet to check the fuel pressure - I have the gauge, and I have T's, and the hose, just unsure where I plug it in. Do I cut the fuel line between the filter and bleeder T and stick another T in there to route the pressure hose?

Not necessarily, you have to do the LP/OPS test. First t-valve, if there is no fuel then the 12V direct source to the LP. If the LP runs, then OPS is bad.

My suggestion is to create a new thread so you get more attention.

 

[treegump]

Not necessarily, you have to do the LP/OPS test. First t-valve, if there is no fuel then the 12V direct source to the LP. If the LP runs, then OPS is bad.

My suggestion is to create a new thread so you get more attention.

thanks - i'll run the tests you've mentioned, and start a new thread if that doesn't turn up anything.

Thanks again!

 

[Missy Good Wench]

The later trucks (OBD2) power the lift pump from the ECM through the relay and not with the OPS.

95 was the last year for the OPS circuit to directly power the LP

The 94 will see the LP run on after a cold shut down until the pressure falls off to neat zero.

The 95 is wired differently but still uses the OPS in the circuit

A 95 system will allow you to place the gear selector in D and then turn the Key to start and the LP will run and prime/fill the fuel filter.

The 94 will not, must be done from under the hood by connecting the fuse in the junction box to 12 V stud (The fuse has a little bare slot in the face and touching it to the 12V stud will power the pump.)

Grounds, +++ connections, batteries, alternators are all very fussy on these trucks and if issues exist can drive you nuts.


Poor running that just comes on Poof, many times can be traced to poor connections, ground issues and of course bad batteries.

The main ++++ Bus bar (stud) in the junction box should see 14V to 14.5 with the engine running at idle.

Low voltage down in the 12.5 area or below will/can definately cause all sorts of grief.

The areas in the red +++ side terminal jeckets are a prime spot for corrosion where you can't see it or get to it.
The ground cables, Same thing. The ends of the grounds that connect to the block are also to be suspect.

The cables are crimped and surface soldered (some older factory cables) and the core can corrode to the point that the connection is poor to non existant.

Aftermarket cables (parts store stuff) can be absolute junk and fail within a couple years.

The best solution is to use fully soldered copper EYE's on 00 welding cable (Fine wire) and fasten these using top terminal batteries and cable ends depending on the battery.

I use optimas which have both top and side terminals.

The 94 charges the LH battery and the power to the truck is fed from ther RH battery.
The 95 charges the LH battery and feeds the power from the LH one too. The starter is fed off the RH battery.

The 96 and later have the alternator on the RH side and I am not sure where the alternator feed is but these things are all areas to be checked from time to time.

Another area that ccan snag you is the batteries. If the battery thats feeding power to the chassis is the bad one (shorted cell or ??) there will be a limited availability of voltage getting to the ECM and other stuff that requires major power.

Just a matter of making usre that all is well with the power delivery.


Now GM does not have the best volt meters in the business so I dont really trust them much.

Checking with a known good VOM is the best practice and doing the check at each battery to make sure that the difference between the two is not more than a couple tenths of a volt and that the supply to the chassis is 14V minimum with the engine running.



Missy

 

[treegump]

Thanks Missy - I have yet to go over all my grounds as well. With a new house/yard/g/f, I'm trying my best to get to everything that needs to be done. I'll put the grounds on my priority list after an easy check of the T valve. Just to clarify though, I can't do the 12V test with my 96?