Ghost in the Machine...

[454cid]

Some trucks have a pressure sensor on the fuel pump, that looks a lot like a MAP sensor. If your truck doesn't use that sensor, maybe you have the wrong pump. I wouldn't think that would be the source of the problem, Though. When buying a fuel pump you have to get one with the right code. It's not an RPO code, like what would be found on SPID sticker, but I can't think of the name right now.

Fuel pumps are harder to pick out than other autoparts, it's more than just make, model, and year, and engine. Mine uses a GFT pump. The first time I replaced mine, I just went to the dealer, and bought it.... they gave me a decent price too. When I had to replace that pump, I took a picture of the code, so I'll have it when I forget.

 

[RichLo]

Still haven't done anything with the EVAP system???

 

[AK49BWL]

No mention of the canister vent solenoid? The purge solenoid isn't the only one on 98+ trucks... Although the tank pressure sensor being disconnected is a pretty big red flag, as the 98+ trucks are supposed to be using it as well. Probably why the vacuum is so strong, the pcm never sees a change so never changes its routine. Surely you have an SES code or two?

 

[454cid]

No mention of the canister vent solenoid? The purge solenoid isn't the only one on 98+ trucks... Although the tank pressure sensor being disconnected is a pretty big red flag, as the 98+ trucks are supposed to be using it as well. Probably why the vacuum is so strong, the pcm never sees a change so never changes its routine. Surely you have an SES code or two?

He has a 1-ton, like I do..... there probably isn't a solenoid on the canister. I assume it's the GVW that allows GM to leave that off.

 

[someotherguy]

I can vouch for the tank pressure sensor not being used on the 3500's as well. No harness there for it, just for the pump/sender connection. This pic is from a 1999 (classic) C3500 5.7/4L80E RCLB parts truck I had. My 1998 C3500 7.4/4L80E CCLB was the same setup. Actually I think I have that backwards, the pic is from the 1998.. either way same tho.

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Richard

 

[AK49BWL]

Oh. I stand corrected lol.

 

[stutaeng]

Doesn't EVAP require a tank pressure sensor? How is the ECU supposed to know when to vent to atmosphere or open purge solenoid for gas vapors from tank to be sent to intake for combustion? Or are you saying the 3500s didn't have an EVAP altogether?

Purge solenoid is supposed to be normally closed and only opened as commanded by ECU. I bought one for my 06' Suburban because it had an EVAP small leak code and new one from auto parts store didn't hold vacuum, so I had to return it. Unfortunately, that wasn't the problem in my case.

The GMT-400s had the charcoal canister (and vent solenoid?) under the hood, and the components hardly ever failed. When they moved them to under the trucks in the newer generations they seem to fail more often. Ditto for the ABS control module.

 

[454cid]

All modern vehicles have an Evap system. The 1-tons have a valve/solenoid/something on the intake manifold, but nothing but a vented cap on the charcoal canister.... although, I think there is a solenoid listed for my canister, it's kind of like the heater core shutoff.... there's one listed, but it was never on my truck from the factory.

The move of these component to under the frame was a terrible idea...... I had a van at a previous job that needed multiple trips for repair, and eventuall $$$ to fix. The stupid thing would act like the tank was full while running on empty. This happened in the winter of course, so it took forever to get gas in it.

 

[alpinecrick]

Does it fill slowly? I had a problem with new filler neck on my ZR2.

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What the snarf is that? Did somebody stick a marshmallow in your filler?

 

[someotherguy]

Doesn't EVAP require a tank pressure sensor? How is the ECU supposed to know when to vent to atmosphere or open purge solenoid for gas vapors from tank to be sent to intake for combustion? Or are you saying the 3500s didn't have an EVAP altogether?

Purge solenoid is supposed to be normally closed and only opened as commanded by ECU. I bought one for my 06' Suburban because it had an EVAP small leak code and new one from auto parts store didn't hold vacuum, so I had to return it. Unfortunately, that wasn't the problem in my case.

The GMT-400s had the charcoal canister (and vent solenoid?) under the hood, and the components hardly ever failed. When they moved them to under the trucks in the newer generations they seem to fail more often. Ditto for the ABS control module.

From the mid-90's and older, there were no tank pressure sensors on GMT400's of any GVWR spec. They all have EVAP systems though. 94 was first year for solenoid control of the purge valve. How those systems operate year vs. year, beats me; never needed to look into it.

Richard