96' Jimmy-Haunted? Fuel Delivery Problem!

[old_master]

The dealer, of all people, should know that to diagnose an intermittent problem, you need to have the test equipment connected when the problem is happening. All the testing and checking in the world won't find a problem that's not there.

[azeporo]

so what did you finally find out? iM having same problem with my 96 astro!

[JimmyRiggin']

its been there for 3 days now and they can't get it to malfunction, like Om said they can't find a problem if it isn't happening. The guy said instead of racking up some more shop hours, I should just pick it up, so I am going to right now. I have been reading the article OM wrote regarding fuel pressure on my cmfi, I have a few idea's I'll post back.

[jaysun029]

Originally Posted by JimmyRiggin'

its been there for 3 days now and they can't get it to malfunction, like Om said they can't find a problem if it isn't happening. The guy said instead of racking up some more shop hours, I should just pick it up, so I am going to right now. I have been reading the article OM wrote regarding fuel pressure on my cmfi, I have a few idea's I'll post back.

Dude, your problem sounds almost EXACTLY like mine. I was driving down the interstate....bam! engine cuts off at 70mph! I pulled off, looked under the hood. No leaks, smells or damage that I could see. It sat for 15 min and started up, running rough. I got 1/4 down the road and it stalled again! I looked under the car and see fluid near the transmission. But it looks like it's coming from about the tranny somewhere.

Temp was normal and everything so I know it didn't overheat. Fuel pump maybe? The fluid didn't have a gas smell. I'm at a loss here.

Jay

[JimmyRiggin']

Well I thought I had it solved again, fuel pressure was holding strong at dealership. I figured out how to make it die now... it has to be heated up and driven, then shut off and quickly started (about 2-3 mins off) just enough time for the heat to build up. It will still only malfuntion on a hot day. I changed the deteriorating fusible link/pos battery cable out, she drove fine for a couple weeks, then as soon as I started punsihing it on a hot day, it quit.

It is obvious to me now that it is a hot thing, What could possibly be overheating on the top end of my engine and causing my fuel pressure to drop into the 30's, and make the fuel pump to start sounding different?

[old_master]

It could be the fuel pressure regulator, any one of the lines in the plenum, or the check valve in the fuel pump. The pump needs to be isolated from the system when the problem occurs, the results will determine if the problem is the fuel pump or in the plenum.

[JimmyRiggin']

Old Master, I was reading your article on fuel pressure and I was about to get started when I noticed something.

My fuel system is "CSEFI" which doesn't seem to appear in your article. I checked my VIN, the 8th character is a W. So would the info still apply even though it is not CMFI or CSFI? Or maybe CSEFI and CSFI are one and the same?

Thanks again.!

[old_master]

CSFI, (Central Sequential Fuel Injection) and CSEFI, (Central Sequential Electronic Fuel Injection) are the same thing, just a fancier name.

[JimmyRiggin']

Hey, apologies for the extremely late update.... and resurrecting this thread but I have recently returned to this forum and wanted to close this thread out properly.

Anyway, I ended up replacing the fuel sending unit (again) at the GMC dealership... around 20 months ago, along with a ton of other upgrades I added myself which I don't really want to list in this thread. Pics and info are coming in the appropriate thread.

Long story short, I did the repair at a quality, (and equally expensive) repair shop and it seemed to make a huge difference. I have put roughly 50000KM on the Shimmy since the repair(s), and the problem has not returned. It will now start and run fine in even the worst of conditions.

I now realize how important and critical proper fuel pressure is with these engines, and how an unqualified or overconfident mechanic could easily do an improper repair, resulting in fuel delivery failure at any given time, for any number of reasons.

Mods*/Admin* feel free to close off this thread if you wish. Thanks for all the help guys!

[djd99]

Originally Posted by JimmyRiggin'

Hey, apologies for the extremely late update.... and resurrecting this thread but I have recently returned to this forum and wanted to close this thread out properly.

Anyway, I ended up replacing the fuel sending unit (again) at the GMC dealership... around 20 months ago, along with a ton of other upgrades I added myself which I don't really want to list in this thread. Pics and info are coming in the appropriate thread.

Long story short, I did the repair at a quality, (and equally expensive) repair shop and it seemed to make a huge difference. I have put roughly 50000KM on the Shimmy since the repair(s), and the problem has not returned. It will now start and run fine in even the worst of conditions.

I now realize how important and critical proper fuel pressure is with these engines, and how an unqualified or overconfident mechanic could easily do an improper repair, resulting in fuel delivery failure at any given time, for any number of reasons.

Mods*/Admin* feel free to close off this thread if you wish. Thanks for all the help guys!

This is exactly why if you suspect your fuel pump you should purchase a fuel gauge and tape it to your windshield, then when your truck dies you know exactly what your pump is doing when it dies. In this case most likely it loses pressure.