engine cuts out on long trips

[irish]

So get a load of this:
After driving about 70 miles on the highway, my truck starts bucking and jumping like someone's under the truck turning the fuel pump on and off. It never happens until I drive a fair distance at a relatively high speed. Sometimes if i turn it off, prime the fuel pump a few times it completely dissapears--other times I've had to have it towed.

I've recently replaced the cap, rotor, plugs and wires. Air filer's clean, PCV valve appears to be fine, no loose wires or bad connections that I can find (although I will be investigating this more). Even stranger is that it never throws a code of any kind (and yes my SES light works). Although if the bucking goes on long enough sometimes the SES will flash rapidly.

I've got to drive to NC in a couple weeks and I can't afford to break down on the way. Any one seen this before?

[irish]

Wow this is not the right section... I meant to put this in the 4.3L section. Can I get a mod to move this please?

[lesterl]

Doesnt look like mod has moved ya, try testing the fuel pressure first.

http://www.harborfreight.com/cpi/cta...emnumber=92699

Guage for $13, if you have a Harbour Freight store close by you can run and pick it up, if not maybe purchase online?

P.S. you forgot year of your S10 if TBI then the guage wont work.

[irish]

it's a 2001 so i guess its spfi. i'll have to give that gauge a shot though. the problem i'm having with diagnosing the problem it's pretty much random.

i guess i should also mention that i had to take the fuel sending unit out a while ago to deal with some issues i was having with the evap system. i was a little confused when i put it back in--it looks like the inlet port of the pump housing just smashes against the bottom of the tank.

do you know who i can pm to get this moved btw?

[irish]

Picked up the gauge at harbor freight today for $10--awesome. Fuel pressure looks normal according to the haynes manual:

Haynes
Key on 55-61 PSI
Idle 45-58 PSI

Me
Key on 57 PSI
Idle 50 PSI

I'd like to test this while driving under highway conditions but obviously that may prove to be more difficult than its worth.

[lesterl]

I have no idea on the MOD's, the pressure on a 2001 should be right around 60 PSI, IDK why haynes is quoting so low, people always show #'s like that when having issues with fuel pump. Might duct tape the guage to the windshield if possible?

How many miles, I just about bet you have a flakey Fuel Pump.

2001 would be a CSFI, there is a MPFI upgrade available for these that runs around $300, but there is no performance difference unless your Spider is messed up to begin with. 2003 and newer have the MPFI spider. The difference between the two systems is the location of the injectors. The CSFI has the spiders in the fuel regulation box and poppet valves at the ends of the spider legs. The MPFI has the injectors at the end of the spider legs.

[irish]

Haynes shows 58-64 PSI key-on pressure for CMFI and 55-61 PSI for CSFI but I'd certainly trust real-life measurements over what's in this book. I noticed under 100% load my fuel pressure kicks up to about 60-62 PSI--of course the manual doesn't mention anything about that.

The truck as 70k miles on it. Manual transmission locked up on me while I was doing about 70 MPH on the highway--apparently the input shaft bearing decided it'd had enough. Also had a problem with the evap purge line not making a good seal with the fitting on the EVAP can--sucked up enough dirt to ruin that. Other than that I've not had a problem with the truck.

[lesterl]

Hmmm, would have to have the thing acting up to check a few things, like when dead will it fire up off a shot of carb cleaner/ starting fluid? Does it have spark then? Etc.

[irish]

Well I just drove over 1300 miles to Banner Elk, NC and back with no problems. It's still hiccuping every now and then under heavy load but fine otherwise. I didn't try hitting it with starting fluid, it never has any trouble starting or idling.

[irish]

Ok, now I just drove 100 miles to the beach and back and almost didn't make it home. According to my OBD monitoring tool, my fuel trim is going through the roof during the times when the engine is cutting out so I assume this means the fuel is being delivered. I've also noticed this problem only occurs during hot weather...

[lesterl]

O2 sensors, CTS, IAT sensor. Check those for loose connections/ corrosion, replace if nescessary.

[irish]

Just an update: checked critical connections, seals, wires, etc.--no obvious problems but I'm still looking. The $#!& is really hitting the fan now though and I was able to observe the problem in detail. Today was unusually warm and it was sputtering, kicking, and stalling all over the place. There's a video of the fuel pressure gauge and tachometer in the link below along with sensor data from the problem--engine speed never climbs above 1500 RPM or so at wide open throttle, just lots of backfiring and strange smells.

The ODB system still reports running extremely rich during this time, the fuel system switches to closed loop mode but nothing changes. I've replaced all of the ignition components except the distributor and coil. The fuel pressure never seems to change when the problem occurs, however, after stalling, the fuel pump becomes unresponsive and the truck won't start. After waiting about 30 sec the pump comes back to life, fuel pressure returns to normal and the truck resumes running rough.

What's even stranger is I'll go out there tomorrow morning and drive it to class with no problem until it gets nice and hot outside...

Video, ODBII sensor data:
http://rww.causeymachine.com/010/

(you may have to right-click, save as on these files)

[lesterl]

I would put a liteup switch on the fuel pump so you could kick it in when it acts up. Would like to know what PSI you are running. Have you cleaned the grounds for the fuel pump?

[irish]

40-55 PSI when running, haven't cleaned the grounds but sounds like a good idea now that you mention it. I'll probably end up taking off the bed to further investigate the fuel pump, I'll have to remember to do that.

[lesterl]

yeah the 45 is suspect.

[irish]

well i finally broke down and put in a new fuel pump... no noticeable difference. ran some injector cleaner though it too, no help. replaced the ignition coil, also nothing. when the truck starts up you can barely hear the pump, but after a few min it starts to get much louder. also, during normal operation the fuel pressure will rise a little to 60 psi under load. after a while it stops doing that, and shortly later begins cutting out and eventually stalls. usually starts right back up though... out of ideas here

[Jaxom]

I'm no expert, but just from what you've said, have you thought to check the wiring harness for the fuel pump from the pump all the way back? Could there be a frayed/pinched or other wise bare wire causing a short?

[infinity96]

My buddy has a 94 or 95 model s10 with the 4.3 vortec, And he too complained about his cutting out and him being able to reach under the steering wheel and wiggle the main wiring harness plug and it would fire right back up. He finally found that the screw that holds that connection tight has backed out. He tightened the screw and has had no problems with it for the past 2 months.

[irish]

appreciate the support guys. i hooked up an ammeter to the fuel pump circuit and its pulling a fairly solid 7.5-8 amps with no dips. i noticed when the pump starts whining louder it pulls a bit less current which leads me to believe the pump is cavitating (bad gurgling noise also). during this time the idle fuel pressure is OK (50 PSI), but it wont rise with engine load--sits at a steady 50 psi instead of ramping up to 60 like it normally does.

another nice thing i just found out, upon replaceing the fuel pump i realized that this isn't the original fuel tank/sending unit. there a big "1992" written on the top of the gas tank in grease pen and the fuel pump harness wires were TWISTED TOGETHER AND TAPED!! there's also a bunch of crud stuck to the inside of the tank that looks like rust but wipes away like dirt which apparently destroyed my fuel filter (which i also replaced)... looks like i might need a new tank now too.

that said, i've gotten pretty much nowhere with this. the problem is actually worse now than it was before. the fuel pressure is still too low and i can't drive it for more than a couple minutes before it starts whimping out, although its generally doesnt stall.

[irish]

Just in case anyone was interested how this all ended:

Gas tank contamination was clogging up my fuel pump and causing the impeller to cavitate and lose pressure. I ended up replacing the fuel tank, pump, filter, and injectors as the contamination had spread to most of the fuel system--runs great now.

-New gas tank from rockauto.com: $140
-New OEM fuel pump from gmpartsdirect.com: $600 @&#%!
-MFI upgrade kit from gmpartsdirect.com: $240
-Fuel filter from advance: $12

Total: $992

Lesson learned: Gas tanks from the junkyard are bad news.

[MrCallaway]

well congrats on gettin the truck fixed... kinda of a large bill, but hey at least you dont have to worry anymore!