Fuel problem on '90 S15 Jimmy 4.3 4WD


jeffstone1960
07-22-2004, 12:51 PM
I am having Fuel problems with my S15 Jimmy. When I depress the pedal it feels like it's getting fuel starvation and almost stalls unless I release the pedal. It idles just fine.

The problem has progressed to the point that I can barely get the truck to move without it wanting to stall.

The two injectors in the carb are spraying a nice even cone.

I've replaced the Throttle position Sensor, The O2 Sensor and the EGR valve.

When a fuel pump goes out it just quits period, right? This model has a fuel pump relay that I will try and replace next.

Thanks for any help you can give me!

Teaman3
08-27-2004, 02:29 AM
Fuel pressure failing maybe.
Check the Air pressure sensor. Seems as if a vacuum spike is happening causing over advancing and/or fuel over enrichment. Does the hesitation happen if you slowly open the throttle ?

jeffstone1960
08-27-2004, 02:35 PM
It will rev up if I slowly apply the pedal but only to a certain point. Then it wants to cut out anyway. I replaced the fuel pump. Originally, we had major problems getting the distributor back in the right position. At TDC , #1 was pointing between 5 and 6 o'clock (closer to 6). But when I went to time it I ran out of room just before the mark with the cap turned as far clockwise as I could get it. It ran just fine for a few months though so I left it. Then this problem began and has gotten progressively worse.

I'll check the air pressure sensor (it's location?) and am also going to try and time it again. Wild stuff! Never had a problem with this car until a friend talked me into replacing leaky valve seals. I could live with a 1/2 quart of oil a month over this! The engine has close to 260k on it and still runs strong (normally). Duralube and Slick50 go in every third oil change. :D

Thank you for your reply

==================================================
Check the Air pressure sensor. Seems as if a vacuum spike is happening causing over advancing and/or fuel over enrichment. Does the hesitation happen if you slowly open the throttle?

Teaman3
08-28-2004, 05:41 AM
You're welcome.

The Air pressure sensor (MAP) is probably mounted on the side of the air filter pan. It has a vacuum tube connected to it and an electrical 3 or 4 pin connector.

While you're at it check the TPS output for a smooth increasing voltage. Might have a worn resistor band or wiper lifting off as it turns.

What you have described above about the distributor makes me think it is not set up correctly. Either the rotor shaft is out a notch or the HT leads are out a connector post.

What size engine is it ? The 4.3 had the No 1 HT post shifted, around 1988, by one post:

1987 No 1 @ 7 o'clock
1988 No 1 @ 5 o'clock

As you face the engine:

Even cylinders left bank 2, 4, 6 front to back.

Odd cylinders right bank 1, 3, 5 front to back.

Firing order: 1, 6, 5, 4, 3, 2 clockwise

At TDC, compression stroke, the rotor should point more or less to No 1 HT post

The 2.8 cylinders are:

Odd is left bank 1, 3, 5 front to back

Even is right bank 2, 4, 6 front to back

Firing order 1, 2, 3, 4, 5, 6 clockwise

No 1 HT @ 7 o'clock

The distributor cap lugs should be at 7:30 and 1:30

If you have to remove the distributor to reposition, remember that the rotor shaft gear will move the rotor round 30 or so degrees as you lift up/put it down in the hole. There might be a hexagonal shaft loosely fitted on the end of the rotor shaft, so shake the distributor as you lift it to make the hex shaft drop off. If it comes out, you'll have to fiddle it back in, pretty much by feel.

There should be a label (VECI) on the slam plate/ radiator cowl telling you the timing requirements. The ESC has to be disconnected I think.

Check that your vacuum lines are gas tight. Leaks in them cause the mixture to weaken as the throttle opens.

Let me know what happens.

Enjoy !

jeffstone1960
08-28-2004, 03:19 PM
Thanks!

Gives me a lot to go with. I've already resolved to re-install the distributor to see if it helps.

I'll get back to you on what I find. Probably won't get to it until about Tuesday this week.

I ended up buying a Jeep Laredo cause I didn't have time to fiddle with it. The jeep has a 4.0. I like both these SUV's but the Jimmy definitely has more beef when it's running even fairly well.

Teaman3
08-28-2004, 06:24 PM
Ok. It's best to do one thing at a time, so when it's done right, it can be knocked out of the fault loop.


:o)

Teaman3
08-28-2004, 06:28 PM
Just remembered: Checked the VECI label on my Jimmy. Doesn't look like the ESC is disconnected. Instead there's a wire (Tan/black stripe) broken out from the loom in the passenger footwell that is disconnected. Check your Jimmy's VECI label though.

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