1989 gmc s15 pickup gives only 12 miles per gallon

[vikasintl]

We recently bought this 1989 gmc s15 which has 112000 miles.
Changed spark plugs, changed tires after bought it...added fuel cleaner and heet for possible water in fuel line...

what brand of spark plug wires,distributor cap/rotor and air filter we should buy?

what else we should do to improve the fuel economy...I checked it should give approx. 20 but this one gives only 12...

its looks like on low rpm (when we run from idle to up to 10 mph) its has low power...

what is the solution?

[Tink]

What motor does this have? 2.5L, 2.8L or a 4.3L? Is the service engine soon light on?

As far as tune-up parts, I stick with AC delco on most everything but the wires for wires, I prefer Taylors.

[Myself]

I would guess the fuel pressure regulator spring in the throttle body is broken. I've replaced them several times with springs you can buy at the local hardware store. Or you can buy a whole new regulator. Since you have to remove the throttle body to get at the regulator anyway, you might as well rebuild the throttle body and clean the injectors.

[vikasintl]

Originally Posted by Tink

What motor does this have? 2.5L, 2.8L or a 4.3L? Is the service engine soon light on?

As far as tune-up parts, I stick with AC delco on most everything but the wires for wires, I prefer Taylors.

Thanks...its is automatic 2.5 L and 4 cylinder ..no service engine soon light is not on...

[vikasintl]

Originally Posted by Myself

I would guess the fuel pressure regulator spring in the throttle body is broken. I've replaced them several times with springs you can buy at the local hardware store. Or you can buy a whole new regulator. Since you have to remove the throttle body to get at the regulator anyway, you might as well rebuild the throttle body and clean the injectors.

Thanks..I will check and let you know...

[vikasintl]

Originally Posted by Myself

I would guess the fuel pressure regulator spring in the throttle body is broken. I've replaced them several times with springs you can buy at the local hardware store. Or you can buy a whole new regulator. Since you have to remove the throttle body to get at the regulator anyway, you might as well rebuild the throttle body and clean the injectors.

Well I tried today..but spring is not broken...and spring has some tension ..have no idea how to confirm whether the tension is enough or not? or I guess it does not matter...as long as spring is not broken, we should be ok right?

any other tips of low fuel economy? oh btw timing light was jumping all over instead staying steady, at mfg. specification under the hood...

does it give you any idea?

[Tink]

Did you disconnect the EST? It is under the dash on the passenger's side... you'll need to disconnect that to set timing.

[vikasintl]

Originally Posted by Tink

Did you disconnect the EST? It is under the dash on the passenger's side... you'll need to disconnect that to set timing.

I put a jumper between a and b terminal and check engine light was flashing..so it was in set mode...

[Myself]

If the spring is not broken you're OK there. Timing jumping everywhere is usually a worn out distributor or sticking advance mechanism. Have you put in a new fuel filter? Are your plugs gapped correctly?

[vikasintl]

Originally Posted by Myself

If the spring is not broken you're OK there. Timing jumping everywhere is usually a worn out distributor or sticking advance mechanism. Have you put in a new fuel filter? Are your plugs gapped correctly?

Fuel filter looked clean so I did not put a new one...I guess they are costly...

btw how do you clean fuel injectors?

Plugs are brand news AC delco..

I can check distributor but not sure how to check sticking advance...

Btw I checked again still timing is not steady at 8 ...it still jumps ...even though after correcting vacuum leak and replacing spark plugs.. it idles and runs smooth...



what else could be culprit?