my 1989 gmc s15 just started to suck gas bad.


Asked by Feb 02, 2017 at 07:46 AM about the 1989 GMC S-15 Extended Cab SB

Question type: Maintenance & Repair

1989 gmc 4.3 mpgs dropped bad. lost about 40 -50 miles per tank. nothing
done before that started. was running ok, had a rough idle but was getting
decent mpgs. so far i have replaced the ignition coil and egr valve, but after
replacing egr valve it started to sputter at take off. egr purchased at
autozone. dont want to start replacing parts. so if you guys have any
pointers, they would be very appreciated.

5 Answers


Many times the O2 sensors get slow and weak with age and can cause a big loss in the mpg department. Normally they should be replaced at 100,000 miles. Now don't run out and buy O2 sensors just yet. If it was me I would have your truck scanned for fault codes. I think your truck has throttle body injection and there could be an issue with the fuel injector. Report back with any codes that show up during the scan.

1 of 1 people found this helpful.

Will do that, but if the o2 sensor was bad, shouldn't I get a check engine light , thank you


Normally yes it would light the CEL. I would still have it scanned as some codes can be hidden. How many miles on this truck and what engine?

1 of 1 people found this helpful.

158k , 4.3 V6


follow up on y 89 gmc s15, with 4.3V6. replaced egr valve and started to sputter, replaced o2 sensor and started running good, but as soon as it warmed up it sputtered again on take off. Installed old egr valve and sputter went away. replace fuel pump just cause of the high miles and im not sure of the history of the truck. runs good but still seems to be burning more fuel. no cel and driving me F#@(ING nuts. any suggestions will be very appreciated. thanks

1 of 1 people found this helpful.

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