Have a question for a friend...

[bigblock73]

I had this gentleman E-mail me at my 73-87.com address, and he had a question that I cannot provide an answer for. Can any of you help?

I am going to e-mail him this link, hopefully someone here will have some ideas and provide him his answers. Thanks

Good day to you Jeff.. My name is Roger and I am writing to you to see if you know of this problem happening to anyone else. ( I will try not to ramble on too much ) . I have owned this 87 GMC Wrangler pick-up for 3 years now, had a very hard time passing the E-Test this year and 2 years ago.The problem with this truck is fuel milage--- 85 percent of the time I am getting between 5 and 6 km/litre. Every now and then after I hit a nasty bump or a very rough set of RR tracks, my fuel milage will jump up to 8 or 9 km/litre ??? We have scoped the system and cannot find the problem, changed sencors, changed the computer, even said a little prayer but to no avail !!! My wife and I do a lot of camping and quading. This involves carrying a 500 Polaris and our gear in the truck and pulling a 17 ft house trailer through some very hilly terrain.( Parry Sound , Ontario ) On our latest trip , I was getting 7.7 km/ litre. Pretty good , and then we hit the RR tracks in a small town and there went the milage !!! Down to 4.5 for the rest of the trip... I constantly monitor my milage as you can see. ( Note--- when getting the good milage , the truck does not run any hotter then normal ? ) Strange But True . If you have ever heard of this before or know of a cure , I would sure be happy to hear from you !! P.S. I have only gotten part way through your web-site so far and I have to say that you are doing a very good job with it !! Take care , maybe we will talk later , Roger , from Woodstock , Ontario , Canada..---

[Mike76251]

Hit a bump and change the mileage?
I would doubt that is possible.
If the engine has the same power output "pre-bump" and "post-bump" the fuel consumption would not change.

Tell the guy to plumb in a graphing flow meter on his fuel line and go find some rough railroad tracks. Then report back.

[swervin ervin]

Possible or not, there are things on these trucks that go wrong we sometimes find hard to explain. One was the bumping/popping I had on my truck. I finally found out what it was after my upper control arm bolt broke.

When someone explains stuff like the guy did, I have no reason to doubt he has the problem. It sounds strange for sure but that don't mean it can't happen. With the way he says it does, I would think there is something loose and comes and goes from the jar it gets. With the mileage decrease/increase, first thing I would think of would be the throttle body. The TBI's are pretty simple as far as moving parts. My first thing to do would be to pull the throttle body off and start checking for loose parts. I would do a good check on the injectors first. Another thing I guess is possible could be maybe the gas tank is full of rust and crud moving around.

Stuff like this can drive you crazy. You can tell others what is going on and they won't believe you but you know for sure it is happening.

One question I have is when this happens, as in mileage getting worse, does the power and drivability get worst too?