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'90 1/2 ton issues

1K views 10 replies 8 participants last post by  bow-tie-boy 
#1 ·
I have a 1990 1/2 ton 4x4 with a TBI 350. A few months back I was pulling my trailer that had a ground in it that I didnt know about, and would blow fuses when I would use the turn signal and step on the brakes. Well the only fuse it would blow was for the brake lights, no big deal, replace the fuse and dont use my blinkers, and fix the ground when I get home.

well I am not sure if this caused my problem, but I was in reverse (backup lights on) and using the brake when I heard a pop, no big deal right....change the fuse again and be on my way.....well it wasnt a fuse:( ever since my speedo is stuck at 34 MPH, and the service engine soon light comes on an off whenever it feels like it. Not to mention you can smell gas like crazy. So she is running really rich, which would explaing my worse than normal gas mileage. the motor only has about 7k on it, and since this happened the truck feels a little more doggish. could just be in my head, especially since it starts right up and idles/runs fine.

so could I have blown the computer? does the speedo get controlled my the computer? I am sure the fuel/air mix is. would the truck run if the computer is f'ed up?

It still runs great (other than the gas smell), I plowed with it all winter, and made several hauling trips with it, just never noticed the strong fuel smell till the weather got nice out.
 
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#2 ·
It is possible that you did blow the computer, get it to your local parts store that will do a free scan. It could have lost the ground in the computer and or the ground to the O2 sensor in the computer causing the shitty gas smell/mileage.
 
#3 ·
thanks KB, but how would I lose ground, that night when the trailer was hooked up? it was fine before that, it just happened that night due to a bad trailer ground. :confused: all was fine going to the event cuz it was daylight (not using headlights) it was when I went to leave for home (dark out) that I started having the problems.

especially since my speedo is stuck at 34.....all of the other gauges work, just not the speedo (dont have a tach)

as for the o2 sensor, I will have to look into that...not sure I have one. when I re-did the exhaust, I dont remember replacing that, unless it is on the downpipe, I had the exhaust custom bent from the downpipe back with no cat, and just cherry bombs. so there is no place for an o2 sensor.
 
#6 ·
I would look in to what circuits are affected in relation to the turn signals, brake lights and reverse lights. Then figure on those circuits what could have blown compliments of your short from the trailer.

I would first follow Killer B's advice and be a little smarter about using that trailer again until fixed!
 
#8 ·
ok, finally got a chance to look at this, and found a pinhole in the fuel line...when the truck is running, there is a solid stream of gas coming out.....so gas smell/shitty mileage solved

what about the speedometer being stuck at 34? :confused: I have checked all fuses and they are fine. speedo worked fine up until that night when I started blowing fuses, so I dont think it is the cable and/or speedo gear. unless these things had a speed sensor?????
 
#9 ·
i know my 93 had electronic speedo but I for some reason think it one of the first years for that. roll under it and look to see if it has a cable speed sensor or both.
 
#10 · (Edited)
If it has a speedo cable, the sensor is behind the dash. It is a light emitting diode that just sends the computer a signal. The speedo gauge should still work as it is a similar mechanical set up as in older models. I suspect the speedo gauge itself is just stuck. The cable turns a piece that rotates around a wheel that the actual needle is fastened to. As that piece rotates, it causes the inner piece to move indicating the correct speed. I've seen it where a good bump, jolt, or dirt will make it stick. Remove the clear plastic and move it with your finger a little bit to see if it returns to zero. If it doesn’t there is a little spring that probably broke which may be making it hang up.

If it's new enough that you don't have a cable, I believe the speedo gets an electric signal from the sensor in the transfer case. That signal is somehow converted to an electric motor which turns the needle and that motor probably went bad.

Depending upon the year, it may appear that you don't have a needle but a gauge that moves up a scale. I believe that once the clear and colored plastic is removed you will see that is still a conventional speedometer head.

I haven’t worked on one of these for awhile now so I’m pulling this from what’s left of my memory. Hope it helps.

RD
 
#11 ·
if it's a 90' it will have a VSS, Vehicle Speed Sensor. Check your compter for the Trouble codes and see if a 24 pops up. That would be a VSS fault. If that is the case start chasing wires and checking connections, cause that sensor will be around $75 to $100 to replace. If your lucky it will just be a break in the wire or a loose connection.
 
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