'94 Isuzu trooper with 158k miles

Hello, I'm a new member. My dad does forums a lot for his Internationals, so I thought I'd give it a try too. :)

I purchased a 94 Isuzu trooper over the summer at about 150K and now have 158K on it. Recently I have been getting a check engine light that comes on intermittently. It first occurred after driving HWY for about 1.5 hrs, but than did not show itself for another month or so. Primarily my driving has been in-town for less than 2 hrs at a time. More recently I've noted that the light has been coming on more frequently. It is on while driving, and goes off when I am idling at a light. Additionally, my gas mileage efficency had dramatically decreased. Please advise on what you suspect may be the issue.

Also, I am due for an oil change very soon, but the pressure gauge maintains itself from 30-55 lbs/pressure. I have noted that reading the dipstick is difficult for me as the color of the stick is too close to the color of the oil...

And for another bit of advice seeking, my Trooper is also due for a Transmission flush. I've been warned about that though because I've been told that putting 'clean' fluid into an older transmission can cause failures. Is this true? And, if so, what would you suggest I do for my flush?

I am looking forward to anything that one might have to say. :) Thanks for reading!

Welcome to the Isuzu world.

In regards to your Check engine light, maybe someone can chime in on how to read the codes on trucks prior to 95, mine is a 97 and I know Autozone will read codes for free on the OBDII, but you have the OBDI.

I'm not quite sure what your question is regarding your oil, but your psi sounds about right.

Regarding your transmission, you are correct, do NOT let anyone convince you to flush your transmission AT ALL. I highly recommend having someone, or yourself, drop your tranny pan, change the filter and gasket and replenish around 5qts of new fluid. This way you can see what condition your tranny is in, if previous maintenance records are unavailable or skeptical.

I have 188k original miles on my auto tranny, with partial ATF fluid swaps every 12k miles.

Too much new fluid CAN be detrimental if the tranny has been neglected.

Your auto tranny IS the GM 4L30-E which does not handle neglect, abuse, or leaks very well at all, it is known for burning quickly if ATF is low, old, or in the wrong gear for serious mountain driving.

I very highly recommend ATF partial fluid swaps every 12-15k miles on this transmission, and change the filter every 30k.

I have been dealing with the check engine light on my 94 trooper as well...it seems to come on when on the highway then off when i get off the highway...once it does come on my truck runs bad going up hills or when i give it gas.....does that sound familiar,? have you had any luck...so far I have
changed cat converter
changed EGR
cleaned injectors
changed fuel filter
cleaned maf sensor
changed o2 sensor

still hasent fixed the problem.....ill let you know if i fix it, please let me know how you make out

Mandex....not too many people ever reply back..check out planetisuzoo.com, you'll get MUCH better help and responses.

I've been a member here for a while, this board is nearly dead now. Use to be real lively, but 90% of newbies never respond back, so most of us ole-timers have just about given up.

Fast forward this reply to 2014...
Here I am re-reading this and wishing to high heaven I remembered this! Somewhere in the not too distant past I let a pushy mechanic flush my tranny (at over 200K) and guess what?! - yep, it dislodged all that gunk and now ...
Well, I asked another garage to drop the pan because I had a flashing 'check transmission' scare and they found metal shavings, a lot. They don't know if my clutch gears have a few months or a year ...
But, combine that with the leak somewhere in my transmission case ... (it makes me want to cry)