check engine only when towing

[clintryplug]

I have a '94 Isuzu P'up (4 cylinder) that the check engine light comes on only when I'm pulling my small 14' fully rigged aluminum Jon boat (700lbs gross load with trailer). More specifically it really only does it when I'm on the freeway (up around 60-70mph) and even more specifically when I press the accelerator. As long as I have the accelerator pushed (at these speeds) it stays on but the second I take my foot off of the accelerator the light goes off then again comes back on when I depress it again. I've been pulling this load for a couple of years and have not had this happen until recently, I know a 4 cylinder p'up is not your ideal towing vehicle but I would think that 700lbs shouldn't be too much for occasional towing. The light doesn't come on at all when I'm not pulling the boat. Any ideas?

[quaddriver]

well, Id scan it first before forming any opinions

[DJJC]

it could be that the engine is getting a little hot. depends on the ambient temps, aerodynamic load of the trailer setup, fuel quality, road temp...and so on

[Hemi99]

I can only think that it would have something to do with engine load. It could be that at those speeds, and the john boat having the aerodynamics of a box, are causing the engine to be under a severe load. It may hurt it but it may not, could just be a "feature" of your truck. Just my 2 cents....

[quaddriver]

btw - a 14ft jon should weigh in over 200lbs empty, depending on what 'fully rigged' means, that 700lbs would be just the boat.....what about the trailer? Im thinking at LEAST another 300 there for bare minimum....

[clintryplug]

700lbs including the trailer. the boat empty is about 200lbs but fully rigged (outboard, trolling motor, batteries, electronics, ply wood casting deck and flooring) brings it up to about 500lbs then add 200lbs for the trailer.

[MagicRat]

Definitly scan the computer for codes.
Given your description, I'm thinking throttle position sensor, manifold absolute pressure sensor, or knock sensor.
It's a long shot, but a tankful of premium gas might help this situation.

[Cait Sith Cat]

It's a '94... it doesn't have an OBD link.

[jimmy[the]gent]

this occurs because i think you might have over the years lost engine compression or a gasket somewhere in your engine is worn, culd also be your pistons and engine block arent wat they used to be and they cant handle a load put on them in time wat will happen is when you put stress on your car like even going up a hill will make your car rock back and forth i predict engince work will be neccesary for your car in the future

[curtis73]

Originally Posted by Cait Sith Cat

It's a '94... it doesn't have an OBD link.

sure it does. Its just OBD1. Hit up a local parts store chain and they'll read the codes for free. Most cars past 1987 have some form of diagnostics. Some are intensely remedial, but some have anywhere from 4-30 codes.