Sorry, I
JoeIsuzu wrote:
Wow, it should go 65+, maybe even 75 (max, not cruise).
Oops. I think 75 would be a fantasy, I forgot you said 4-speed AND 4.10. The '86-'87 P'ups had 5-speeds, and they should do 75...and 65 is more typical for the 4-speeds. But 50 isn't right.
I went several years with a problem on mine that affected the highway performance. It seemed fine in stop-and-go driving, but it didn't want to go 65 on the highway. Considering it's 2wd and 5-speed, that's really bad. I tried several things to diagnose it for a few years (I even dropped the fuel tank and inspected it for debris). Finally, on the advice of someone on the IsuzuPup.com forum, I removed the Cold Start Device. This is designed to advance the injection timing for cold starts. I was skeptical, but I'd tried everything else. After I removed it, the truck drove like new. My fuel economy went up significantly, too.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com