Hello,
I am new here and I would first like to say what a great place. I have an 88 Hardbody extended cab that my Dad gave me. He was the original owner. He wanted me restore it. It needs a little body work, nothing major, rust mainly. It drives very nice and the engine runs good. But I have noticed that at a certain RPM is get a diesel sound. If I hit the clutch and blip the gas. It does not do it. Its only really noticeable 1st to 3rd gears. Any ideas what it might be? Its got the Z24 engine with 128K on it. It runs good. I have no problems with throwing my CR500 in the bed and taking off for the desert. Thanks in advance for any help.

Rob

Sounds like detonation, or "pinging". This could be caused by timing too far advanced or low octane gasoline.

The cheapest and easiest thing to try is to run a tank of premium gas through it and see if it goes away.

Thanks for the reply. I try to run Shell Premium always. Its still does it. Before my dad gave it to me he had Nissan mechanic go through it. My folks live at 4500 feet in Northern Cal. I live at 2200 in Socal. That much change in elevation should not have that much affect would it? If it was detonation wouldn't it happen even with the clutch engaged? If I have the clutch in and hit the gas the engine sounds nice and smooth. When I let it out and get about half throttle it does it. It almost sounds like an annoying rattle. I am going to change the oil in it today...going to dig around a little. Thanks for your help thus far. I use to know all of this stuff. I have forgotten most of it. Been doing nothing but rebuilding jet engines for the past 14 years. Not much car maintenance in between.

Did those engines have any problems with the exhaust manifolds?

-Spike

I have the same truck/engine combo,nearly the same mileage. I had the timing cover off to replace the leaky main seal and found that the timing chain tensioner assy was coming apart and the chain was pretty loose. One of the legs was nearly worn through. I replaced everything, chain, sprockets, tensioner assy while I had the cover off. it's nice and quiet now.

I worked on the truck for a while last night. Changed the oil/filter, and bunch of cracked/weathered vaccuum lines. I went to pull the plugs and some were a little whiter/lean than my liking. I did take some chem-tool and srayed around the intake manifold/head junction and also around the Carb base gasket. I was hoping I would find an airleak. That way I could change the gasket and be done with it, hopefully. No previal, no change in RPM. Is it possible for my Carb to be the culprit. Or is there something else I should check first? Shouldn't the Carb automatically compensate for the altitude change? I only ask because I see electrical plugs going to the carb. Thank you every one for you help and inputs.

Rob

do you have to manually adjust the valves on the older 4 cyl's?

That's what I was thinking. Adjust the valves, and maybe check the timing chain.

i knew a guy that had a 86.5 hb 4cyl, he said he had to take the head cover off periodicly and adjust the valves, that sounds like it could be the prob.