88 Trooper Engine Knocking

[James1226]

Hi, I have a 1988 Isuzu Trooper II with 99,000 miles; the Trooper has a 2.6L 4 cylinder engine (model 4ZE1). I bought the Trooper nearly 12 years ago and only put 400 miles on it; (at the time it ran flawlessly) it was then garaged. Recently I have taken it out of the garage in hopes of using it again.

When I first took the Isuzu out of the garage the fuel pump was dead, which seems to be a common problem. I replaced the fuel pump along with fuel filter and it started the car. It started fine; however, when driving the vehicle when ever the throttle is depressed any more than the slightest bit it begins to knock (Ping).

In an attempt to fix this problem I checked and adjusted the timing, the timing was at 6º BTDC; I adjusted it to the factory setting of 12º BTDC; which of course increased the knocking. I then proceeded to put in new spark plugs (NGK), and a new air filter. I also checked that the plugs were receiving a spark. Again the engine knocked when ran.

I later put in medium grade fuel (Higher Octane), and a fuel system cleaner. Neither of these have had much chance to clean the fuel system due to fear of ruining the engine by running it, though they have not seemed to change anything as of yet.

During this time period I also checked the self diagnostic system of the Trooper; upon the first test it gave a 6-1 meaning that there is a short/broken hot wire in the harness to the MAF. However after disconnecting the battery in order the clear out the ECM's memory and take a short drive down the road this error message has yet to reappear.

So I am now running out of ideas in order to diagnosis the knocking that occurs under throttle. Finally recently upon starting the Isuzu Trooper it goes to a high idle then stalls after a couple seconds, it may do this up to three times before staying at idle without stalling. The idle also appears to be somewhat rough compared to other automobiles.

In summary the engine is knocking, (pinging) has a somewhat rough idle, and sometimes stalls upon cold starting.
I have: Changed the spark plugs
Checked the spark
Timed the engine
Used higher octane fuel
Used a fuel system cleaner
Checked the diagnostic system

Thank you in advance for any help or suggestions.

James

[Ramblin Fever]

Are you saying this truck was only ran for 400 miles, 12years ago?!

Could be any number of things if it hasn't been started for 12yrs.

Have you changed the oil/filter? Probably needed done prior to starting it, if that oil's 12yrs old, it for sure has a lot of moisture in it - this could cause issues.

[James1226]

Thank you for your reply Ramblin Fever; the oil pressure, level, and appearance where fine, prior to, during, and after the first running, hence I did not change it. However, per your suggestion, I drained the oil and installed a new filter; sadly this did nothing for the problem. In my time since last posting I also changed every vaccum hose/line, this also did little (The replacements made the idle slightly smoother). I also verified TDC and it was correct, officially eliminating the timing of the engine as being the culprit to the pinging/knocking. Tomorrow, I hope to check the fuel pressure and return; I will update the thread with those results. I am hoping that I find something soon; this is beginning to turn into more than just a little fix-me-up.

Thanks in advance for any help and/or suggestions.



James

[James1226]

Since last posting I tested the fuel pressure and it was high. Because of this I order and installed a fuel pressure regulator which fixed the high pressure problem; however, to my disappointment this did not fix the pinging/knocking problem.

I am approaching, if not already at, a loss of ideas; therefore, more so than ever, any help, advice, or suggestions would be greatly appreciated. Thank you for your time and consideration.

James