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Old 06-08-2018, 04:02 AM   #1
Join Date: Dec 2013
Location: Palm Desert, CA
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Vehicle: 1989 D21 VG30E
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Default VG30i 1989 D21 4x4 - Idle hunting, rough, +-100 - Solution, Fixed

I just had a nightmare of a time fixing what ended up to be a very cheap and simple fix. I'm outing this here so others may avoid the costly process I followed.

It all started when I was losing top end power. I had thought the woodruf key on crank sprocket had loosened and wore timing out a few degrees. So I tore it down to inspect. All looked good but I went a head and replaced the sprocket, idler and belt.

No change in power loss. I went to ignition electrical. Found the rotor was scorched on 2/3rds on the advance side. Replaced rotor. Everything seems,back to normal now, most power back etc but still some idle hunting.

I figured I'd treat my truck to some gumout brand injector cleaner in the gas tank. I added the proper dose for a full tank, then filled the tank.

When I reached 1/2 a tank it started to run like shit. Knowing the timing was fresh, ignition rotor fresh. I did a,seafoam soak via brake booster vac line. Also used gumout on the throttle body. It got worse. Far as I can tell the gumout spray smoked my MAF. Confirmed it was outing out upwards to 9volts. Replaced it, it again ran at least but now back to running like shit but drivable.

I replaced the TPS because thought mine was bad, then it, got deffinatly bad when I cracked the board opening it up to clean it. I cracked the graphite trace, so it was dead in 20% of the zone. I actually fixed it with filling the crack with pencil lead just by drawing in the crack. It actually worked reliably on the bench so I put it back in. Uneasy with the pencil repair I ordered a new one and replaced it. New TPS and adjusted.

All wire joints under hood cleaned and tested. I star growing parts at it.

New distributor
New wires
New Coil

I start looking at injectors. I do balance test. Both still have idle hunting.

After about 2 weeks. I find my fuel pressure gauge. 25 PSI. Confused because this is a new fuel pump a year old. Replace the fuel filter, no change.

So I drop the gas tank and don't see anything abnormal other than some slight debris on the filter. I ,clean everything up and reassemble. Fuel pressure is now 37PSI cool that just have been it. Wrong. I barley got my tach set up to set idle when psi dropped and idle huning started again.

I've never seen a pump have reduced flow, usually there just dead or work. But I figured maybe some fins broke or something.

New fuel pump. Drop tank again. Removing the fuel pump, I pull on the leader line and it opens up a crack. @$#!&*%#!!#$. A pressure side fuel leak in the tank....

That explains why it showed up when at 1/2 a tank, why it was loss of power under load, why it was idle searching etc.

Basically all the shit I did the only thing that needed replaced was a dis rotor and 50cents of gas line.

I suspect the injector cleaner weakened the hose making the existing crack worse.

Also this hose issue explains why the rotor was scorched. The ECU was constantly trying to advance to correct fuel mixture from the under fed injectors.

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h.stickeye (06-08-2018)
Old 06-08-2018, 04:18 AM   #2
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Location: Brisbane AUSTRALIA
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And I've been meaning to replace all the bits around my fuel tank too! Timely reminder really for all trucks that are near on 30 yrs old. Thanks for the writeup.
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Old 06-08-2018, 10:16 AM   #3
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Vehicle: 1997 D21 King Cab XE 2WD, 1998 Pathfinder.
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Go on a complete hose-replacement program by stages. This week THESE hoses and better clamps...the next week THAT set. Buy hose by the foot that matches what you have now. Use better clamps and don't overtighten them.

1997 King Cab XE, 5-sp, canopy, AC/PS, KA24E, 115,000 miles. Need a technical manual? Drop me a message. Chilton's for amateurs.
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