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1994 Isuzu Trooper
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Discussion Starter · #1 ·
Hey folks,

I'm finally learning engines (suspension guy) and gradually chasing down an issue with my 94 3.2 SOHC. The engine has been bogging out when I snap the throttle at low rpm and wants to die/kind of backfires. as if it's either getting too much air or not enough fuel. I've replaced a few parts and done some work along the way:

-had a seized up/slow to adjust IAC valve and swapped that out.
-code 33 for MAP and swapped that out.... no improvement, but it doesn't throw that code anymore.
- discovered oil in a couple of the spark plug wells, so did the valve cover gaskets and new plugs and new wires... a bit better, but still embarrassing when accelerating from a stop light and definitely terrifying when accelerating from a stop headed uphill.
-Pulled the bloody plenum back off again, pulled the injectors and flushed those out and replaced every vacuum hose that I could get my hands on... way better, but still no where close to being safe in traffic.
I should add, the FPR holds vacuum and coils meter out good.


I finally did today what I probably should have done before any of this... I got myself a fuel pressure testing kit. The only reason I didn't do it earlier is because the fuel pump was replaced only 3 tanks of gas back. However, running pressure is just exactly 20psi on the rail. I can't find anywhere what the pressure is supposed to be, but that seems mighty low to me. Seems like it should be roughly double that.

Anyhow, before I go and drop the fuel tank and chuck in a new pump, is there anything else along the way I should be looking for? What is the psi supposed to be at? What is the best pump to go with? I'm just trying to keep this thing limping along until the winter and do an r2.8 swap. Help me go camping until then!
 

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You will need 40 psi at the absolute minimum to make the truck run so I'd go ahead and replace the pump. Just make sure the inside of your tank looks good. I like Bosch fuel pumps but as long as you don't buy cheap crap you should be set. Make sure to get the strainer sock if the new pump doesn't come with it and change the fuel filter as well.
 

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42PSI is the operating pressure. If you have less than that don't automatically condemn the pump. The fuel system on this vehicle consist of more than 7 parts and they are all suspect of failing.
 

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Shawn is basically saying to check the fuel filter and pressure regulator as well. (plus voltage at the pump). You can easily test the fuel pressure before the filter, just be prepared to get gas on your clothes.
 

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1994 Isuzu Trooper
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Discussion Starter · #5 ·
42PSI is the operating pressure. If you have less than that don't automatically condemn the pump. The fuel system on this vehicle consist of more than 7 parts and they are all suspect of failing.
Thanks Shawn.

What else would you be looking at?
Shawn is basically saying to check the fuel filter and pressure regulator as well. (plus voltage at the pump). You can easily test the fuel pressure before the filter, just be prepared to get gas on your clothes.
Right on. Thanks a bunch, guys. I'm eager to get after it and this gives me a lot more confidence.
 

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1994 Isuzu Trooper
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Discussion Starter · #6 ·
Solved! And an easy fix to boot! I did what you guys said and took a pressure reading before the fuel filter. Got gas on my clothes. Same thing... 20 psi. The last thing I suspected was the fuel pump, given that I just had it towed to a reputable shop a couple months back and they did the pump. I cut a hole through floor for access, because I obviously have a full tank, and pulled the pump. The first thing I noticed was that the rusty phillip's head bolts that everybody complains about were really easy to back out. Like, a bit more than finger tight. Like, there's no possible way it was making a seal with the gasket. Next I pulled the pump out of there to discover that the tank is completely spotless and the sock is clean but, the rubber hose that connects from the pickup to the pump is just freely sliding up and down, hardly connected at all and doesn't appear that the hose clamps had ever been tightened. Anyway... I corrected all of this and it now runs perfect(save for a bit of valve tick of course). Better than ever. I don't regret doing any of the other work, just the redundancy in the order of operation. I'll sort out the floor tomorrow morning and fab some kind of sealing hatch. And just a heads-up for those rusty phillip's head bolts on the outside of the tank: I was a bike mechanic years back and took one look at those threads and knew it was an M5, of which I've horded many hundreds. Any bike shop will have heaps of them and it was far easier to use a 4mm hex wrench to get a good seal on that gasket.

Thanks again fellas!
 

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1994 Isuzu Trooper
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Discussion Starter · #8 ·
Nice work. Let us know what you do for the hatch. How did you decide where to make the cut?
You bet. I got the frame of the hatch welded up today and I'll make the cover tomorrow and post a few pictures and measurements as I go. Stay tuned. And thanks again.
 
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