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Fuel Injectors Won't Start

I have a 1991 fuel injected Isuzu PU. I have spark, I have gas (replaced the fuel pump already) and yet when I go to start it it cranks and nothing happens. A month ago it use to take several attempts to start it, but once it started it would run fine. But once you turned it off it may not start again. Now it won’t even start. I don’t smell gas in the tail pipe or engine so I assume that gas is not getting past the injectors. I have no check engine light codes either. If the computer is bad shouldn’t it throw a code? I’ve looked for an injector relay and can’t find one. I have no idea what is wrong. Perplexed in Arizona. Any suggestions would be appreciated.

Does this truck have the 4-cylinder multi-port injected engine or the V6 throttle body injected motor?

It’s a 4-cylinder 2.6L, should have said that,sorry

Is that a Isuzu Trooper? Is it a diesel? Have you changed the fuel filter?

HelloKit-- it’s a pickup truck, not that it matters since all of the Isuzu trucks of this vintage are pretty much identical mechanically. The 2.6 is a gas engine, though unfortunately not one I’m as familiar with as the 3.1 GM engine also found in these.

To the OP-- Are you sure it’s getting good fuel pressure? Did you actually measure the fuel pressure? Did you change the fuel filter along with the pump? Can you hear the pump running?

There’s a relay for the fuel pump, which should be in the underhood fuse box and there should also be a fuse for the fuel injection in the fuse box under the steering wheel. Give them a check. Depending on how it’s failed, a bad computer usually won’t give a code because it’s what gives out the codes! If you do have a bad computer (or there’s no voltage to the computer) the check engine light won’t come on when you turn the key to run. The computer should be near the bottom of your list, though, because bad computers are very unusual and plus they’re expensive!

Those are sort of the “simple” things you can check before you have to actually measure the fuel pressure and really dig into the thing. The fuel pressure needs to be about 40 PSI with the vacuum line to the fuel pressure regulator disconnected. If it gets any deeper than this, you’ll need a service manual which you probably ought to have anyways.

It’s gas not diesel and I did change the fuel filter when I changed the fuel pump.

I changed the fuel filter when I replaced the pump. I didn’t check the pressure and I didn’t listen for the pump. I did disconnect the gas line from the fuel filter and put it into a gas can. When the gas pedal was pressed it shot out a stream of gas but when not pressing on the gas pedal it’s a slow dribble (constant though). I wasn’t aware of the fuse under the steering wheel will check that in the morning. But I would suspect that a fuse would mean it would stop running, where as this has become a progressively worse condition over time. Not sure what the symptoms of a bad fuel relay are. The check engine light does come on when I try to start the car. Also it does give me the code 12 when in diagnostic mode but nothing else. I don’t think anything is getting past the injectors though. I looked at this one auto manual site and they had a diagram of a fuel injector resistor but then went on to give no details about it other than the cost of the part. Thanks for your advice.

Is there a fuel pressure regulator on this engine. I have a 1994 Rodeo and had the same problem. Ended up being the FPR which hardly ever goes bad. Runs like a swiss watch again.

In addition to checking out the pressure regulator, it is a good time to find out if the injectors have power. You can do a quick, simple check with noid light.

Isuzu is a bit unusual. Its fuel pump has TWO power sources! One power source (12 volts) comes from fuse #11 and goes, fairly straight, to the fuel pump. It supplies power to the fuel pump only when the ignition switch is in START.
The other fuel pump power source (12 volts), goes through the fuel pump relay when the ignition switch is in either RUN, or START.
Here’s the wiring diagram: Click on Fig.40

Just to let everyone know, it ended up being the ECM Relay. Once I got the electrical schematic, it was a piece of cake, because I was certain the fuel injectors weren’t opening. I want to thank all of you guys you were a big help and thank you hellokit for the link to the schematic.