[pfco3]

but it wont start unless i spray a little starter fluid into the intake. it didnt do that while it was in my other rig. the other thing is that if i snap the throttle open it dies. its a 93 4.3 vortec w/ 700r4. im thinking its a fuel problem (i have to dig my pressure guage out). i had a spare cpi unit that i swapped in but that didnt help. anybody have some ideas as to what i should look for?

 

[TNToy]

My gut says fuel problem... Since starting fluid won't compensate for missing spark or air, then that immedaitely points to fuel. It's the only thing required for combustion that starting fluid can replace.

It may be an electrical problem with an injector, or it may be the fuel pump.

Oh - sudden idea: The fuel pump is hooked to an ignition switced circut. Make sure it has power with the switch in the START position... many circuits (I.E. the radio) don't recieve power while starting - they only get it in the ON and ACC positions. Make sure your fuel pump isn't hooked to one of those.

Will it RUN without starting fluid - it just wont START without it, or dies it die shortly after you get it running?

 

[mudtruck44]

What fuel pump are you using? Has it been driven yet? I am thinking that it is not getting enough fuel, and if you drove it you would see a bad driveability problem too.

If this is something that you swapped an electirc pump into. I would also guess that you did not tap into the right circuit, and you don't have power at the pump during crank.

 

[biggnome]

Does this engine have the "spider injectors". If so this system has to have a MINIMUM of 54psi to run.

 

[mudtruck44]

He said he swapped CPI units, so yes.

 

[pfco3]

yes i adapted a gm fuel sending unit assembly to fit in the jeep tank. no i havent driven it yet (waiting for driveshafts). i agree that i will have a driveability problem. im also gonna check for power during crank. oh and once i give it the starting fluid it runs off the pump. know what i mean? i kinda figured it was a fuel problem, ill look more into it tomorrow. thanks guys

 

[TNToy]

Yeah... I'm betting the pump is on a circuit which is not powered in the START position then.

Try leaving the key in the On position until you hear the pump stop running because the rail is fully pressurized, instead of sticking the key in and slamming it straight from OFF to START. Then crank the motor over as briefly as possible to get the key back to the ON position the MOMENT the motor is spinning good, so the pump kicks back in. A buddy did this to his rig, execpt the aftermarket *COIL* was in a ciruit like this, so he only had spark in the RUN/ON position, but not while in START. Once we figured it out, repeatedly bumping the motor over for about 2/3 of a second would get it some spark right as the motor spun to a stop, and it caught every time from then on, on the 3rd or fourth bump, until he got home from the trail ride and could re-wire it.

That was right after we stole one of his winches solenoids because the starter solenoid got fried by all the cranking, naturally.

 

[pfco3]

okay so i did a fuel psi check and got 40 lbs at the rail and soon as the relay shut off it dropped like a ton of bricks. i knew the cpi was good so i drop the tank (again ) after a few tests turns out the sending unit was bad. had a pinhole leak in it! okay i have another sending unit around pop that bad boy in, put the tank back up (again ) bingo! runs like a champ.

 

[Dan Dibble]

Good Job!