91 S15 Jimmy starting problems

[tonyjor]

Here's a perplexing one: I have a 1991 S15 Jimmy 4x4 4.3L that I recently put a new fuel pump in(last July, and again today). When I push on the gas pedal it feels different. Not as much force needed to push it in. The only problem is that it's not getting gas. If I spray starting fluid in the carb it fires up for a couple seconds. The fuel pump and filter are both brand new and all my fuses are good so I don't know where to look next. Any help?

[Jeremy airjer W]

Does this have a throttle body with two injectors on top? If you turn the key to the run position can you hear the fuel pump run for a couple of seconds. If you can't hear it than you need to check for power on the grey wire as close to the fuel pump as possible (leaving everything connected and backprobing is ideal). You should see 12 volts with the key on for a couple of seconds then no voltage. The voltage will not return until the vehicle is turned of then on again or if you try to crank. If you have power to the pump then backprobe the ground wire (black)you should not see any voltage. If you see a volt or more you have a bad ground. If both of these check out than I would suspect the pump has failed again. Have somebody crank the engine while you tap on the bottom of the fuel tank with a rubber mallet. If it starts you just confirmed that the fuel pump has indeed gone bad.

If you can hear the pump run and this is a throttle body injected vehicle (I'm not sure what year they switched to central port injection) check to see if you can see gas coming out of the injectors while somebody cranks. If you do not see any gas check the PCM-B fuse. If its popped than check the wiring at the injectors to see if it has rubbed through near where the air cleaner assembly buts up to the throttle body.

So what we need to no;

-Is it throttle body injected (to injectors on top of the throttle body)

-Can you hear the fuel pump run?

-Can you see any fuel coming out of the injectors?

[tonyjor]

I'm pretty sure it's throttle body. My brother says it's a carb but there's two injectors with 2 wires each that usually shoot gas into the "carbs". Where is the PCM-B fuse? All the wiring to the fuel pump looks good, no cracks or broken wires, and the fuel pump is brand new. I exchanged the one I bought in July for a new one because I thought that was the problem. I can't hear the pump run when I turn on the key. I don't have a multi-meter so I can't physically test for voltage in the wires. Would it help to know that this happened while in a car wash? I shut the engine off, the truck got washed, and I couldn't start it after that.

[Jeremy airjer W]

ECM-B fuse is located in the fuse block under the dash on the driver side. If you don't have a volt meter than you're propably out of luck. Try wacking the fuel tank with a rubber mallet while somebody is cranking the engine over. Please make sure its in park and he/she has a foot on the brake pedal. Be prepared for it to start. If it does start than I would feel pretty confident that the fuel pump has failed again.

[john.wells]

You might want to take a look at the fuel pressure regulator as a possible culprit. It is located in the throttle body, and it's purpose is to make sure the injector gets a metered flow of fuel. If the diaphragm is ruptured or leaking, you won't develop the correct amount of pressure to force the fuel through. The problem with the throttle "feel" is a little weird, but you COULD have carbon build up in the throat of the throttle body where the butterfly opens that MIGHT be catching the butterfly and holding it shut or open. Take a look down the throat while working the throttle. Also, see if there is fuel shooting out of the injector while trying to turn it over (you'll need a helper). I hate to see people throw parts needlessly at their vehicles-sometimes it pays to bring it in to a reputable garage who has the tools and knowledge to quickly assess a problem. I don't want to sound preachy, and I don't personally own or work for a shop (I'm a mechanic for MnDOT). I just hate to see hard earned money wasted by any fellow FM'er Good luck, hope you find the root cause.

[Jeremy airjer W]

Never mind I just re-read the original post. I didn't realize you just put a pump in to it. you said you can not hear the pump run when you turn the key on. Make sure this is the case by getting as close to the pump as you can while somebody turns the key on. If you still can not hear it than you more than likely have an electrical issue.

Something just came to mind. Did you just replace the pump or did you replace the pump and the sending unit. It is pretty common for the connecor inside of the sending unit to burn up. You would see power to the pump but there was no power getting to the pump on the other side of the sending unit. Again you would need a volt meter to check this. Or remove the sending unit and inspect the connector on the inside of the sending unit where it plugs into the top. Again having a DVOM (digital volt ohm meter) makes it a lot easier to confirm. you have described the exact symptom for this (it could still be something else). I have been burned by this once and know I check it every time!!

[tonyjor]

I bought a multimeter. It's just a cheapy but it should do what I want it to. I was thinking, if there's power to the fuel gauge from the sending unit, wouldn't or shouldn't that rule out a faulty power supply? I replaced all the wires on the sending unit prior to putting it back in the tank. The only ones not replaced were the ones that are on top of the sending unit. These should be good if I still can read how much gas is in the tank. At least that one is good and that rules out a bad ground. When I used to push on the gas pedal there was a little resistance and now it feels like there's nothing. Kinda like when your car dies while cruising down the road. Maybe I'll end up taking it in as I am stumped...sucks though, could use that repair money for xmas gifts Thanks for all the help! I'll post as to what the problem is after I take it in. I'm going to monkey around with it a bit more before I do that though.

[Jeremy airjer W]

Quote:

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I was thinking, if there's power to the fuel gauge from the sending unit, wouldn't or shouldn't that rule out a faulty power supply?

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No. There are three wires Ones grey, ones pink or green, ones black. The green or pink one is the one that supplies power to the sending unit for the gauge. It should have power to it the entire time the key is in the run position. The grey wire(sometimes tan) is the power to the pump. This should have power to it for a couple of seconds when you intially turn the key on. (note: These two wires are on completely different circuits). It will not have power to it again until either the key is turned off then on again or until you try to crank the engine over.

So it is possible for the gauge to be working just fine and have no power to the pump. you can measure the continuity between the black wire and grey wire to see if the cuircuit that goes to the pump is open. if it is I suspect a bad sending unit (the part that the pump mounts to)

As far as the gas pedal????? Can you see the throttle linkage move when you push down on the pedal?

At this point I would have to agree that maybe it is best to bring it in to a repair facility. It should run about $100 max for the diagnostic time. This should be a farely easy diagnosis for an experienced tech.

[MIKEYMN]

You have one of them problems that could be 20 different things, but you keep you talking about lighter throttle pressure makes me think TPS (trottle position sensor). It has a spring in it and if fails at wide open throttle when trying to start the engine the computer will shut the fuel injectors off. It think you flooded the engine. kinda like when you flooded a carb engine and you hold the throttle to the floor to clean the gas out . Well I hope this helps ,like I said it could be 20 different things. GOOD LUCK!!!!

[Valv]

I just wanted to add if you want to run pump longer than few seconds, try to start engine with key but just tap starter with it, it should run pump for 5 to 10 seconds, then turn key off, repeat procedure.

[Jeremy airjer W]

Good sugestion mike except the butterflies have a pretty heavy spring that counter acts the pressure of the gas pedal. The spring pressure of the TPS is so minimul that you would not notice the lack of pressure if it where to break. However as you mentioned if the TPS is reading/sending a wide open throttle signal the PCM and the PCM will interpret that as a deflood and kill the injectors.

I think a scan tool, Some basic Diagnostic tools, and a little experience will solve this one. Believe me, if you been in this business long enough nothing on a blazer/jimmy will surprise you and you will see or repair everything possible at least 6 six times.

[tonyjor]

You guys are gonna laugh. I got a co-worker to come over after work today so I could have him turn the key while I tested the wires. They both tested good so I connected them back up and asked him to turn the key again so I could listen for the pump. I heard the pump go so I ruled that out. I figured it was something with the injectors. So, I took the air cleaner and such off so I could watch the injectors as I turned the key. Lo and behold, gas comes out. So, now it's an electrical problem ala the coil. I take the coil wire off the distributor cap and off the coil. Then I put it back on and the truck starts It was connected well before I removed it so I don't know what the deal was. Anyways, all the help was greatly appreciated and I thank all of you. Now, with the weather the way it is, it looks like I'll be able to use the truck to pull my gear next weekend

[Macgyver55]

Its possible the coil wire was arcing to ground and by repositioning it, it is not doing it now. If thats the case the wires are probably due for replacing.

[Jeremy airjer W]

No, The original post said it would run for a couple of seconds with the use of starting fluid. I'm sure this problem will show up again. If it was ignition than why would it run with the starting fluid???

[Macgyver55]

Oooops, I didn't follow the thread from the begining and only read his last post. I should know better than to chime in before reading the whole story.

[Jeremy airjer W]

You're forgiven!