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Thread: 01 4.3 won't start...fuel issue I believe, need some help!

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    Question 01 4.3 won't start...fuel issue I believe, need some help!

    As a brief introduction, I have a 91 Jeep Wrangler with a 4.3 from a 2000 Blazer. This swap was done about 9 years ago and has been great for the most part. Within the last year, I would have a problem starting the Jeep if it had sat for several days to a week without running. At that point, I could crank it until the batter died and not get it to start. However, after an hour or so of sitting (and recharging the battery), it would fire up just fine (and continue to start easily as long as it didn't sit for an extended period of time again). That problem eventually progressed to where it is now, which is that I can't get it start at all. I have fuel to the schrader valve and good pressure as well (it's been a week or so since I checked it, but I believe it was around 35-40 psi). I also have spark. With starter fluid in the tb, the engine will run briefly, so I believe my problem to be somewhere within the fuel injection system. I installed a new fuel pressure regulator and that didn't change anything. What I'm wondering is if the "spider" as I've seen it called, possibly needs to be replaced, as well as if there is anything I can do to test it or each individual injector. I know on my 89 Chevy with TPI, I can ohm check each injector, but I am not familiar with working on this CPI system. Any assistance or advice anyone can offer would be greatly appreciated.

    Thanks in advance,
    Derek

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    As a follow up question, what is the difference in the injector assemblies that are listed as SCPI replacements (part number 833221026 on rockauto.com) and the ones that are listed as SCPI to MFI conversions? Is the latter an upgrade and if so, does it install just like the original, or does it require other modifications to be made?

    Thanks again!

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    Zombie Killer 6SpeedBlazer's Avatar
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    your fuel pressure is to low. it needs to be closer to 50-60psi. i don't have my books in front of me so i cant give you a more exact number. i know the vortec 5.7 in my 89 blazer idles at about 55psi.

    the stock injectors on the 4.3's from 96-02.5 used an injector in the metering body with a poppet nozzle at the tip.

    the MFI conversion is new version. there is no injector in the metering body and it houses a pico injector in the tip of the nozzle.

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    The fuel pressure you stated is way low. It needs to be between 54-62. Last time I checked mine it hovered around 58 at idle. The poppet valves need higher pressure to opporate correctly. Since you said you changed the regulator it could be a poppet is leaking or a bad injector.

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    Upright Member smsmith36's Avatar
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    I had the same thing happen when my nut kit was bad. One of the lines had a little pin hole in it and when you shut it off, it would lose pressure and not want to start.
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    Zombie Killer 6SpeedBlazer's Avatar
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    Quote Originally Posted by mrleprichaun View Post
    The fuel pressure you stated is way low. It needs to be between 54-62. Last time I checked mine it hovered around 58 at idle. The poppet valves need higher pressure to opporate correctly. Since you said you changed the regulator it could be a poppet is leaking or a bad injector.
    most likely the fuel pump is dying. or it has an intermittant loss of connection that could be caused by the wires inside the tank at the sending unit getting hot and melting, a melted connection at the top of the sending unit, or a corroded ground wire.


    Quote Originally Posted by smsmith36 View Post
    I had the same thing happen when my nut kit was bad. One of the lines had a little pin hole in it and when you shut it off, it would lose pressure and not want to start.
    96+ motors do not have nut kits.
    Last edited by 6SpeedBlazer; 05-11-2010 at 07:25 PM.

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    Yes it could definately be an electrical issue and /or pump going bad as well.

    Does the pump prime when you turn the key?

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    Since my pressure is so much lower than what is required for the injectors to work, I'm leaning towards the pump failing as well. The pump does prime when the key is on. Also, I am running an external pump and an Autometer sending unit in the stock Jeep tank.

    Sorry for the delayed answers today, I put the Jeep on the trailer and hauled it into to town to pull codes and possibly drop off at my mechanic. We discussed for awhile and he said the first thing I should concentrate on was getting the pressure up to where it should be. He also happened to have a 4.3L Astro Van in the shop that he was replacing the fuel pump in because it was not putting up enough initial pressure to get it started. I think my first step is to pull that pump and bench test it separate from the lines on the Jeep to see if it is actually putting out enough pressure. Right now I'm sifting through Summit to try to find a suitable replacement, if need be. Does anyone know what volume I should be looking for? I know the pressure needs to be between 54-64 psi to start it, but I haven't seen any volume requirements. My mechanic also said I should be using no rubber lines on a high pressure system like this, and no smaller than 3/8" steel line.

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    Zombie Killer 6SpeedBlazer's Avatar
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    Quote Originally Posted by shiner2001 View Post
    Since my pressure is so much lower than what is required for the injectors to work, I'm leaning towards the pump failing as well. The pump does prime when the key is on. Also, I am running an external pump and an Autometer sending unit in the stock Jeep tank.

    Sorry for the delayed answers today, I put the Jeep on the trailer and hauled it into to town to pull codes and possibly drop off at my mechanic. We discussed for awhile and he said the first thing I should concentrate on was getting the pressure up to where it should be. He also happened to have a 4.3L Astro Van in the shop that he was replacing the fuel pump in because it was not putting up enough initial pressure to get it started. I think my first step is to pull that pump and bench test it separate from the lines on the Jeep to see if it is actually putting out enough pressure. Right now I'm sifting through Summit to try to find a suitable replacement, if need be. Does anyone know what volume I should be looking for? I know the pressure needs to be between 54-64 psi to start it, but I haven't seen any volume requirements. My mechanic also said I should be using no rubber lines on a high pressure system like this, and no smaller than 3/8" steel line.
    what motor did the jeep have from the factory? what fuel tank did it come with, and whats in it now?

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    I believe the stock pumps are rated at about 65ish gph.

    http://www.summitracing.com/parts/CRT-P5000/

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    Quote Originally Posted by 6SpeedBlazer View Post
    what motor did the jeep have from the factory? what fuel tank did it come with, and whats in it now?
    The Jeep originally had a 2.5L fuel injected 4 cylinder (two of them, actually) and the stock tank is still in the Jeep. I made an adapter to allow the Autometer sending unit to fit the original sending unit/pump hole on top of the tank and made my own in-tank pick up and sock out of hard line that runs to the bottom of the tank, much like the stock set up.

    I've been out trouble shooting some more and these are my findings. I disconnected the fuel line in front of the inline filter 0located directly in front of the tank on the driver side frame rail) and pressure tested there. That gave me 65 psi. Aware that my battery may not be at full charge, I hooked the Jeep up to a Cummins via jumper cables and then checked the pressure in front of the inline filter (located about a foot in front of the pump on the driver side frame rail) and got a reading of 75 psi (I assume the reading in front of the pump would have been nearly identical if the Dodge was running it when I checked it. I attribute the 10 psi difference to the battery). I then went back to the schrader valve at the intake and was getting about 48 psi there. Obviously, I was still unable to start the engine. Also, I have recently replaced the fuel pressure regulator, which I believe may still be at fault. I filled the line with fuel (clear inline fuel filter) and pulled the line from behind the filter, leaving a column of fluid from the engine to the filter. With an air compressor set at only 30 psi, I emptied that column of fluid easily from filter to the engine, pushing it through the return line and back to the tank. This leads me to believe that the fuel pressure regulator is dumping fluid and not allowing the system to build the appropriate pressure needed to start the engine. Also, by squirting small amounts of gas into the throttle body, I can get the engine to run, but not stay running once I stop manual introducing gas into the equation.

    This leads me to believe that A) my fuel pump may be on the decline as its only putting out 75 psi, but it's rated at 125 max psi, and B) I have a bad fuel pressure regulator that's not allowing the system to reach the necessary pressure.

    So, that's where I stand now. Tomorrow I think I'll go swap out the regulator for a new one and see if that helps at all. If not, I'll probably order a new pump.

    Many thanks for all the help, I look forward to everyone's response!

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    Quote Originally Posted by 6SpeedBlazer View Post

    the stock injectors on the 4.3's from 96-02.5 used an injector in the metering body with a poppet nozzle at the tip.

    the MFI conversion is new version. there is no injector in the metering body and it houses a pico injector in the tip of the nozzle.
    When going with the newer version of the injector, are the pressure requirements the same (54-64psi)? Also, are there any other modifications or changes that need to be made or is it just as easy as replacing the old spider with the new one? How about performance/reliability gains...anything?

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    Upright Member smsmith36's Avatar
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    Quote Originally Posted by 6SpeedBlazer View Post

    96+ motors do not have nut kits.


    My bad. I didn't pay attention to the year. Symptoms sounded the same as I had.
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    Quote Originally Posted by shiner2001 View Post
    When going with the newer version of the injector, are the pressure requirements the same (54-64psi)? Also, are there any other modifications or changes that need to be made or is it just as easy as replacing the old spider with the new one? How about performance/reliability gains...anything?
    the pressure requirements are still the same, but the MFI injectors arent as bitchy when it comes to fuel pressure when compared to the old poppet style. the poppets can fail with the psi at the bottom of the spec listed.

    the mfi injectors are NOT a performance upgrade, they can make the vehicel run better if the old injectors are bad though.

    get a jeep fuel pump from a 94ish jeep with a mpfi 2.5 and install it in the tank. get rid of the frame mounted pump.
    Last edited by 6SpeedBlazer; 05-12-2010 at 01:27 PM.

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    Quote Originally Posted by 6SpeedBlazer View Post
    the pressure requirements are still the same, but the MFI injectors arent as bitchy when it comes to fuel pressure when compared to the old poppet style. the poppets can fail with the psi at the bottom of the spec listed.

    the mfi injectors are NOT a performance upgrade, they can make the vehicel run better if the old injectors are bad though.

    get a jeep fuel pump from a 94ish jeep with a mpfi 2.5 and install it in the tank. get rid of the frame mounted pump.
    The in tank pump for the Jeep only puts up 31 psi with the vacuum line attached at the factory Jeep pressure regulator and 39 with it disconnected. This wouldn't satisfy the requirements of the 4.3 for pressure, correct? Right now I am getting 48 at the schrader when running just the pump in the "on" position when jumper cables are attached to another running vehicle and can't get it to start.

    I am just about to go test with an elevated, external, gravity feed fuel tank connected to the current frame mounted fuel pump and see if my pump/tank orientation might be causing some issues. What gets me about this whole setup is that it ran great for years as it is now. I am wondering if the fuel pump has finally just declined to the point that it can't keep up.

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