Have to pump gas pedal to get it to start, then it runs fine??
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HT4100 4.1, 4.5, 4.9 Discussion, Have to pump gas pedal to get it to start, then it runs fine?? in Cadillac Engine Technical Discussion; I took my car a 1993 SDV, to a trusted mech. (mistake one), becuase my FDC was going in and ...
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    Question Have to pump gas pedal to get it to start, then it runs fine??

    I took my car a 1993 SDV, to a trusted mech. (mistake one), becuase my FDC was going in and out and somtimes displaying a "C" only, with code F31, in addition to the car not wanting to start unless you pumped the gas pedal atleast three times, before turning the key (only happens when cold, or sitting for awhile). He said he knew for a fact (mistake two) that it was the fuel sending unit, so I bought an AC delco fuel pump, sending unit and a strainer. An ass load of money later, the car is doing the exact same things, now ass money, is trying to tell me it's the BCM, I'd like this not to be mistake three. The plugs, wires, cap, rotor and coil where replaced about 40K ago, the battery could be replaced though, when pumped or warm the car fires right up, any ideas would be appreicated, thanks.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Try a bottle of Lucas fuel treatment


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    awadecki is offline Cadillac Owners Enthusiast
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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Pumping does nothing on fuel injected cars before you turn the key on. There's no fuel system pressure, and the injectors will not turn on unless the key is turned to "Start." It's not like a carbureted car where the accelerator pump would squirt gas into the venture when you pumped it. So, not quite sure what your problem is.

    My only guess might be your EGR valve is sticking open, and that the pumping action creates enough vibration to unstick the diaphram. Push up on the underside of the EGR. If it is sticking, replace it. Next time, before you crank the car, tap the EGR a few times with a wrench. Then, without pumping, try to start it. If it starts, the tapping temporarily unstuck the diaphram and allowed the car to start.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    I thought I read somewhere in this forum that depressing the gas pedal dumped fuel into the injectors, something about computer going onto dump mode? So not a chance it could be the BCM or Fuel pres reg.? EGR has about 20K on it, but I'll check to see if it went bad.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Checked the EGR, goes up with one finger, without sticking. Squeaks alot, but moves.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    squeaking is OK. pushing the gas pedal to the floor puts the computer into "clear/flood mode" where the injectors will not pulse. it's used when the vehicle is flooded--not to squirt extra gas.

    if the fpr was going bad you'd have a problem with hot starts, not cold starts. best bet is to buy a fuel pressure gauge and check the fuel pressure. the only thing you do by pumping the pedal with the key off is opening and closing the throttle blades.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Thank you for the reply, what should I be looking for?

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Well, before you buy the fuel gauge, are you sure that the fuel filter was replaced with the pump? If not, this may be causing low line pressure when you first crank it. Another thing to look for before buying a fuel pressure gauge...

    When you first turn the key to the "On" position, listen for the fuel pump to kick on for 2 seconds before you attempt to start the vehicle. If it doesn't kick on, the fuel system won't prime until the oil pressure switch closes (after about 5 seconds of cranking). Check to see if you hear this. If not, replace the fuel pump relay. It's only $8 or so, and commonly goes out on these GM vehicles.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    The fuel filter was replaced about two weeks before the pump and sending unit were. Weird thing though, usually the fuel will pour out of the filter, not too much though. This time, the fuel sprayed out, like it was coming out of a high pressure hose, quite a bit too. I can hear the pump engage before I turn the key. Could it be the BCM? Becuase it's more than just no fuel at start, it's an inter. FDC dispaly, that is either blank, working or showing a "C", in addition to a F31 (map sensor code). When this code first showed I replaced the MAP sensor, but to no avail, the code still returned. Thanks for keeping up this post I appericate it.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Your BCM may be bad, but usually the ECM is what controls the engine and starting (there are 2 computers in your car). The BCM controls the FDC and climate control, A/C, heat, etc. while the ECM interfaces with it, but pretty much runs its own code.

    The fuel pressure should be around 40 psi, so it's reasonable that a lot of fuel came out. One thing that may be happening is that your fuel pressure diaphram is sticking, but not leaking. It might be the case that it's not permitting enough fuel to go back to the tank, or making the pump work extra hard to get it back into the return line. I haven't seen this on a PFI 4.x car, but this sometimes occurs on the throttle body models. Take the vacuum hose off of the pressure regulator and squirt a lot of WD-40 in there. Then, put it pack on and blip the throttle about 15 times. Shut the car off and do it again. See if you notice any difference in starting the next day.

    The code for the MAP is an ECM code (not BCM). This could be your problem. What kind of code are you getting (MAP too high/MAP too low)? If the ECM can't read the MAP properly, the vehicle will have a hard time starting. You can try cold starting the vehicle with the MAP disconnected to see if that will make any difference. It will run horribly, but it will start. Check your MAP vacuum hose at the throttle body and also at the sensor. Buy an identically-sized vacuum hose from an auto parts store and put it on (keep the old hose just in case).

    One last thing: you may have a bad ISC. More specifically, a closed throttle switch, or sticking motor. Pumping your car and repeatedly i.e. letting the throttle come to a rest on the ISC plunger may jar a bad/stuck motor loose, permitting the vehicle to start. Here's a way to check this: try cold starting your vehicle with your foot slightly depressed on the accelerator pedal (about 1/4 of the way down). If your vehicle starts instantly, your ISC motor is not stepping out on a cold start, so basically, you don't have enough throttle to get the vehicle going. My guess is that the pumping action jars the stuck ISC motor loose, permitting it to advance to its proper position before cold starting. This could also be the source of your MAP code error. If the throttle isn't advanced enough for a cold start, it will cause a MAP sensor error because the MAP vacuum reading won't correspond to what the computer is commanding for a given throttle opening. Diagnose/eliminate this issue first, BEFORE proceeding to the other things I've mentioned in this post.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    WOW... thank you so much for the info, I'll start the list in the morning and see what happens.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    I'm assuming the ISC motor is the one with the silver armature that pushes against the throttle. Come to think of it, that little arm would always make little adjustments, that I could hear when I turned the motor off. I just went out to the car and tapped the throttle to the ISC and it started fine, I also had a friend start the car and turn it off while I watched, that armature didn't move or make sound one. So can I assume the ISC is bad?

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Yes, it's the black motor with a little metal plunger that moves the throttle. It's highly likely that it's bad. They tend to last around 60k miles or so. Generally, the ISC will cycle back and forth 3 times after you shut the key off. If it doesn't, or doesn't move when you start and shut off the vehicle, then there's probably an issue with it.

    Start by troubleshooting the ISC motor.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    Thank you for the info, my ISC has 154K on it. I'll drop a new one in the car and see what happens.

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    Re: Have to pump gas pedal to get it to start, then it runs fine??

    It indeed was the ISC motor, quick and easy fix, thank you for your help.

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