Pedal Pump to Start?

I have to pump the gas a few times to start my car in the morning or after sitting awhile. Also, if I leave it idling it will stumble every once in awhile. Tach will drop and rise. Fuel pressure, gas cap or fuel pump? I've tried to search for vacuum leaks but have not smoke tested. Haven't been able to hook up the Durametric to data log anything due to a failed battery on my laptop. Other than that she runs like a champ!

Similar thing was occurring in my BMW, ended up being fouled spark plugs. Swapped out the plugs and coils and symptom went away. Might be worth it to pop one out and make sure plugs aren't fouled. Durametric might point you in an actual direction rather than my out of the hat guess however.

Strange. I mean, in the old days, pumping the gas worked on carbureted engines because there was a piston that actually pumped fuel into the intake manifold to get the engine started. On these cars, pumping before starting probably does nothing. Pumping usurping starting probably introduces air and fuel that bypasses the idle control mechanism. I agree that fouled plugs could be the cause, as introducing a lot more air without atomized fuel could help clear the cylinders. But I also wonder if the idle control or starting fuel algorithm could also be faulty. I guess I don�t know how the starting procedure on these cars works in terms of idle control versus some other mechanism.

Since its injected and doesn't have an accelerator pump like a carbureted engine, I'm assuming you're referring to giving it gas while cranking it over, rather than to prime it prior to cranking it. On my 99' C2 I give it zero extra fuel with the pedal, and it always fires right off and idles. I'd also be extra careful to avoid revving it at all above idle speed upon start-up because of lack of oil pressure/circulation and operating temperature. Do you suspect a vacuum leak? If you loosen the oil filler cap to intentionally create a vacuum leak when it's idling, does the idle change?

Try this from a few years back Rick https://rennlist.com/forums/996-form/812091-random-hard-starting.html

I crank and let oil pressure build then crank again apply a pedal pump or two or three. I never rev it and keep it between 2-3k until temps are up. I do keep it above 3K while driving most of the time. New Bosch plugs with less than 800 miles on them.

I�m currently working through a similar issue with warm starts. Pumping the throttle adds air not fuel to the mix which makes me think I have either a faulty Evap system or leaking injectors. The rich mix is then thinned out by pumping the gas pedal and starts every time. May be related to your isssue or not. Keep us posted either way and I�ll do the same. As as an aside I have no CELs, no problems filling up and no whistling bottle noises that typical accompany a faulty evap purge valve so like I said, I have some digging to do.

Last year on the 02 C2, had hard starting for a few times like yours, ended up quitting 100 miles from home, no CEL and thankful for AAA premium towing, got it home and found fuel pump failure.

I had a problem with long cranking on hot starts, it was the coolant sensor at the back of the engine.

Have you tried turning the key on and off a few times before engaging the starter? I️ dont know if the 996 fuel system imhas a return or not, but the fuel line has to be under pressure and a pressure leak within the system can initially starve the injectors for fuel for a few seconds. Turning the key on and off would cause the pump to run and pressurize the system. Also could be a weak/failing pump.

I agree with others. Pumping shouldn't have any effect on fuel injected car like the 996. Have you tried resetting your e-gas? I've also had this problem and it ended up being a failing fuel pump system.

Funny enough, I ran my 996 out of gas yesterday, and it sputtered and died. But if I depressed the accelerator a bit, it would run just long and well enough to back it into a parking space. So when you say �pump,� I wonder if what you are actually doing is opening and closing the butterfly valve whereby the opening part of the cycle is what�s actually helping the car start. The way to validate my hypothesis would be - next time instead of pumping, try holding the throttle open at 25% of 50% and leave it there to see if it�s has the same affect.

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What other symptoms led you to the sensor? This is interesting. Last week I discovered a small coolant drip. It looked like it was coming from the sensor so I gave it a little snug (maybe a 1/16" turn) but then realized it was the coolant (clamp) hose above it was cocked. Lost my temp gauge and half way home it came back. No issue since. Always warms up to just north of 180*.

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It certainly does. Pressing the throttle pedal to the floor induces a lean condition, so if an issue w/ a 996 that involves fueling that ultimate leads to too much fuel being in the chamber upon start up, flooring it helps. This is a great lead, thanks! Certainly not trying to hijack this thread, perhaps this would sort out the OP and myself, will look into it as I'm a bit stumped at the moment.

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I know our cars are like 20 years old now, but they are still ECU controlled fuel injection and post 2000 have e-gas (i.e. non-mechanical throttle), correct? Therefore, at startup the ECU handles the startup routine of priming the pump and injecting fuel into the combustion chamber. I haven't forgotten the old carburetor cars/trucks that did require pumping of the gas to engage the choke, but I don't see how pumping an accelerator on modern fuel injected cars is going to make a difference in the situation. Just my 2 cents.

Useful thread!

If the engine is flooded, flooring the throttle pedal while cranking clears the cilinders from fuel laden air. The ECU might even stop injecting fuel, when it detects full throttle AND cranking rpm but that I don't know for certain. Echoing some other posters to this thread, pumping the pedal while cranking does nothing beneficial. Probably nothing detrimental either but if you have a hard starting engine that only starts by pumping the throttle pedal a couple of times, something is amiss. If it starts fine, then it will start without a couple of pumps too.

It might be worth cleaning your ICV if you have a cable throttle car. You should purchase a gasket beforehand as the paper one will likely disintegrate upon removal.