Do you need to do any adjustment in engine after replacing fuel pump?

[francesconyc]

I'm trying to isolate different problem i have when starting the car.

I replaced my old noisy/whining fuel pump two days ago.
it did work great the same afternoon. good acceleration, idle at 1,000 rpm all day when in traffic, tested on all gears, and no hesitation whatsoever.

but then the next day I had this issue of rough idle when starting the car. So rough sometimes that it dies after touching the gas pedal (air bubble in the fuel lines??).
Never had this before. Actually, I used to have the opposite of the car going to 2,000 rpm back and forth until it reached a stable rpm.

so my first thought was the culprit must be the fuel pump. maybe the hoses/clamps? electric wires connectors?

so my questions are:

• is it possible the pump went bad after one day?
• is the pump a pure plug-and-play element?
• Is it possible that a bad fuel pump is bad only at the start, but great after waiting and running?
• Does the CIs/jetronic, or what not, need be readjusted for the new pump?

thanks!

NOTE: battery is almost new, alternator rebuilt. starter, maybe old stock but starts.

[PeteKz]

The pump is a plug and play replacement. No CIS adjustments necessary.

An early pump failure is unlikely, but possible, especially if it's made in China. I haven't seen a pump be bad at the start and then get better, or warm up.

[Bill Douglas]

Pete, while we have you here... What are your thoughts. I replaced my fuel pump on my ROW SC with the correct one for the car (can't remember the model) and the car ran very well like it always does. The old fuel pump was actually a BMW model according to the place that sold me the new one. Now the car seems to be chewing through the gas a bit too quickly. I've got no idea of actual miles per gallon, but it used to be very fuel efficient and not so much now. Umm, any ideas - thanks.

[Schulisco]

Originally Posted by Bill Douglas

Pete, while we have you here... What are your thoughts. I replaced my fuel pump on my ROW SC with the correct one for the car (can't remember the model) and the car ran very well like it always does. The old fuel pump was actually a BMW model according to the place that sold me the new one. Now the car seems to be chewing through the gas a bit too quickly. I've got no idea of actual miles per gallon, but it used to be very fuel efficient and not so much now. Umm, any ideas - thanks.

Compare the tech specs between both pumps. The fuel efficiency on a CIS is always related to the mixture buildup. This means the CIS requires as much as pressure as it is designed to have. The better the pressures, the better the mixture build up. The BMW pump may generate higher pressures but they got controlled by the fuel pressure regulator. As said, in general is a fuel pump replacement a plug'n'play job. But IMO it is always a good idea to check the control and system pressure on a CIS afterwards the replacement just to be sure that they're in spec. If the old pump didn't pressurized the CIS as the new does, and the CIS has been adjusted to the old pump, then IMO it's necessary to readjust the mixture as well, because this affects also the fuel economy and the performance.

https://forums.pelicanparts.com/porsche-911-technical-forum/1159036-occasionally-slow-start-after-city-drive-3.html#post12232751

Thomas

[Dpmulvan]

Originally Posted by francesconyc

I'm trying to isolate different problem i have when starting the car.

I replaced my old noisy/whining fuel pump two days ago.
it did work great the same afternoon. good acceleration, idle at 1,000 rpm all day when in traffic, tested on all gears, and no hesitation whatsoever.

but then the next day I had this issue of rough idle when starting the car. So rough sometimes that it dies after touching the gas pedal (air bubble in the fuel lines??).
Never had this before. Actually, I used to have the opposite of the car going to 2,000 rpm back and forth until it reached a stable rpm.

so my first thought was the culprit must be the fuel pump. maybe the hoses/clamps? electric wires connectors?

so my questions are:

• is it possible the pump went bad after one day?
• is the pump a pure plug-and-play element?
• Is it possible that a bad fuel pump is bad only at the start, but great after waiting and running?
• Does the CIs/jetronic, or what not, need be readjusted for the new pump?

thanks!

NOTE: battery is almost new, alternator rebuilt. starter, maybe old stock but starts.

What brand pump is it? Is your tank and fuel filter clean?

[David Inc.]

So you just have the issue during startup, and it clears out when everything's warm? The previous issue with idle surging wasn't good either. Sure everything else is healthy? Good mix? No vacuum leaks?

[francesconyc]

yes, it happens ONLY at startup and ONLY when hot.

yesterday for instance I started the car and it was all good. (4-5 cranks and good RPM right away, no hesitation, no shaking, no sputtering)

it seems that the issue is only when the car is really hot (oil temp slightly above the second white mark but not in red of course). this happens when I drive in the city (I'm in NY) and if I drive for an hour of stop-and-go at 25mph it gets hot fast. this is when the hot start problem happens.

I think replacing the filter/pump/accumulator has just made it worse because MAYBE the PO setup the engine/warm/cold valves as a bandaid.

i definitely need to check for vacuums etc. but when the car starts cold it drives flawlessly and great acceleration when I press gas.

[francesconyc]

Originally Posted by Dpmulvan

What brand pump is it? Is your tank and fuel filter clean?

The tank filter was replaced the same day. fuel filter and new accumulator 1 week old.

I think the pump is URO or Danks. but that is a pointless factor, to be honest, considering is only a day old, if it was faulty I would have discovered right away.

[David Inc.]

Hot start issues are common, I'd suggest doing a search on them you'll probably find others who dealt with the same problem. Not a fuel pump problem.

[Bill Douglas]

Thanks Thomas. That makes sense. Much appreciated.

[boyt911sc]

Without knowing your fuel pressures (CCP, WCP, SP, & RP) you are just working blind and guessing. Do you have access to a set of pressure gauge? If it takes multiple attempts to get your motor to start every time you drive your car, something is wrong with your CIS. And the problem will not go away. You need to test and identify the culprit/s.

Tony

[kltarga72]

Originally Posted by francesconyc

yes, it happens ONLY at startup and ONLY when hot.

yesterday for instance I started the car and it was all good. (4-5 cranks and good RPM right away, no hesitation, no shaking, no sputtering)

it seems that the issue is only when the car is really hot (oil temp slightly above the second white mark but not in red of course). this happens when I drive in the city (I'm in NY) and if I drive for an hour of stop-and-go at 25mph it gets hot fast. this is when the hot start problem happens.

I think replacing the filter/pump/accumulator has just made it worse because MAYBE the PO setup the engine/warm/cold valves as a bandaid.

i definitely need to check for vacuums etc. but when the car starts cold it drives flawlessly and great acceleration when I press gas.

This is what I experienced a couple years back after I purchased a Bosch fuel pump. It worked good for a month and then I experienced the same issues you describe. Mechanic replaced the fuel pump and all problems disappeared.
The first pump was made in Mexico or south America.

[PeteKz]

Bill, I think Thomas covered your questions, so let me add a bit more.

IF the pump meets the delivery test, then functionally it does not matter what pump you install. If it passes the delivery test, then it delivers sufficient pressure and volume to the CIS.

It is still a good idea to check the pressures when you replace a CIS component, as Thomas suggested, just in case you whacked or pulled wires while you were in there.

[Bill Douglas]

Will do, thanks Pete.

[Alan L]

Bill, if you ever wanted to venture as far north as Hawkes Bay I would be prepared to check your system over.
Alan

[Bill Douglas]

Thanks Alan. I have relatives in Poukawa I have been promising to visit for years. So I may take you up on the offer. Plus 6,000rpm in top gear along the Takapau is always fun.

[Alan L]

PM me if/when you have a plan. I am off o/seas end of May for a bit.
Regards
Alan

[Bill Douglas]

Will do - thanks.