Fuel pump or filter issue ?

[morris400]

Car is a 94 s4, in the morning or after it sits for even just a hour it takes forever to start. I will turn the key and it will crank but not fire up, then I turn key to acc, then try again and 99% of the time she will start right away.

If I park the car on a down hill slope (hood down trunk up) she will 90% of the time just fire up first key turn but if I park on flat ground or up hill slope then I have the above problem.

What do you guys think it can be? Pump filter ect ?

Thanks guys

[Toph]

You're looking in the right direction, I'd say...

A filter change is pretty easy on early audi's (not sure about c4 specifically), and if it were gunk'd up it would inhibit flow, taking the fuel longer to reach the injectors. Did the car sit for any period of time? When was the filter last replaced? You do hear the pump every time you crank, right?

[UrSobsessed]

Start by changing the filter. It's super easy, and if you don't know when it was last done, it's a good idea. The pumps on these cars can go out pretty much without warning anytime after 120-150k. Motronic doesn't prime the system since there is a check valve in the pump. The pump is kicked on when the ECU determines the crank and cams are lined up. Does it make a difference if the tank is full or not? How does the car run once on?

[morris400]

Does not matter if full or low, still takes forever to start . Once running she runs like a dream, no issues. I did get a 2121 code but I'm not sure that would have to do with the pump. I'm gonna clean out my ISV and see if that rids the code.

[morris400]

Bumping this just to see what you all think? I have not got around to the fuel filter of yet but hope to this weekend. Would the car throw a code for cam sensor?

[pilihp2]

If it was the fuel filter I believe you'd see issues while running and at boost. But it's never a bad idea to change it out

[ur20v]

Any noticeable smoke when it does finally fire? Maybe the injectors are leaking down...

[morris400]

No issues what so ever once it's started, In fact I even took the car on a 1200km road trip last weekend and she ran perfect...just takes a long time to start.

[ur20v]

G28 engine speed sensor is probably going bad. Its the one with the grey connector, lower of the two.

[morris400]

I'll check the g28 sensor today, I read that there magnetic so I'll see if its dirty and clean it. Thanks for the help guys.

[ur20v]

Yep, they're just VR sensors. Hopefully you'll find chips and filings stuck to the end of it, but keep in mind erratic behavior that can be correlated with difference in temperature is a symptom of failure... 20 year old electrical parts :(

[morris400]

The sensors were clean, a bit of carbon on them but nothing stuck to them. I'm leaning towards cps now but why does the car start better ifs facing downhill aposed to up hill? This has me baffled.

[PRY4SNO]

Backsiphonage of the fuel. There likely is not a check valve downstream of the filter/pump and it's draining back to the tank when static FP goes down with temperature.

I'm having the same issue as you but I'm leaning towards small holes due to corrosion at the clamps that hold the fuel lines to the underside of the body.

[morris400]

maybe when your back intown i should come over and we can take a look at both cars and see. wqhen it come to the fuel system im lost in the dark. and again this morning the car started fine after sitting all weekend facing downhill.

[PRY4SNO]

Yeah ill trade you fuel system for an oil leak lol

[morris400]

i fixed my oil leak....so no lol

[ur20v]

Is the filter under the hood just north of the airbox like in the S6?

[morris400]

Yes it's under the hood, I'm just worried that if I changed the filter, it won't start again lol. The DIY says you need to start the car then pull the fuel pump fuse till the car stops to release the pressure in the fuel lines then swap filter.

[PRY4SNO]

You'd just have to crank a bit to build pressure. NBD man.

[ur20v]

Or even better, don't park it downhill one night and change the fuel filter the next morning without starting it. See if there's any residual pressure between the filter and the fuel rail.

[Toph]

Wicked smart...get two birds stoned at once!

[morris400]

Well I changed the fuel filter today, when I pulled the FP fuse the car died right away, swapped the filter and the car started after a few cranks, then resized I installed the washer on the wrong side of the banjo bolt. So I pulled the fuse again to fix this problem and this time with the new filter it took almost a min for the car to stop running. Is this a good sign?

I also changed the oil and got rid of the k&n air filter and replaced with a Mann.

[morris400]

ok so this morning the car was facing dwn hill and started fine. drove to work (50k) and parked. car sat for a hour and a half and when i went to start it it took forever again. im guessing im looking at clogged fuel lines maybe?

[morris400]

Another update, I swapped tps sensors and no change, took a look at the FP relay and found this, could this be a bad relay or is this normal?

[ur20v]

Looks normal to me. You'll always see some discoloration on relay terminals, especially older high-quality relays that used real silver.