jb55555

ok i need some help. i have a 89 s5 rx7. i bought the car from a junk yard cheep and rebuilt the engine. after completed the heater core went and had to bypass. had a huge intake leak that i just fixed 2 weeks ago. i was driving on the highway a week ago and i started getting hessitations. the hessitations only happen when its above 3800 rpm and im increasing speed. it happens at all speeds any gear and at random rpms. i researched thew infomous 3800 rpm hesitation. i cleaned all the grounds, checked and adjusted tps with check light, changed the fuel filter, and checked the Exaust system. Now the car was sitting in the yard for a year so when i got it i put stabalizer in it fiqured it was all bad. so yeassterday i started to check the fuel system and this is what i got.
Fuel pressure 12psi
Fuel pump max pressure 45psi
And i get allmost no pressure when the car is running
I think i have a bad fuel pump but the instructions i have are vage. what do you think any segestions?

jb55555

btw, the sensor on the rearhousing for the coolant temp gauge is broken and when i hold the gas above 4000 rpms for 5 seconds it sounds like its missing

jb55555

anybody?

WAYNE88N/A

Have you checked your inlet filter on your fuel pump yet?

jb55555

how do you check that?

WAYNE88N/A

Pull the pump- do you have a Haynes manual, or the FSM?

jb55555

ok just pulled the pump and the filter lookes good. maybe a pressure reg?

WAYNE88N/A

Could be...At this point you're down to 3 items that could cause this- bad wiring to the pump, bad pump, or bad FPR. Make damn sure that filter is good-even when they're clogged, they don't look clogged. If you want to make sure, just pull the sock off of the pump, reinstall the pump, and see if anything changes. This is just for temporary troubleshooting, of course, as you don't want any debris from the tank ruining your pump...

jb55555

so your saying i should take the filter off and install and check me pressuer again? what should my pressue be when im running at idle?

jb55555

is the s4 fuel pump the same as an s5

WAYNE88N/A

Dunno, but your pressures at idle should be around 30 psi, I think...

jb55555

where is the fpr located at?

jb55555

ok i just replaced the fuel pump and im getting the same reading. i want to replace the fpr but i cant find where it is located at. anybody know. how does the fpr regulate fuel pressure. what sensors are involed

WAYNE88N/A

The FPR is nothing more than aspring-loaded relief valve, with an extra sensing port at the "back" of the spring chamber that uses vac input pressures to keep the relief values constant relative to manifold pressures (that make any sense, lol)...On an S4, it is located at the forward upper fuel rail (secondary rail), held on by a couple of bolts (10mm, IIRC), and sealed to the rail by an o-ring...

Another little "troubleshooting" step you can do is remove the vac source from the FPR, your fuel pressures should increase about 8-10 psi, if everything is working properly...

WAYNE88N/A

You should also be checking your input voltage at the fuel pump connector, while you're back there...Since I don't know what car you have, you can look up the pin/wiring colors in the FSM wiring manual...

jb55555

i have the same fuel pump as you. i swaped with an s4 and it does match up. which wires do i check?

jb55555

ok i checked the blue and black wires for voltage with the key in position 2 and i got a womping 12v. has any one ever run a sepperate power supply??

WAYNE88N/A

A 'womping' 12v is good