hello all

i have a 1990 4x4 saph and have been having intermitent hesatation problems which i think are electrical . i traced a problem to the rev counter when i unpluged it the car ran fine got the new part fitted it but the prob is still there then we decided to check the voltage at the fuel pump and the coil the voltage at the fuel pump drops to 9.5 when the fan comes on or when the power is drained by lights and stereo with 4 ways on so should we rewire the fuel pump in case the wire has gone bad or what else could it be the battry is fine so is the coil

what you think

 

Sounds like you do need to rewire the fuel pump.

Also check the ECU voltage (needs a good supply).

May be worth inspecting/replacing the fuseable links at the battery that supply the fusebox (unwrap 8 inches or so of the wiring that connects to the +ve battery terminal until you find the joints and you'll probably find they're corroded).

 

cheers jon

going to re-wire fuel pump ( bosch 044 ) which gauge of wire and relay should i use when doing this and what voltage should i get when the Engine is under load i.e fans on when on boost

the Engine is stage 3 with a T3/4, -34, 500 intercooler, ported head , greens E A chip and I have a digital boost controller Greedy pro spec II etc............................................... ....................................


will

 

Get the wire so it's thick enough to carry the current and not cause a voltage drop - if you get wire rated at 30A, then this should be up to the job.

Run the new wire directly from the battery (with a new 30A fuse near the battery) to pin 30 of a new 30A relay in the boot area. Run the same size wire from pin 87 of the new relay to the pump +ve terminal. Run the same size wire from the pump -ve terminal to a good earth. Use the current wiring that runs to the pump +ve terminal as the switching wire on the new relay (pin 85)(using the original wiring to switch the new relay means that you are still utilising the ECU to switch off the fuel pump in the event of an "incident" and also the kill switch in the spare wheel well). Finally, run a smallish wire from relay pin 86 to earth.

After rewiring, you should get well over 12V at the pump at idle.

Don't forget to have a look at the fuseable links at the battery - corrosion of these is a common problem.

 

thanks jon

should be doing it at the weekend so it`s fingers crossed

 

THey don't use anything like 30 amp so 28/030 is ample!!
This carries 17.5 amps continuous, which is way more than it will ever consume, my own car uses this gauge of wire.
My car consumes a max of 9 amps peak when measured.
tabetha

 

I've been recommended to use 10mm diameter wire (that'll carry about 70A) for my application to ensure minimal voltage drop at the pump (044) by a well respected tuner. If it wasn't necessary, he wouldn't have said it was. No disrespect to yourself, but I'd rather take his word for it than yours.

 

R=pL/A!!!

A 70 AMP wire@77F or 25C as is the normal test temperature, has a volt drop that is less obviously than a smaller wire, but is way more costly and not needed at all under any circumstances for the application, why not go the whole hog and get starter cable from the QE2 ?
The above formula is what you need to know to work out volt drop as well as temperature/length of wire, and of course the wire INSULATION.
If you were top use as an example I gave 28/030 that has a continuous carrying capacity of 28AMPS, pvc insulation, 25AMPS thinwall ie HARDGRADE PVC.
Assuming a length of 20 feet, 10 foot supply 10 foot return, you would have a RESISTANCE of 0.0536 OHMS, which as you know would be a VOLT DROP of 0.6968.
This is at the LOAD that the BOSCH 044 PUMP places on the circuit, by it's rated current consumption(AMPS) at 12VOLTS.
Of course this is an estimation of the length of the wire, if it is less then the RESISTANCE/VOLT DROP will be correspondingly lower still.
If you want to read CRC HANDBOOK of CHEMISTRY and PHYSICS 57th edition, 1976-1977 CRC press, p. F167-168, you would find lots of lovely useful info there.
Now bearing in mind the RATED VOLTAGE of the BOSCH PUMP 044 is 12 VOLTS, and most electrical systems will operate upwards of 12.8 VOLTS, and most nearer to 13.4/13.6VOLTS, one can easily see how 28/030 is more than capable, and a lot cheaper.
Without knowing the LOAD/TEMPERATURE/WIRE INSULATION TYPE/LENGTH etc etc etc etc it can only ever be a guess.
Some guess, and go over board to be safe, spending money unnecessarily on gauge of wire way too large, that is up to them, I prefer not to spend where not necessary, and do it the easier way, using above.
tabetha

 

OMG Tabetha you need to get out more

 

He will when he puts his Saff back together

 

I rewired my fuel pump i just cut the old ignition live wire off the fuel pump relay (yellow relay under dash) n soldered then new wire in from there 2 the fuel pump. I just put the earth from the pump straight the the cars body i drilled a hole in the spare wheel well n used a 10 mm nut n bolt with lock washers n greased bolt.

 

Only got the rad/plugs/fluids to put in then change oil and filter before starting so tuesday with a bity of luck(shopping).
Wish I could get out more, they don't let me out often, the pills are not always effective!!
tabetha

 

will print this off so the technical / mechanical one can read it

i`m the goofer less stress

mr smartiepants ( da bruv ) can`t even turn on a puter he he

will