my father in law has a 1998 audi a4 1.8t qt. its been running like crap since me and the woman have gotten together. all of the plugs have been changed the icm has been changed and he took it to a euro tech and the guy found a wire off in the computer and sodered it back together. i was looking at it going through what i thought i could be and i pulled the fuel rail off and turned it over to make sure all the injectors where working right. three of the four are working and the one closest to the fire wall is not working. but if i pull the plug off the one next to it and put it on the one closest to the firewall it will spray. so its not clogded. any one know why the one plug out of 4 would not have power.

 

To start with, I'd check the connector for that injector and look for any signs of damage (heat damage, any melting in the plastic, etc) and if that doesn't pan out, get ahold of a Bentley manual and find which ECU pins that injector's connector is wired up to, and ohm out the wiring - maybe there is damage to one of the wires, so it's not getting the signal to fire. A wire could've broken, been pinched somewhere during maintenance of another sort, or could have been partially melted by something, any of which could keep it from signaling the injector.

 

i have tested the wires with a multimeter and from the front of the car going towrds te firewall. the first 3 going from the front bumper back have .9volts and the one next to the fire wall has 1.6 volts. when the key is turning over. i am gonna trace the wires today and trying to figure this thing out

 

Well you have voltage on the wires, but you may still have damage to one. Measure out the impedance (ohm scale on the meter) between the injector clip and the ECU to make sure you don't have a partial break. You should see only an ohm or two on each wire, since a wire is basically a short between two points. Don't bother with voltage so much at this point - look for impedance. That'll help tell you if you have a broken wire and are just seeing residual or bleeding voltage.

 

so i am gonna put the ground from the volt meter on the battery and the other end on the one wire. its been a while since i tested ohm's

 

Nope - first you need the electrical schematic for the car, so you can find out which pin on the ECU runs to each wire in the injector harness plug. Then put one meter lead on the wire at the injector harness, and the other on the corresponding ECU pin (basically, you're putting a probe at each end of the wire running from ECU to injector). if you have a short (ie, a few ohms or less) then the wire is continuous, with no breaks. If the meter says "OL" or something to that effect, then it's got a break in it. The best thing to do though, is to measure out the bad injector to the ECU, and also at least one good injector, and compare your readings (there may be some impedance in the line that is intentional). If the wires on the bad injector's harness have roughly the same impedance as those on a good injector's harness, then the problem is elsewhere. If you see dramatic differences between the readings from the bad injector and those from a good one, then you're onto the problem, and need to investigate the bad injector's wiring more closely.

 

ok i tested the ohm's today and for the injectors i got .2 ohms. on al four and then i tested the volts comming from the computer to the injector and got 4.9 volts to all but injector number 4 could it be a computer problem. where in ny you live cause i am about 45 mins out side of binghamton

 

I'm in Binghamton (Chenango Bridge to be exact). PM me a phone number and we can talk it over, and see about getting you down here.