I have put a new engine into my car. the problem is that the fuel pump is constantly running and keeping the injectors open. It seems to be a relay at fault. I have no wiring loom diagram to work from so cannot make any progress. Can Anyone help?
You have blown up the ecu as a result of not having a good earth connection from the earth lead on the gearbox.
This is a very common problem (done it myself!)
Only solution is to get the ecu repaired or replaced.
You must change the oil and filter before trying to start the car again.
a 6ya Mechanic can help you resolve that issue over the phone in a minute or two.
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If the fuel pump/s continue to run with key on, suspect a relay issue. The relay is grounded by the vehicles computer. If the computer supplies a constant ground, the relay will continue to stay closed and power the fuel pumps constantly. If the the ground wire that comes from the computer to the relay is shorted/grounded, the relay will stay energized as well. As for the no start, are the injectors getting a power and ground supply? The ground side of the injector is controlled by the computer as well. Is the vehicle getting spark at the coil/plug? Have you scanned the computer for any trouble codes?
You would put on a new crank sensor because the ignition system won't work, it gives no spark. So now do you have spark at a spark plug wire end? A blue consistent spark? Probably good ignition system, as long as all spark plugs get a spark.
One thing you always want to check with no start is the fuel pressure. Turning the key to on should turn the fuel pump on and put pressure in the fuel rail at the engine. Autozone and maybe others rent or loan fuel pressure gauges. Multi-port injection systems have high pressure specifications, around 40 psi normally. That is what the injectors require to spray out fuel when they pulse and open the nozzles.
With the injector circuit, the first thing to check is if each injector has power to it with the key in ON. One power wire and one ground wire goes to each injector. The power wire is from a fuse that is powered with key on or key in start, and then it is spliced to all of the injectors. The injector grounds all run into the engine computer, where the circuit can be internally grounded for a split second and cause the injector to pulse. But anytime the key is on, the injectors have steady voltage available to them.
always check for the pressense of fuel and pressure at the fuel rail of the injectors first. you don't give me enough information to diagnose the problem. First thought is clogged fuel filter or bad fuel. 2nd, clogged injectors, bad plugs/wires...sorry can't write a book here...
What do you mean? In the fuel line? In the manifold? In the tank? In the engine/cylinders? Do you want to measure A/F mixture? I am guessing you are asking because your car wont start. I am also guessing it cranks and sputters to try to fire, but never catches and runs. Your 85 VW has three common things I'd check first. 1. The O2 sensor wires crack and the sensor quits working sending the car into limp home mode. 2. the cold start injector at the end of the plenum/intake is a 5th injector that richens the starting mixture until the car warms up... it can fail and the car will run like **** until it warms up and runs on the 4 normal injectors. 3. Before the intake plenum, the can shaped thingy with the metal flap/disc you may have tried jamming a screw driver in or pushing open with your finger is a metal flap that controls and senses incoming air and regulates the idle mixture. It has a few position sensors. Don't poke at this part or you will muck up some parameters that are difficult to re-align. If this is it, take the car to a VW mechanic. That little bugger is a real pain.