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Hey everyone, I tried doing a forum search but I couldn't really find an answer to what's going on. My 1993 XJ6 I just purchased won't start. She cranks but won't fire. So I went through the basic checklist. Power, yup new battery. Spark, yup nice and strong. Fuel, Nope. So I tested it. Fuel pump relay is working.. If I apply 12v directly to the pins on the evap cap it runs strong. If I disconnect that little harness to the evap cap that plugs in behind the battery and apply power, the fuel pump runs. If I jump the fuel pump relay I have 12 volts at the plug to the evap lid, but the pump will not run. I've checked all the wiring for continuity and it all checks out. Part of me was wondering if it was the zener diode and capacitor, but then I can't explain how that jumper harness would run the pump when I disconnect it from the vehicle harness and apply power to it. Anybody have any thoughts? I haven't had the chance to drive the car yet. Thanks, Michael.
Congratulations on your 1993 XJ6! I owned one for 16 years and loved it.
There are a lot of possibile causes of your problem.
You seem to have confirmed the integrity of the B+ side of the wiring between the relay socket and the fuel pump. Thinking through your description, the first suspect that comes to mind is the ground side of the circuit between the connection behind the battery and it's ground point, which is below the right rear Bulb Failure Module (BFM) near the tail lamp.
You can download the wiring diagrams for your car here:
Ok, so after alot of searching and diagnostics, I've got no power to my injectors. My understanding is that there should be 12v to the injectors with the key on and then the ECU closes the ground which fires the injector. Is this correct? My other understanding was that the fuel pump relay and ignition are controlled by the ECU as well, and those are both working? So what could be causing the problem?
Ok, so after alot of searching and diagnostics, I've got no power to my injectors. My understanding is that there should be 12v to the injectors with the key on and then the ECU closes the ground which fires the injector. Is this correct? My other understanding was that the fuel pump relay and ignition are controlled by the ECU as well, and those are both working? So what could be causing the problem?
Hi Michael,
The document below explains the fuel injection on your '93. Both the power and ground wires of the coils connect to the ECM. The ECM opens the injectors with a large "turn on" voltage pulse, then holds them open for the required duration with a series of lower-voltage "hold on" pulses. It may be that the ECM pulses the ground side rather than the B+ side. All injectors are pulsed simultaneously. You may not be able to read the pulses without an oscilloscope.
Did you check the ground side of your fuel pump? What about all the voltages and ground continuity from the fuel pump relay socket? Are you getting control voltage from the ECM at the fuel pump relay socket?
Don, I feel a bit silly (it's been a long day), I had my meter on the wrong setting. :/ I do have 12 volts to the positive side of the injectors. I also had someone try cranking the car while I used a stethoscope to listen to the injectors, and none of them were clicking. I have plenty of fuel at the rail, but it's just not getting into the cylinders. I did however get "Fuel Fail 33" on the VCM today. My understanding is this means there is a short or open circuit in the injector system somewhere? I unplugged the ECU and all of the injectors and checked continuity. It is good between the ECU and the Injectors, and it's not shorting anywhere that I could find as my meter showed no continuity between the chassis and any of the injector wires. I tried resetting it via the reset button, but it comes back on almost instantaneously. Does this mean my ECU is bad?
Originally Posted by Don B
Hi Michael,
The document below explains the fuel injection on your '93. Both the power and ground wires of the coils connect to the ECM. The ECM opens the injectors with a large "turn on" voltage pulse, then holds them open for the required duration with a series of lower-voltage "hold on" pulses. All injectors are pulsed simultaneously. It is doubtful that you can measure these pulses without an oscilloscope.
Did you check the ground side of your fuel pump? What about all the voltages and ground continuity from the fuel pump relay socket? Are you getting control voltage from the ECM at the fuel pump relay socket?
Cheers,
Don
Lawrence, if you re-read my original post the fuel pump relay was working exactly as it was supposed to. The fuel pump not powering up turned out to be a bad solder joint in the fuse panel. Now I just need to figure out why the injectors aren't firing. :/
Originally Posted by Lawrence
Just to add to the mix - the oxygen sensor heater relay on the firewall will prevent the fuel pump from operating if it is malfunctioning.
Larry
Last edited by michael.zerishnek; Dec 13, 2020 at 06:43 PM.
I do have 12 volts to the positive side of the injectors. I also had someone try cranking the car while I used a stethoscope to listen to the injectors, and none of them were clicking. I have plenty of fuel at the rail, but it's just not getting into the cylinders. I did however get "Fuel Fail 33" on the VCM today. My understanding is this means there is a short or open circuit in the injector system somewhere?
You may have triggered the FF33 when you disconnected injectors to test for voltage. The reset button does not clear diagnostic trouble codes (DTCs). A quick way to do it on your '93 is to turn the key to position II (Ignition ON) but do not start the engine. Remove fuse #9 (I think - second fuse from left) in the center console fuse box. Watch for the speedometer and tachometer needles to drop below zero. Replace the fuse and turn the key off for about 10 seconds. Then check the VCM again to confirm the code is cleared. If you have multiple DTCs, you can read them in this manner, clearing each one after you've read and recorded it.
When you say you have plenty of fuel at the rail, have you actually tested the fuel pressure? This usually requires special metric fittings to adapt most common fuel pressure gauges to the rail.
How is your battery? Low battery voltage, especially while cranking the engine to start, can cause all manner of difficult-to-diagnose gremlins.
You may have triggered the FF33 when you disconnected injectors to test for voltage. The reset button does not clear diagnostic trouble codes (DTCs). A quick way to do it on your '93 is to turn the key to position II (Ignition ON) but do not start the engine. Remove fuse #9 (I think - second fuse from left) in the center console fuse box. Watch for the speedometer and tachometer needles to drop below zero. Replace the fuse and turn the key off for about 10 seconds. Then check the VCM again to confirm the code is cleared. If you have multiple DTCs, you can read them in this manner, clearing each one after you've read and recorded it.
When you say you have plenty of fuel at the rail, have you actually tested the fuel pressure? This usually requires special metric fittings to adapt most common fuel pressure gauges to the rail.
How is your battery? Low battery voltage, especially while cranking the engine to start, can cause all manner of difficult-to-diagnose gremlins.
Cheers,
Don
Don, the FF33 came up before I unplugged the Injectors. I guess I should say I assume it has good fuel pressure, as the pump is definitely working and moving alot of fuel. To help flush the tank out I had disconnected the line from the fuel rail and run a clear tube into a fuel can to see what the fuel looked like. The battery is brand new. I put it in last week the day after I bought the car.
The battery is brand new. I put it in last week the day after I bought the car.
But what's the voltage while cranking? Corrosion on the battery power connections and ground connections throughout the car can pull your voltage down, and of course repeatedly cranking an engine that won't start will discharge the battery.
Well I think it may be something wrong with the ECU. The injectors definitely aren't firing. I have 12 volts to the positive side of the injectors. When the car is being cranked I can't feel or hear the injectors clicking. Battery has a full charge as I've been keeping it on a tender. This evening I pulled all 6 injectors, and if I apply power to them they each click. Here's a a checklist of what I did to come to that conclusion. If I missed something let me know.
1. Disconnected the battery, ECU, and the injectors
2. Tested for continuity between the positive side of each injector and their respective terminal on the ECU connector. (Tested good)
3. Tested for continuity between the negative side of each injector and their respective terminal on the ECU connector. (Tested good)
4. Tested for continuity between the positive side of each injector and the chassis to check for shorts. (No shorts found)
5. Tested for continuity between the negative side of each injector and the chassis to check for shorts. (No shorts found)
6. Pulled the injectors to test each one. (All 6 passed click test when I tapped wires to a battery.)
So am I right in assuming that it does look to be an ECU failure as there appears to be nothing wrong with the harness?
What does the rev counter indicate when cranking? It should show about 200 rpm - AFAIK if the CPS isn't working properly, the injectors won't squirt, because they won't know when to do that.
What does the rev counter indicate when cranking? It should show about 200 rpm - AFAIK if the CPS isn't working properly, the injectors won't squirt, because they won't know when to do that.
That's a great question, Larry, but in his first post, Michael stated that he had strong spark, which is another thing he wouldn't have if the CPS were bad. But that doesn't mean his CPS isn't delivering an erratic signal.
Originally Posted by michael.zerishnek
Spark, yup nice and strong.
So Michael, how does the tach read while cranking?
My car had to be flat-bedded home this summer as IT wouldn't start (first time ever) because the rotor had very high resistance.
Rotors on these cars have a potted component between the centre and the sweep that can fail - preventing the car from distributing the spark, even if you have "strong" spark at the coil, however the injectors should still pulse with a failing rotor.
OTOH, a failing or intermittent CPS circuit/connection is generally the primary cause of a no-start condition. This component, if NFG, will prevent the injectors from impulsing. Check/clean the connection of the large connector at the ECU and also check the body and engine ground points.
Another Crank No Start Car
