Cranks But Wont Start

Discussion in '1994 - 1995 Specific Tech' started by ronstang94, Aug 11, 2014.

  1. I took everything apart to paint the engine bay and install some parts (headers, valve covers, fox throttle body swap). I unplugged nearly every plug that was on the fender aprons so i could move them out of the way to paint everything. I finally got everything back together and the engine cranks but will not start.

    Maybe there is a plug that is not making a good connection somewhere?
    Maybe when I was moving the wires around one of the old brittle wires broke in half?
    Maybe I messed something up with the fox throttle body swap?

    I pulled the #1 spark plug wire off the cap and there is a visible arc to the intake manifold, so I don't think spark is the issue (not a very scientific test).

    I poked the shrader valve on the fuel rail and gas shot out, so I don't think fuel pressure is the issue either (not a very scientific test).


    Anyone have an idea? I really need my car back.

    Thank you :SN:
  2. I should mention that the car ran just fine before I tore it apart. I also checked for engine codes and it shows a 565 (canister purge circuit failure).
  3. Check the TFI and MAF connections.
  4. So, I tested a lot of things last night and everything seems to be correct, but the car still won't start.

    I checked every fuse. I checked for key on engine off voltages at every pin on the CCRM. I checked for 12 volts at the fuel injectors red wire, and a pulsing ground at the black wire. I checked for spark. I checked for fuel pressure, I went over all of the plugs around the engine bay.

    So, there is fuel, spark, and the injectors are pulsing. I did not touch the distributor, so there are no changes there from when it ran just fine before. It seems that everything is there for an engine to run, but nothing. :cry:

    It does backfire out of the intake every so often. It also sounds like a couple cylinders ignite every 4 or 5 revolutions of the crankshaft.

    Out of ideas, so I tried to put my old throttle body back on and rewire my 94-95 TPS sensor back onto the harness and I noticed that the plastic coating on the wires is chipping off in several places along the length of the wires and even down at the base where these three wires meet up with the other wires for the injectors, coolant temp sensor, etc.. I checked for continuity at the ends of the three wires that go to the TPS to see if they were making contact somewhere down below. The volt meter showed continuity between 2 of the wires (I believe it was the brown and the grey w/ red stripe). I wiggled the wires around and tried to separate them, then checked again, and no continuity this time. So, I think I'm on to something.

    Still not sure how this can keep the engine from running though when there appears to be fuel and spark. I'm not the best at electrical and could use some guidance in understanding what is happening here, how to test, and how to repair. The wires are all very brittle and I am worried that if I try to splice on some new wire further back I could just make things worse. A new harness looks like it will cost a few hundred bucks that I don't have, so I am not sure what to do.

    Please help. Thank you :SN:
  5. Have you taken a look at the crank but no start checklist?
  6. Yes I have gone over the Cranks but no start checklist several times as well as the CCRM checklist.

    I saw that a voltage of over 3.7v at the TPS sensor would not allow the car to start and I'm guessing with the wires touching and all, that is probably what is happening. The checklist says that the computer will shut off the injectors to clear a flooded engine when it reads over 3.7v, but the injectors are still pulsing.... so.. is something else going on and the tps wiring is not really the problem?

    I would like to understand how the computer is keeping the car from starting in this situation. Since, it appears that everything for the cylinder to ignite is present (spark at the plug, fuel pressure in the rail, an injector squirting it into the cylinder, ignition timing that has not been touched since it ran properly before, and mechanical valve timing that has not changed either) and it still will not start.

    I also would like to know what my best option is for repairing the wiring harness. Dive in and possibly make things worse? Then just buy a new harness? Where to buy? Make my own?.... Disassemble the car? Burry each piece separately in the desert, so no one can ever find the body?...... This problem is driving me crazy :bang:
  7. IMAG9561.jpg IMAG9562.jpg IMAG9563.jpg
    This is how the wires look. I pulled the engine harness off last night to get a better look at everything. It appears that only the portion of the harness that was near the heater tubes is damaged. I guess the extra heat from the coolant can be really damaging (after 20 years). The drivers side looks just fine.
  8. I was checking for continuity between several different wires on the passenger side of the engine wiring harness. I found a few instances where I had continuity between a couple wires from the same plug (at the fuel injectors, and throttle position sensor).

    So I am going to unwrap that side of the harness and try to repair the wiring. I have some new wire loom, paint on electrical tape, friction tape, and good old electrical tape. I am hoping to just repair the insulation on the wiring rather than replace each wire.
  9. I can't seem to see the pictures, but if you have shorted wires, there could have been damage done to the ECU. Does the damaged section plug into the salt and pepper shakers behind the intake manifold? Your best bet is to replace that harness with another one. Repairing the wiring may cause issues down the road. That area sees a lot of heat and vibration.
  10. That was a worry of mine. Is there any specific tests or ways to tell if there has been damage done to the ECU? Should I be checking for voltage or continuity at any specific wires?

    The 94 and 95 5.0's engine wiring harness is a little bit different than the fox 5.0's. There is just one large electrical plug at the back passenger side of the engine compartment (no salt and pepper). The 94-95 harnesses are much harder to find and a bit more expensive, so I just have to hope for the best.

    If anyone has any advice or links they could share about fixing this kind of wiring issue. It would be greatly appreciated.

  11. I didn't even realize I was in the 94-95 forums. Whoops.

    When you pulled codes, the only one you got was the canister purge?
  12. Yes, only a code for the canister purge circuit failure.

    I pulled the codes after several attempts to start the car. However, since the car never actually started, I'm not sure if the computer even had the time to find any problems (codes), but I am not sure how that works.
  13. I wrapped all of the broken wires in the wiring harness, and even most of the other wires just to be safe. Put everything in a new plastic loom, wrapped it all up, installed it in the car, and put almost everything else back together (I have a couple things jimmy rigged since I am still working some things out for the fox throttle body swap: throttle cable connection and cold air intake). However, I had things together enough to attempt to start the car.... and....

    IT STARTED!!! :D
  14. The engine wiring harness sits right on the very hot engine on both sides. However, only the passenger side wires were crispy. I'm guessing the extra heat from the heater tubes are the cause, although this doesn't really make sense since the engine itself is probably hotter than the coolant. Still, the wires sit between the hot engine and the hot heater tubes, so getting cooked from both sides could be the issue. Also, I live in Phoenix AZ, so it gets hot, it also does not get very cold.

    So, I got rid of these heater tubes and will be replacing the heater core with an electric unit (like what the electric cars use). Cleans up the engine bay quite a bit, plus the heater core was already busted and bypassed (and this will be the second time I pull the dash to fix this thing and want to make sure it is the last).

    So, if you live in a hot climate you may want to check your wires and consider ditching these heater tubes.