QuestionHi Howard, I'm at my wits end with this one. Hope you can shed a little light on this one. First this is what I've done w/ my 83 XJ6. New plugs, cap rotor, new GM module in amp box. new coil. I get pulsing fire to the plugs. I believe it is fuel related because when trying to start it acts as though it weants to but dies when key is in the run pos. I've verified ign at the coil so I know the switch is good. Fuel pump runs when jumped, also will run in start pos.I've replaced the terminal end on the oil press sens on the pass side of the block, ran great for two days. Now it will start intermittently the die. No sputter, backfire, just die as if the ign was turned off. Are there any other sensors that will affect the ign? If so where will I find them and can they be tested? Getting tired of just throwing parts at it and not getting any reasonable results. I'm almost at the point of doing a GM conversion. Thank you in advance for any input. Steve F.
AnswerHi Steve,
First stop tossing parts at it as you can easily run out of money before finding the problem that way.
Drop back to basics. All gasoline engines only require 3 items to run. Compression, Fire and Fuel. So if it dies or will not start, one or more of the 3 is missing.
If you brought the car to me with the problems you have I would have to do the following.
First I run a compression test (no matter what it's history was, or who just did one ten minutes ago) Only if it passes a compression test on ALL six cylinders do I proceed.
Fire is second. A scope would be best but most people don't have a scope available so the next thing if to put each plug (after inspecting each plug) on it's wire and lay each plug on the head so that the plug contacts the metal of the plug and so you can see the gap of each plug. Then have someone hit the starter and watch each plug fire. The spark should be thick and blue in color. (not is bright sun light). Now put a timing light on #1 or #6 and check the timing as per the specs under the hood. (The sticker under the hood always over rides what the book says)
If you have a good blue spark at all the plugs and the timing is correct, put the plugs back in.
Fuel- The cold start valve supplies extra fuel for starting. That valve is controlled by a Thermo/time switch mounted in the coolant rail with the other sensors. (it is the largest sensor)
The Thermo/time switch grounds the cold start valve only for a short time when the coolant is cold and if you try several times to start the engine the switch has it's own electric heater that disables it after making several tries. (Or when the coolant is warm)
This is to prevent flooding.
Even though the injectors may be firing, they can not supply enough fuel for a cold start.
THERE IS ONE MORE FACTOR THAT IS A (SERIES III JAG ITEM) The ser III Jag requires a "Deep Charge" battery. (diesel or marine battery) and even those in many cases don't last for the normal life of a battery. There is a simple test for this. Even though the battery may be charged and spin the engine over fast and it does not start do this. Get a known good battery to use as a jumper as though you were going to start a car with a dead battery and connect it to the car and try to start it. If it then starts you need a new "deep charge" battery. The old battery can usually be used in any other brand car for a long time. I have used old "deep charged" batteries that would no longer work in a ser. III car in other cars for as long as another two or three years.
If this is not the case and you need to test Fuel now do this. Remove the air filter and put a fuel pressure gauge on the fuel line just before the fuel rail with a "T" and clamps on all joints. Turn on the ignition (not start) and reach in the front of the air flow meter and manually open the flap. You should hear the pump running and even the fuel going through the rail. The pressure at that time should be at or close to 42 PSI. If you have a hand vacuum pump, put it on the pressure regulator and and pump up 15 to 20 in of vacuum and read the gauge. it should read about 32 PSI.
Next test each injector wire with a "Noid" light and spin the engine to see that you have a "Noid" light flash on every injector. ("Noid" lights are very inexpensive and most auto parts stores have them. You need a Lucas or Bosch light.
Now, put the air filter back on and take a can of starter fluid and have someone try to start the engine while you spray a little starter fluid into the intake. If it starts on starter fluid but dies, see if you can keep it running on starter fluid.
If it starts but you can't keep it running put a vacuum gauge on the intake and with the throttle closed spine the engine and note the vacuum as you continue to keep it spinning with the starter. If the vacuum seems to go away as you spin the engine remove both exhaust manifold hex plugs in the side of each exhaust manifold and repeat the test.
Somewhere in one of these tests you have to find the problem.
Howard
