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HELP NEEDED!! from the 4.0 gods!!

dodgethis12

NAXJA Forum User
Location
Virginia
Ok so I've been working on the 93. Started off I bought it it was running super super rich...

so rich that I discovered the cracked manifold as raw gas was running out of the crack and dripping in the floor off the exhaust pipe ! OOuch!

So I pulled the intake and exhaust manifolds and fould the exhaust cracked in 2 spots.... around the #4cyl where it connects to the body of the header and then the top tube of the collector as it sits on the jeep. Cleaned it up real good and welded it up.... looks good.

Put it all back together.... no leaks.... but still running super super super rich. Within 30 seconds I had to shut it off and vacate the shop with all doors open (25 degrees outside!! :(

I had originally thought the cracked manifold was screwing with 02 senser causing it to make it run rich, but the now the manifold is fixed... it hasnt changed!

Please help!!

Its a 93 4dr 4.0 auto 120K.

I have pics of the regulator/injector style if someone want to put them up for me (cant from work)

Thanks
 
I would check the specs on the fuel pressure regulator, and replace the O2 sensor. Do you have a check engine light on???? If so get the codes read before replacing anything.
 
Thats the strange thing...... theres no CEL on!!

The pressure regulator is located at the front of the rail with 2 allen screws and a vacuum connection correct?
 
super(X3) rich condition would result from
1. too much gas into the combustion chamber
--I'd check the MAP sensor vacuum source to see that it's getting correct
vacuum
--fuel pressure to make sure it's not too high
--fuel pressure after shutdown to make sure there's not an injector leaking
--coolant temp sensor to verify it's not reading too cold

2. unburned fuel exiting the combustion chamber
--verify all plugs are firing consistently
--air filter is allowing enough air to enter and atomize the fuel
 
First things first. Go old school. Pull the plugs and look at them. If nothing else, post pix up. The plugs will tell you more than just about anything.
 
OK so here is the parts list:

New plugs....its been running rich so im sure they are all fouled up

new regulator

new 02 sensor

Where is the map sensor located? Which temp sensor controls the computer? Theres one on the front of the engine and one on the rear.

Thanks for all your help guys.....
 
OK so here is the parts list:
New plugs....its been running rich so im sure they are all fouled up
new regulator
new 02 sensor
Where is the map sensor located? Which temp sensor controls the computer? Theres one on the front of the engine and one on the rear.
Thanks for all your help guys.....

plugs- yes (cap. rotor, wires, too)
regulator- check pressure first
O2 sensor- yes

MAP located on the firewall above and too the drivers side of the valve cover (3 wire and one vacuum line)

temp sensor fro the ECU is in the thermostat housing
 
Ok, RAW fuel dripping out of the exhaust?

My money is on the pressure regulator and/or bad injector, and maybe but not likely a bad synch sensor in the distributor or the PCM.

You may have damaged the o2 sensor and CAT from the raw fuel.

I don't think a MAP or o2 sensor can cause raw fuel to run out of the exhaust.

Also, your oil is most likely contaminated and needs changing.
 
If you do the plug reading, it will show if the problem is system related, ie a sensor, or if it is limited to a single cylinder, ie bad injector.
 
If no CEL is coming on, I'd vote for either high fuel pressure or a mechanically bad injector or both too, because this is something the OBD cannot detect. I've had a bad sync sensor on both a 93 and a 95, and they both set the CEL with the correct code, and both failed to start without pulling the connector plug and replugging it while the ignition is on. You can get home that way if it strands you. The engine can run with a bad sync sensor, and may overheat and stumble a bit from the scrambled injector timing, but mine didn't smoke.
 
Please elaborate on the sync sensor.... I am unfamiliar with this or what it does.... strange that I've never heard of this on other vehicles, or maybe I know it by something else.

I will pull the plugs and check them to see if it is isolated to a single cylinder....
 
Please elaborate on the sync sensor.... I am unfamiliar with this or what it does.... strange that I've never heard of this on other vehicles, or maybe I know it by something else.

I will pull the plugs and check them to see if it is isolated to a single cylinder....
The sync sensor is the electronic innards of the distributor. On many vehicles this would be the ignition timing gadget, but on the XJ ignition timing is done by the flywheel and crank position sensor. The sync sensor sets the timing for injectors. In my experience, at least, when the sync sensor fails on the OBDI system, it will set a code 54 and fail to start. When this happened the first time on my stepson's 93, I found by accident that the vehicle can be started and driven, by turning on the ignition, then unplugging and replugging the distributor connector. The PCU then finishes booting up, and you get one start. The procedure must be repeated every time you start. When the same thing happened again on my 95, I drove it home a few miles this way, and it got me there, but ran less than perfectly, and appeared to be overheating a bit, though the latter is not certain - my 95 tends to burble and fuss after shutdown anyway. I suspect the untimed injection messed with the mixture, but it did run, and did not flood or smoke. As I recall, MPI fuel injection is usually timed to fire just before the intake valve opens. The original Bosch Jetronic was designed on purpose to hit the valve stem before it opened, I guess to aid in vaporization.
 
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