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code 27 has me stumped!

ceasar

NAXJA Forum User
Location
oregon
so shortly after overheating my 1994 XJ 5 speed it started shutting down at anround 150 degrees and wouldnt start till cooled down...codes came back as CPS and TPS.replaced those....same thing.so i just went ahead and replaced it all... temp sensor,ASD relay,PCV,distributor cap and rotor,Map,o2 sensor.still the same issue with code 27 everytime.checked all connections multiple times and checked that injectors are firing at right voltage.all good.so i figured it was the ECU.tried two different ones with the same problem.so i am Horrible at electrical but it seems like i got a bad wire from the ECU to an injector?!!!1
i am stumped....any help is much appreciated.
 
I think Blake is on the right track in suspecting the cam sensor. Code 27 indicates a loss of injector signal which the cam sensor regulates. They're very easy and relatively inexpensive to replace. (Five minute job, tops.)

I've had two failures of these puppies on two different XJs. On the last one, I added extra epoxy to secure the magnet better.
 
As I remember it there is a split in the years for the cam sensor in the distributor the early HO 4.0 (91-92-??) require the removal of the distributor to swap the cam sensor and later designers are simpler to replace.

Hopefully the 94 is the updated design, I believe those of us with the old PITA distributors can swap them out for the newer distributor. I think the plug for cam sensor stayed them same for more of the HO 4.0 run.


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just put in the pick up coil and it did the same thing!!:firedevil the CPS still checks out good and have spark after it dies but not start back up till cooled down:smsoap:
 
When it dies can you put on a fuel pressure tester on and see if it's get fuel pressure? Or spray some tb cleaner down the intake and see if it will run? If it fires with the tb cleaner then there's a fuel delivery issue. If that's the case start with basics. Fuses and verify the relay is holding contact after its hot. Also, is it possible this may be a heat soak issue on the fuel rail? Maybe someone else can chime in.


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Do you still get the code 27 with the new cam sensor?

Sorry the sensor didn't fix it. Good suggestions from Blake
about fuel delivery.

Maybe the A/C relay can be swapped with the fuel pump relay
to check...?
 
Back to basics, when it heats up to 150 and the motor shuts down, test for fuel pressure while cranking. Then test for spark.

Two things I've found that may kill an engine when it goes from open to closed loop (around 150) is a faulty O2 sensor. O2 sensors can be mostly failed and not throw a code. O2 sensor wires burning on the exhaust in the rear or the exhaust manifold in the front is often a possibility.

Check the supply voltage to the CPS circuit, some sensors share a supply voltage. When one sensor partially shorts out it can draw the supply voltage down so low other sensors on the power supply tree give faulty readings. The fix is simple, unplug the sensors one at a time and see which one is drawing the supply voltage down, unless it is a shorted wire then it gets more difficult.

And lastly ignition coils are known to be heat sensitive, a visual spark check will usually tell you if it is a coil. They can completely fail or partially fail. A partial failure usually causes a very weak spark.

I've had poor luck relying on the CEL codes, low supply voltage, for whatever reason, gives faulty or irrelevant codes.

I'm not sure if your sensor supply voltage is 7 or 5 volts it is usually one or the other depending on year.

I'v never seen it but it seems probably a shorted injector could be over heating the injector drivers and they are shutting down. If my other suggestions don't help, Ohm test the injectors. They should all have about the same Ohms, if one is way low or zero Ohms you have found a problem.

I've changed one sensor on a hunch in the last 30 years and I was wrong. Now I test.
 
switched the ac relay for fuel pump no change.jeep still starts after dying but quickly dies.no new codes.the TB spray trick did not work but i am going to oreillys to borrow a tester anyways.
 
Does it still die if you hold the throttle open? When it dies does the rpm just drop to 0 or slowly go down. Also just for good measure make sure that the O2 and Crank sensor wiring is not shorting on the exhaust manifold.

Also isn't code 27 an injector fault code? Can you check that your injectors are maintaining 12v feed while it dies.
 
When it gets up to 150 degrees and the issue starts verify spark, injector signal and test the resistance of the injectors. My guess is when you over heated you messed up an injector or 2. The resistance may be bad enough its also causing the driver to shut down.
You can keep taking the parts shotgun approach but you are just spending money and not finding the problem.
 
well thats the damndest thing ....put a pressure gauge on it and it read 30 PSI the whole time and went up to operating temperature without stalling.i am cunfused now...
 
Intermittent problems are the hardest to find.

Just to eliminate it, jump the ballast resistor. Possible after it heats up it may make iffy contact or develop high resistance, seen it before on earlier models.

Another possibility is your fuel pump gets iffy after it heats up.

But my best guess / is a WAG (wild assed guess) is your O2 sensor wires are cooking on the exhaust manifold. Something to especially look at if you've swapped out a water pump any time recently, it is easy to route the wires wrong and cause them to cook.
 
i took it for a short drive today....literally a block and half after it warmed up and it died
again.had to keep into the throttle while half clutched just to get it back.it stunk so bad of clutch so probably thats next.....
 
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