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westrope65
westrope65, ASE Certified Technician
Category: Car
Satisfied Customers: 404
Experience:  ASE
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1991 JEEP CHEROKEE: ACCELERATE..FUEL PUMP..NEW REGULATOR; NEW TUNE

Customer Question

I HAVE A 1991 JEEP CHEROKEE THAT WILL NOT ACCELERATE PROPERLY. WE HAVE NEW FUEL PUMP; NEW REGULATOR; NEW TUNE-UP PARTS AND STILL HAVE PROBLEMS. THE EXHAUST MANIFOLD TURNS BEAT RED INSTANTLY. DO YOUR EXPERTS HAVE ANY SUGGESTIONS FOR WHY IT MIGHT DO THIS. IT IS A 4.0 6 CYLINDER ENGINE IN THIS JEEP CHEROKEE.
Submitted: 6 years ago.
Category: Car
Expert:  westrope65 replied 6 years ago.
Hi, welcome to Justanswer.com

I would definitely suspect the crank position sensor. (testing at the end) This si why your timing is off and sending fire down the exhaust. But lets get the OBD or on board diagnostics. They can often point in a good direction.

Here is general procedure for getting engine codes by using the flash method.
Turn the key from off to on three times within five seconds. Then watch the CHECK ENGINE lamp. When you hit the proper rhythm ( this varies some from vehicle to vehicle and takes a few tries sometimes ), the MIL will stay lit longer than normal, go out and then start flashing.
Count the flashes. There will be short pauses between sets of flashes to indicate you're going to another number. The last set of flashes will always be 5-5, or code 55, which means end of test. All the codes will have two digits to them. You can repeat this as many times as needed to get a feel for how it works. If the PCM or battery has been disconnected within the last month or so, the first code you'll see is 1-2 (code 12) which indicates a recent loss of memory. be careful not to misread numbers so like 1-2 becomes a 3 or 2-3 becomes 3-2. Do this a few times to check and always write them down for future reference.
Remember these codes do not say parts are bad only that they got or receive a bad signal. SO it maybe part before or after them that needs to be replaced.
Most parts stores will scan for codes for free. (if we can not get them form the key method first) Then come back to this question. Let me know what they get and we can look for correct component. If it says something differet then crank position sensor We can look there.

TESTING
Disconnect the engine speed sensor electrical connector from the wiring harness. Check the resistance of the sensor by placing an ohmmeter across terminals A and B (marked on sensor connector). With the engine at normal operating temperature, the ohmmeter should read 200 ±75 ohms. Replace sensor if ohmmeter readings are not within specifications.

The crankshaft position sensor is mounted in the transmission housing at the rear of the engine block.
graphic

REMOVAL

  1. Disconnect the Crankshaft Position Sensor (CPS) electrical connector.
  2. Remove the CPS mounting screw.
  3. Remove the CPS.

INSTALLATION

  1. Install the CPS flush against the opening in the transmission housing.
  2. Tighten the CPS mounting screw.
  3. Connect the electrical connector to the CPS.


hope this helps.______________
PLEASE CLICK ON "ACCEPT" IF I WAS HELPFUL-OR IF YOU NEED FURTHER ASSISTANCE JUST ASK, THANKS
westrope65, ASE Certified Technician
Category: Car
Satisfied Customers: 404
Experience: ASE
westrope65 and 9 other Car Specialists are ready to help you
Customer: replied 6 years ago.
WE HAVE A SNAP ON 2007 SOLUS SCANNER AND IT REVEALS NO CODES IN THE MEMORY OR NO CHECK ENGINE LIGHT IS ON. WE HAVE NOT REPLACED THE CRANK SHAFT SENSOR BECAUSE THE VEHICLE DOES RUN GOOD AT AN IDLE. WOULD THE SENSOR STILL BE BAD IF IT RUNS?
Expert:  westrope65 replied 6 years ago.
it is possible to run well and not have problems at idle. It should send a code either way. Try the key method I described also. SOme of the newer scanners look for the newer codes that were made all the same for 2004. Of course that is roughly. So use that as a double check. Did you try the vot/ohm meter testing i sent? ON occatoin it is possibel to ruin a flex plate and teh plate is crakced and flexes missing signals but it is rare. Doing so worse at higher speeds.
Customer: replied 6 years ago.
WE HAVE DONE EVERYTHING YOU SUGGESTED AND IT IS NOT THE CRANK SHAFT SENSOR, IT IS FUNCTIONING PROPERLY. THE ENGINE WAS JUST REBUILD BY AN ENGINE BUILDER, IS IT POSSIBLE HE ASSEMBLED SOMETHING WRONG? WE HAVE LOTS OF FIRE, GOOD FUEL PRESSURE BUT WON'T ACCELERATE. WE HAVE TALKED DIRECTLY TO A JEEP DEALERSHIP AND WERE UNABLE TO HELP US EITHER. IS THERE ANYTHING ELSE YOU CAN THINK OF THAT MIGHT CAUSE THIS VEHICLE TO HESITATE OR NOT ACCELERATE?
Customer: replied 6 years ago.
WE ARE DOING YOUR TEST RIGHT NOW WE HAVE CODES 12 14 27 54 55; PLEASE ADVISE IF YOU KNOW WHAT THEY MIGHT MEAN? THANK YOU SO MUCH
Expert:  westrope65 replied 6 years ago.
12 Battery or computer recently disconnected will occur on most cars most of the time, it indicates a low / missing battery happened in the last 50 key starts
14* MAP sensor voltage below .16V or over 4.96V
27 Injector circuit isn't switching when it's told to (TBI)
OR (all 1990-) injector output driver not responding
- check computer, connections
54 No sync pickup signal or camshaft sensor/distributor timing
55 End of codes

that is what the codes are for
Expert:  westrope65 replied 6 years ago.
manifold turning red is timing off and throws open exhaust valve firing down the exhaust manifold. So it seems to point to cam sensor being bad
graphic
graphic
Expert:  westrope65 replied 6 years ago.

14* MAP sensor voltage below .16V or over 4.96V
* Activates Power Limited/Check Engine light on some models.
Expert:  westrope65 replied 6 years ago.
TESTING
graphic
NOTE: Before starting the test, check the condition of the electrical and vacuum hose connections. Repair if needed.

1. Turn the ignition switch ON (the engine should remain off), and test the voltage from connector terminal B to ground with a voltmeter. Voltage should be between 4 to 5 volts. With the engine started, warmed to normal operating temperature, and idling, the voltage output should drop to 1.5 to 2.1 volts.
2. Check for voltage at the engine controller electrical terminal 5 under the same conditions as in step 1. The voltage readings should be the same as in step 1. If the voltages are different, then the wiring harness should be suspected as the problem area.
3. Check the supply voltage to the sensor by connecting a voltmeter to connector terminal C and a ground. Voltage reading should be 5 +/- 0.5 volts with the ignition switch ON. There should also be 5 +/- 0.5 volts at the engine controller electrical terminal 6. Repair wiring harness if necessary.
4. Check the sensor ground circuit between electrical terminal A on the sensor and engine controller connector terminal 4. Connect one lead of an ohmmeter to electrical terminal A of the sensor and the other to SBEC II connector terminal 4. The ohmmeter should indicate continuity. Repair wiring harness if necessary.
5. Check the sensor ground circuit at the engine controller electrical connector. Connect an ohmmeter between terminals 4 and 11 of the engine controller electrical connector. If the ohmmeter does not indicate continuity, check the sensor ground connection at the right side of the engine block behind the oil dipstick. If the ground connection is good, replace the engine controller. WARNING: If the engine controller connector terminal 4 has a short to 12 volts (battery voltage), this is most likely the reason the first engine controller failed; consequently, it is imperative that this circuit be repaired before installing a new engine controller.
Customer: replied 6 years ago.
WE WILL CHECK THIS OUT AND DO YOU ALSO HAVE A TEST FOR THE DISTRIBUTOR?
Expert:  westrope65 replied 6 years ago.
ok
Ignition timing is electronically controlled by the Powertrain Control Module (PCM) and is NOT adjustable.

Adjusting the distributor will NOT change the ignition timing. It will change the fuel system synchronization and can cause driveability complaints. Refer to TSB's if the vehicle exhibits surging, bucking, intermittent missing or other driveability symptoms.

If you are installing the distributor for the first time (I.E. during and engine rebuild), refer to Distributor/Service and Repair for distributor installation procedures.

So you can get some adjsutment for the timing of the injection pulse with the toe clamp of the distribor. But it is best left alone. You can get signal from the distributor I do nt have volt/ohm test for that.
Customer: replied 6 years ago.
WE HAVE TRIED REPLACING THE DISTRIBUTOR A FEW DAYS AGO AND PURCHASED RMFD FROM NAPA AUTO PARTS, BUT WHEN IT WAS INSTALLED WE COULDN'T GET THE VEHICLE TO EVEN START. SO WE DETERMINED IT MUST BE DEFECTIVE BECAUSE WE PUT THE OEM DIST BACK IN AND IT FIRES RIGHT AWAY, JUST NO ACCELERATION. WE WILL TEST THE COMPUTER, BUT IT DOES BACKFIRE THROUGH THE INTAKE NOT THE EXHAUST, IS THIS STILL TIMING?
Expert:  westrope65 replied 6 years ago.
in your post you said exhaust manifold gets red hot? that is not intake? it woudl be doing both if the physical timing was off if it fires down ehaust it fires up intake. and with no codes it is eitehr rfuel related OR physical timing is off. YOu can get a minor adjsutment for timing of the injection pulse with the distributor. Form the cam sensor inside you can have minor problems with injections timing. BUT it should run with this unplugged even. especially when started.

What were the voltage results on your MAP test? also?
Customer: replied 6 years ago.
thank you for your help, you seem very knowledgable.
Customer: replied 6 years ago.
THE ONLY REASON WE HAD A MAP SENSOR CODE WAS BECAUSE WHEN WE WERE CHECKING ALL OUR SYSTEMS WE UNPLUGGED IT TO SEE IF IT WOULD CHANGE OUR PROBLEM, IT DIDN'T SO WHEN WE RESET CODES THAT ONE WENT AWAY.
Expert:  westrope65 replied 6 years ago.
ok
Customer: replied 6 years ago.
I WOULD BE WILLING TO PAY MORE MONEY IF YOU CAN COME UP WITH ANYMORE OPTIONS FOR US?
Expert:  westrope65 replied 6 years ago.
I can help you will have to tell me what you need.

YOu have checked the physical timing for the CAM and the crank. Correct?

Your crank positoin sensor is new and tests good.

Cam sensor tested good. (pick-up coil) shoudl be able to run with out this once started. then it runs on memory fo the PCM.

The flex plate is not cracked and wobbling? Sending a bad signal.

PCM that can be tested. I do not know how much but ALWAYS have it tested. if it tests good look for wires shorts and connectors corroded. Also I mark mine with a dot or tow of nail polish to guarentee I get mine back. Learned that the hard way.

Wiring??

Bad physical cam or valves??

Coil but that is new correct?

i am running low on ideas. But I am here if you need anyting


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