Engine Problem/ 2000 JGC

CranK position Sensor? Throttle Body? Coolant Temperature Sensor?

Time to test ign and fuel delivery. ;-)

Just some thoughts!

As I said, I am not a mechanic...... but, coolant temperature sensor causes slow starts and stalls ?

Please elaborate !!

CPS sensor and throttle body problems are valid points I would think...

thanks !!

James

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CranK position Sensor? Throttle Body? Coolant Temperature Sensor?

Time to test ign and fuel delivery. ;-)

Just some thoughts!

My first thought is the CPS (Crankshaft Position Sensor). It's job is to give the computer timing information. Once the engine is running the computer will "guess" on timing if it has to.

Find the connector that runs back to the CPS sensor and unplug/replug it a couple of times. Sometimes corrosion will cause a problem, but they do fail. I've replaced mine once already and it was doign exactly what you describe.

But before doing that, pull the codes and see what the Jeep knows.

after the third switch.

Fuel delivery problems will cause knocking/sag at "wide open throttle". Fuel injection is different from the old carb system where engine vacuum could overcome a failing pump.

The coolant sensor question deals more with long warm-up time. If you have an ohmmeter they are fairly easy to check. The most I've ever had to do with mine was clean the connection.

Yep what Ashton said. The CTS will tell the ECM what temp the engine is at so if the CTS tells the ECM that a cold engine is at normal operating temperature then the fuel will be too lean to easily start that engine. Some engines can start easier if you disconnect the defective CTS, and some not at all.

A good engine scanner plugged into the ECM could tell you the coolant temperature the ECM sees along with other things.

A weak/defective Camshaft Position Sensor could also be the culprit.

Hi James,

I'm not a mechanic either, except for the problems I've corrected on my Jeep.

Some inexpensive things to consider....

#1. check all vacuum hoses (ouch). #2. test the TPS with a volt meter (download your TPS version specs) #3. test the fuel pressure (PSI) from the injector rail.(DL specs)

I really wouldn't think it is the pump because you ARE getting gas, rather maybe the fuel regulator (chump change) at the rail, or even upstream by replacing the fuel filter (more chump change).

You'd be surprised at the havoc a malfunctioning TPS (throttle position sensor) causes.

Ken

1987 Jeep Cherokee / 4.0L / 270k miles

James wrote:

I posted this here on Oct 25, and got **many** helpful replies.

I had the OBD test done, and it showed no errors. Several days after my first post, the problem seemed to have disappeared. I have now put about

1000 miles on the car, and cranked it close to a hundred times, and it now cranks perfectly each time. No stalls/ slow idle/ etc.

What gives ? Could I have had a speck of dirt or trash in the fuel filter and it flushed itself out ? Will the problem likely show up again tomorrow ?? Is the CPS so weird that it can show intermittant failure, and seem to be ok for a while ?

My plan (unless I see stronger advice here) is to drive it and enjoy the ride, and if the problem appears again, to start checking the various problem areas addressed here.

thanks again everyone !!

James

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have a 2000 Jeep Grand Cherokee, 4.7 liter engine. 198,000 miles. Engine has been literally perfect to now.

In the last week, engine has stalled three times, at very slow idle, or very low speed. I have then noticed that all of a sudden, it is sluggish to start. Engine turns over real robustly, but takes much longer than normal to start up.

Engine runs great after start, except for the three stalling occurances in one week. At normal or high speeds, perfect performance. Good pep. No noises.

I am not a mechanic, but I suspect a fuel delivery problem. Perhaps fuel filter or fuel pump ? I have done the ignition switch on and off three times in sequence, but I get no error code. Just reads "done" after the third switch.

In this model, is the fuel pump in the gas tank, as is the case with some Jeeps ? Where is the fuel filter ?

Am I on the right track ?

Any commnents or advice will be appreciated.

James

Keep an eye on the weather. Quite a few sensor problems crop up when it's hot.

They might have also disconnected/reconnected some of the harness. That can clean the crudbunnies that build up.

Well, maybe I reported the problem had disappeard too quickly !!

Although the engine still starts perfectly, all of a sudden this morning I had a very hard time keeping it running at idle. I went through a drive thru for some coffee, and literally had to recrank it about six times to make it through. This was only after about a mile of driving from my home. For the rest of the day it has been perfect.

From my original post, there were many logical suggestions. Two of these were a possible bad CPS, and possible throttle body problem, perhaps needs cleaning. Out of these two, which would you suspect more strongly ?

My OP is quoted again below, but keep in mind that it is starting perfectly now, and has been for about two weeks. After several weeks of running perfectly, I get this slow idle problem again this morning.

Thanks !!

James

-------------------------------------- I have a 2000 Jeep Grand Cherokee, 4.7 liter engine. 198,000 miles. Engine has been literally perfect to now.

In the last week, engine has stalled three times, at very slow idle, or very low speed. I have then noticed that all of a sudden, it is sluggish to start. Engine turns over real robustly, but takes much longer than normal to start up.

Engine runs great after start, except for the three stalling occurances in one week. At normal or high speeds, perfect performance. Good pep. No noises.

I am not a mechanic, but I suspect a fuel delivery problem. Perhaps fuel filter or fuel pump ? I have done the ignition switch on and off three times in sequence, but I get no error code. Just reads "done" after the third switch.

In this model, is the fuel pump in the gas tank, as is the case with some Jeeps ? Where is the fuel filter ?

Am I on the right track ?

Any commnents or advice will be appreciated.

James

I've got the old Renix system, but mine will pull this crap on me twice a year: once in the Fall then again in the Spring. There seems to be a particular range of weather conditions that will make it damned near impossible to pull up to a stop sign without stalling until it gets nice and warm. Never have figured this one out.

If you haven't done it yet, cleaning the throttle body really well is always a good start. I make a pass at all my cars about once a year - usually in the early Fall - and I've seen the throttle body so full of crud that it's a wonder they run at all. Pay particular attention to the Idle Air Control port - even a little buildup in there will cause problems. I've seen that as a common issue on every MPI fuel system I've owned over the last 20 years or so. Just make sure you get a sensor safe cleaner!