91 Laredo

Okay, I finally got around to getting a gauge today (thanks Harbor Freight for a $8.99 sale on the gauge ).

I have had problems with cold starts. Sometimes it will:

1) start okay
2) long crank than stumbles to a start
3) take multiple tries to start

When its warm its fine.

Here are the readings I cam up with (+ / - a psi or so):

Key on only 35 psi
Running with vacume port connected 32 psi
Running with vacume port disconnected 41 psi

Shut it off with the gauge connected went from 32 psi to 40 psi, let it sit for 30 min and dropped to about 20 psi (which I read is acceptable per Haynes)

So... Does it still sound like a fuel issue or should I start looking elsewhere ???

BuckB91XJ

Your fuel pump is fine based on those readings.

91 Laredo

What about the fuel pressure regulator?

Could there still be an issue with pressure leaking off after it sits for long periods?

BuckB91XJ

41 PSI with Vacuum hose disconnected from the regulator is fine. 38-39 is optimum but, I 'd say you were splitting hairs to call 41 bad.

91 Laredo

Okay,

So sounds like both the pump and regulator are fine. Any other ideas?

Done all the other normal stuff (filters, tune up, removed and cleaned t-body and IACV valve, etc...)

Have not touched TPS, MAP, or CPS.

Steveo

i'm leaning toward the cps, i've seen a bunch of these things have those symptoms and a new cps fixed it.

BuckB91XJ

I read through this thread again to prevent asking a dumb question but, did you check or change all of your basic ignition tune-up pieces like the dist. cap, rotor, plugs and plug wires? You can even get your coil and ignition module tested for free at autozone.

91 Laredo

Yes. I replaced the cap, rotor, plugs, wires, air / fuel filter, O2 sensor, removed and cleaned the t-body and IACV valve.

I didnt mess with the TPS as I've read that they need to be adjusted by a shop????

The CPS was replaced at one point by the PO due to a no start and I've read that when CPS's go bad they go completely out at once.

98 JeepJeep

yours sounds like it is doing the same thing as mine...does leaving the key in the on position for a few extra seconds help? i think my issue is due to a leak check valve in my fuel pump allowing the fuel to drain back into the tank. normally if i let it sit for a few seconds if fires right up.

91 Laredo

Leaving the key on / double priming doesnt seem to work much better, but may help a little.

Its just irritating. Fuel injected vehicle should start right up and not have these issues. Damn Jeep.....

91 Laredo

Any other thoughts?

Today I made a specific point to turn the key on and leave it for apprx 30 seconds before I attempted to start. Cranked and stalled. Cranked again and it sputtered and caught idling very low until I gave it some gas then it was fine.

I am about to drive it to a shop or off a cliff....

Sometimes it feels like a choke issue like with an old carb.

lurk520

Damn it... Why isn't this thread concluded... I am having the same issue....Except today for the first time it did not want to turn over.... Crank Sensor has been very recently replaced with a MOPAR part so that shouldn't be an issue... Finally got it to start after an hour and a half of playing with it... had to pump on the gas pedal while cranking and it slowly turned over.... Almost got stranded in Phoenix!!! Then it drove all the way back to Tucson like a champ.... Going to get a fuel gauge tomorrow to try and figure something out....

lurk520

might as well replace my CTS as well....only costs about 17$

tjwalker

There is no adjustment on the TPS for 91 and newer, but they can and should be tested when symptomatic. This does not sound like a crank sensor. Here is more on the TPS.
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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

 Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
 High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
 Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
 Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
 Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

lurk520

So I went to Auto Zone today and rented a fuel pressure test kit. Came with the pressure gauge and also a multi-meter. Fuel pressure checked out OK. Read in my Haynes the CTS should read 7,000 ohms or greater when engine is cold, guess what it read about 4,200, checked the new CTS it was about 7,200. So hopefully this was the culprit! Damn I'm feeling smart! Now this thread has some kind of solution for the next poor soul!