Fuel Pressure regulator/fuelpump or Bad CPS??

K, I've done soo much reading my brain hurts..lol. I just bought a '98 XJ w/a cold start problem(and sometimes warm problem if it sits longer than 15 mins). In the morning I can crank it and it willl continuously crank for about 5 sec than stumble and idle fine, but when you put it in gear and get around 1800 RPM it stumbles until you tap the gas and it goes away. The stumble is usually once and doesn't return after you tap the gas... If I let the jeep sit for about 5 mins it'll start up just fine. 15 mins and it takes an extended crank. I also found in both cold and hot situations if you turn the motor over, stop, turn the key back, and prime it, it'll fire up right away. Soo, w/the stumble and hard start could it just be some air in the lines from the bleedback from a bad check valve or a FPR? Or are these symptoms more CPS related?

Thanks in advance guys

What you are seeing is not the crankshaft position sensor. That generally results in a no-start condition, not a long crank condition.

I would suspect either the check valve on the fuel pump assembly located inside the gas tank on your 1998 or possibly a leaky fuel injector which bleeds down fuel pressure and creates the stumble start. Usually though the injector's excess fuel would clear before you get to 1800 rpm though. Low battery voltage has been tied to some long crank times too (sounds weird but it happens).
You may want to start with some fuel pressure testing on the schrader valve on the fuel rail. Verify battery is in good shape. How many miles on your fuel pump assembly??

I believe the fuel pump is the stock one w/165k on it.

Take it to some parts store like Autozone and get a free computer scan to check for error codes. Could be an O2 sensor problem, or even a bad MAT temperature sensor (Air intake, manifold air temp sensor). Might also be some problems developing with the TPS. At some point several parts can get borderline, and the mix of bordorline, nearly bad parts will do odd things at different times.

Has it had a tune up lately, air filter, plugs, wires, rotor and cap?

Gremlins......

A bad engine coolant temp sensor in t-stat housing causes your syptoms also.

cambosoup99 said:

A bad engine coolant temp sensor in t-stat housing causes your syptoms also.

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X2 on the bad CTS. Guess we should mention how easy those two temperature sensors (CTS and MAT) are to test with an ohm meter!

Ecomike said:

X2 on the bad CTS. Guess we should mention how easy those two temperature sensors (CTS and MAT) are to test with an ohm meter!

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:idea: Can you tell me how to test i have a meter and would love to have that info.:clap:

78/xj88 said:

:idea: Can you tell me how to test i have a meter and would love to have that info.:clap:

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With power off, check the disconnected sensor resistance, ohms at ambient temperature, then check it again with the engine hot. Record and post the data here.

I can check the correct values later when I get back. If you search here the correct resistance tables for the CTS and MAT (or IAT) are posted in several Renix threads on sensor test data. But use the words in the search, the search engine here requires at least 4 letters in a word or term. See the FAQ for search methods too. If you can't find it, I will post it later tonight when I get back.