jepswagon

My alternator died on me. After I got it changed I started my Jeep and it ran fine. When I went to restart it again it flooded and would not start. Now if it sits for 24 hours and is cold, it will fire right up using no gas pedal. And only sometimes I can wide open throttle and it will start. I tested the throttle position sensor and it failed in closed mode. all I could do was put 1 on from the junkyard, but it passed the volt meter test and i thought I was good to go. but now the problem is back. Am I still dealing with a bad throttle position sensor? figuring that the junkyard one isn't in good shape. When it does start, itruns awesome lots of power and fuel everything except for a stumble right off idle

jtm01xj

Test for fuel pressure it could be a fuel issues

tjwalker

So starts fine COLD, but not WARM? Must verify this is the case.

I certainly don't disagree with checking fuel pressure, but if that checks out, the throttle position sensor is not out of play. I buy my TPS sensors directly from Jeep; NAPA is my 2nd choice.

The other thing that comes to mind is a faulty coolant temperature sensor. Located on the thermostat housing. That can result in faulty data to the computer resulting in either difficult cold or hot starts, depending on how the sensor fails. It is not an expensive sensor and it is easy to replace; something to consider.

jepswagon

So far I've tested 3 different throttle position sensors that I have on vehicles and they all read the same 0.75 closed n smooth all the way up 2 to 3.75 wide open throttle. Then I tested my feel pressure and pressure regulator. They test good. Is the fuel pressure supposed to be a 40 pounds while cranking the engine over to start? My engine still stalling at idle when I touch the gas and if I shut it off after warm it floods unless I hold the gas wide open. I believe my water temperature sensor is working properly it responds when the engine warms up very consistently. What should I test now? ignition system?

tjwalker

What year/engine is your XJ? Always best to lead with that information when you start a thread.

Plenty of significant differences through the years. Fuel pressure specs to mention just one. And earlier models had 2 coolant sensors; one for the gauge and one for the computer. So if your vehicle falls in that category, you can still have proper coolant temp on your dash gauge, but the wrong input to the computer.

jepswagon

thought I put my info in. oops. 1992 4.0 ho multipart injected

tjwalker

The coolant temperature sensor that you would be suspect of would be in the thermostat housing if I remember correctly. The one on the back of the head controls the dash gauge.

So again, just because the dash gauge reads properly does not mean the computer is getting proper data.

For a 92, you should have 31 psi of fuel pressure at idle. Then you need to disconnect the vacuum line leading to the fuel pressure regulator (be sure that the line is pulling good vacuum and is not wet with fuel) and the pressure should jump to approximately 39 psi.

Start with the above...............

jepswagon

i did the vacuum test on the regulator. no fuel anywhere and the pressure is perfect both attached and detached vacuum. I will get back to you after I test the temp sensor tomorrow.

jepswagon

so, I tested the temp sensor in the thermostat housing and it read "open circuit". wouldn't that be a bad temp sensor? I thought it was strange that the OBD never spit out a code for that sensor. Also what about the idle air control motor? my idle was running hi for the last month. an angle I am working on is the pcm. Mayne it going bad. Because my auxiliary fan quit but has a good relay,ac system hasn't work since I bought it, speedo don't work and now with the flooding and no start. AARG!