I have a 94 Discovery with 195,xxx miles that starts and runs great, except from time to time it won't start after being driven and then turned off. I have recently replaced the spark plugs, o2 sensors, throttle position sensor, and cleaned all grounds.

I have noticed that the vehicle runs rich at idle. When trying to start warm, it will crank very strong, but just wont catch. After waiting a couple minutes sometimes it starts right up... other times I have to give it throttle for it to start. At it's worst it has taken repeated attempts over an hours time to get it to start.

This problem has not thrown any codes and has been going on since before I replaced the above parts. The above parts were needed to fix other issues I had, But this one's got me stomped (fuel temp. sensor, coolant temp sensor, or fuel pressure regulator?).

 

This is merely a general rule of thumb but it could be a combo of things. If you have a hot start issue it could be the Fuel temp sensor. With a multi meter (if you own a '94 it is a must) pull the plug off the temp sensor (on the left side of fuel rail, under plenum intake, below the TPS). check continuity (ohms, resistance) and the following chart details the ohms you should see at the corresponding temps:

32*F (cold as hell) 5700 - 5900 ohms
68*F (livable temp) 2400 - 2600 ohms
104*F (warm fuel rail) 1100 - 1300 ohms
212*F (friggin hot) 150 - 200 ohms

notice the pattern... as the thermistor cools resistance goes up. IF your sensor is bad and giving high resistance readings the ECM will think the Engine is cold and will fuel it (rich) accordingly.

 

Thanks I will check that tomorrow night. Any other tests to rule out other parts would be appreciated.

 

Ran the car tonight and the fuel temp sensor checked out ok. After running a couple miles it was at 350 and I checked a couple more times over 5 minutes and it came up to 2400. I hadn't driven it in about a week and this time it had some hessitation upon acceleration until the engine warmed up. It still smells like it is runnung rich at start up and after warming up.

 

using Cosmic's data available above, the longer you run it the LESS resistance you should have....I would think after 5+ minutes of run time you should be in the 1200 ohm range.....check it again, it could still be the fuel temp sensor

 

IF the fuel rail temp sensor was reading 350 ohms at cold then it is a bad sensor. May be worth checking the battery in your multimeter and redoing the test... making sure you have the ohms scale on the meter set to the 20K setting... or 2 k if the rail is already warm.

 

Ran the car again and checked with two multi meters. Same results, I will try to explain better this time. I ran the car until the temp gauge was up to it's normal operating temp. I then parked it in the garage and checked the temp sensor a few times as the engine cooled off. The first reading was 348 then 770, 800, 1015, 1240, 1850, and the final reading I took was 2400 which was taken after the engine had cooled for approx. 5 minutes. Since The outside temp. is in the mid 70's I didn't keep checking after getting two readings in the 2400's in a row.

 

Ahhh the mid 70's on March 11th... gotta love that.

From the readings you took and the ambient temps I'd say your FTS is working perfectly....next.......

How about your other two ideas about ECT and Fuel pressure? Did you get to testing those components?

ECT should read-

about 300 ohms at 176*F
" 700 ohms at 130*F

****same scale as previous post for FTS

Have you had a chance to check the vacuum lines all around, especially the one between the plenum and the regulator? when the pump is energized (are you hearing the relay click in the passenger footwell as you switch the ignition to pos II... before engaging the starter?) you should have roughly 35psi under "normal operating conditions" at the rail.

 

Hello,

Did you ever resolve your warm start issue? Mine's doing the same thing, so I'd love to hear details from someone who's root caused this. My fuel temp sensor seems to be OK based on Cosmo's info... looking for some hints on what to look at next (ECT is 1st on my list). Many thanks,

Bob

 

Quick update... my ECT also checked out OK (300 ohms at operating temp). Ideas on what to check next are certainly welcome. Thanks again,

Bob