Hard to start when warm...

[88MJay]

My MJ starts as soon as you hit the key when it is cold. But, when it's warm or been driven for a while it is tough to re-start. I usually have to crank it for about 3 seconds... turn the key back... crank again for 3 seconds and then it slowly catches and runs. Sometimes it revs above 2000 rpms or so when it finally starts and then comes back down to idle. Other than this it runs fine.

 

Anyone ever have this issue or know of anyone who has? And if so... what is the fix for it?

[JeepcoMJ]

yea, mass airflow sensor would be my guess...it's a sensor problem for sure tho in my experience. throttle position sensor too it could be, or even a faulty CPS

[88MJay]

I think it's probably a sensor too but I don't want to just start replacing stuff until I nail down the culprit. Hopefully someone else has had this same thing occur and figured out exactly what it was.

[JeepcoMJ]

well if you can get a flow chart for the sensors, you can use a voltmeter (or whatever that thing is called) to measure the power flow through the sensor...and know if it's wrong or right.

[HOrnbrod]

Here's a good link that describes testing the various Renix engine sensors:

 

http://tinyurl.com/2md8a5

[87manche]

yea, mass airflow sensor would be my guess...it's a sensor problem for sure tho in my experience. throttle position sensor too it could be, or even a faulty CPS

No MAF, uses a MAP sensor.

 

anyway, my 2 cents.

Heat soked component somewhere, could be a sensor, could be the ignition module itself.

Warm it up, pull a spark plug wire and check for spark.

if it's got spark then the ignition side is good, move on to fuel pressure.

[Eagle]

yea, mass airflow sensor would be my guess...it's a sensor problem for sure tho in my experience. throttle position sensor too it could be, or even a faulty CPS

No MAF, uses a MAP sensor.

 

anyway, my 2 cents.

Heat soked component somewhere, could be a sensor, could be the ignition module itself.

Warm it up, pull a spark plug wire and check for spark.

if it's got spark then the ignition side is good, move on to fuel pressure.

Yep. Could be a sensor, but coils usually fail first when hot. In the Renix system, the coil is part of the ignition module assembly. I would not overlook that possibility. Many years ago I replaced a carburetor and then a distributor when the only real problem was a faulty condenser (which was new, so I never thought to check it).

[4play]

a slight threadjack, but possibly related...

 

My '87 (auto tranny) always takes two attempts to start. Hot or cold, doesn't matter. If it does, by some freak chance, start on the first try, it will die when you put it in gear. I also sometimes get the high rev when it first starts.

[JeepcoMJ]

a slight threadjack, but possibly related...

 

My '87 (auto tranny) always takes two attempts to start. Hot or cold, doesn't matter. If it does, by some freak chance, start on the first try, it will die when you put it in gear. I also sometimes get the high rev when it first starts.

 

my thoughts are CPS if it won't start right away. I just replaced the flex-plate on my 87 sport truck because it was cracked and wobbling...the truck was running like $#!& and clanking up a storm (knew it wasn't engine knock as it was from the bellhousing). with the new flex-plate, the CPS is now getting a correct reading hence it starts faster, starts on the first try, and runs like a top. now to do the exhaust manifold...

[88MJay]

I've never swapped a CPS. Is it as hard as everyone makes it out to be? How much are they and what brand/place should I get one?

 

I've got a friend down the road who has a ton of Renix stuff. Maybe I can get a coil to try as well.

 

Thanks everybody. :cheers: