How many cranks to start up your MJ/XJ?

[hgeranium]

I wanted to get a little survey on how long it takes to turn your XJ/MJ over when cold and warmed up. My MJ has consistently taken 7 to 10 cranks cold, and 5-8 when warmed up. This is the oldest vehicle that I've owned (2nd oldest is a 94 GMC C1500), so I'm curious if it's just a 4.0 being a 4.0. It's not like the truck has trouble starting up, just more cranks than I would be expecting. I feel like I've seen online people starting up their XJs with 3-5 cranks.

 

My GMC always started up quickly, but I suspect the TBI played a part in it. My only in-person friend with an XJ has a chevy 3.4 swap, so I don't have any IRL comparisons to make.

[89 MJ]

Renix era Jeeps take longer to start. All three of my Renix MJs took longer to start than any of the GM TBIs I’ve been around. 

[hgeranium]

7 minutes ago, 89 MJ said:

Renix era Jeeps take longer to start. All three of my Renix MJs took longer to start than any of the GM TBIs I’ve been around. 

Great to know! It makes me feel better knowing it's a 'quirk' of the renixes rather than something I need to diagnose. Thank you

[AnotherOldJeepGuy]

49 minutes ago, 89 MJ said:

Renix era Jeeps take longer to start. All three of my Renix MJs took longer to start than any of the GM TBIs I’ve been around. 

Mine too.  I've heard this is normal multiple times, but I don't know that I ever heard anyone explain why?  So, can anyone explain why this is?

[89 MJ]

29 minutes ago, AnotherOldJeepGuy said:

Mine too.  I've heard this is normal multiple times, but I don't know that I ever heard anyone explain why?  So, can anyone explain why this is?

IF I recall correctly (that’s a big if) it’s because the computer doesn't remember which cylinder is supposed to fire next after being shut off, so it needs to turn over for a while so it can determine which cylinder to fire. 

[hgeranium]

36 minutes ago, 89 MJ said:

IF I recall correctly (that’s a big if) it’s because the computer doesn't remember which cylinder is supposed to fire next after being shut off, so it needs to turn over for a while so it can determine which cylinder to fire. 

After some independent research I did see something about slower logic from the ECU means it takes longer to verify crank position, so I'm sure you're right.

[watchamakalit]

I tell people it's a design feature that allows the motor to build oil pressure before firing. You know, race car stuff. 

[AnotherOldJeepGuy]

Never considered racing my Jeep, but good to know it is properly prepared to do so! 

[87MJTIM]

I have thought of the Renix ECU like Frosty the Snowman.  Each time Frosty puts on the magic hat, he wakes up like Rip vanWinkle, not sure where he is.

 

[pizzaman09]

It's definitely typical, both Renix MJs I have had take a few cranks.  Interestingly, my 09 Honda also cranks a few revolutions before firing, quite like the Renix system.

[DesertRat1991]

Priming the fuel system helps. My MJ might sit for a week or more. Before a cold start I'll turn the key to position 2 then off again a few times. You'll hear the fuel pump spin up each time.  Then, turn the key all the way and she starts right up.

 

She'll start just fine without doing this but it does crank longer.

 

[AnotherOldJeepGuy]

Interesting stuff!

[watchamakalit]

On 9/24/2025 at 12:33 PM, DesertRat1991 said:

Priming the fuel system helps. My MJ might sit for a week or more. Before a cold start I'll turn the key to position 2 then off again a few times. You'll hear the fuel pump spin up each time.  Then, turn the key all the way and she starts right up.

 

She'll start just fine without doing this but it does crank longer.

 

I have tried this trick with mine. Didn't help. I think it's just normal race car things. 😂

[89 MJ]

3 minutes ago, watchamakalit said:

I have tried this trick with mine. Didn't help. I think it's just normal race car things. 😂

Same experience first. My truck would need to sit pretty much all winter for me to need to prime the fuel system. And I've never seen a fast starting race car either...

[watchamakalit]

1 minute ago, 89 MJ said:

Same experience first. My truck would need to sit pretty much all winter for me to need to prime the fuel system. And I've never seen a fast starting race car either...

We all know MJ's are pretty much race cars from the factory any way.....

[89 MJ]

3 minutes ago, watchamakalit said:

We all know MJ's are pretty much race cars from the factory any way.....

They were such a high performance racing vehicle that the 4.0 would've been too fast for the SCCA racing, so they had to use the 2.5L instead. Or at least that's my story and I'm sticking to it

[watchamakalit]

1 minute ago, 89 MJ said:

They were such a high performance racing vehicle that the 4.0 would've been too fast for the SCCA racing, so they had to use the 2.5L instead. Or at least that's my story and I'm sticking to it

[Eagle_SX4]

4 hours ago, watchamakalit said:

We all know MJ's are pretty much race cars from the factory any way.....

There was a land speed record set with a 4.0 liter Comanche in 1987. The record only stood for 2 years.