Cranking Time Oddity?

[robfg67]

I have a '90 Renix era MJ with the 4.0.

 

I always let the pump prime for a few seconds before I start the engine and it always take several cranks to get her started. 

 

This is true when the engine is either cold or up to normal operating temperature. Makes no difference.

 

However, I left her parked outside (the garage) the last two days in the 85 degree heat & sun and both times I started her, the engine started on the first crank.

 

Can anyone explain why? 

[pizzaman09]

You know what's funny, my 90 4.0L did the exact same thing the other day.  It always takes a couple of seconds of cranking to start except for yesterday afternoon when I went to leave work, it fired off immediately.

[89 MJ]

I’ve noticed this about my 89 too. I used to always let the fuel pump cycle. I didn’t wait once for some reason and it started much quicker. Doesn’t matter if it sits overnight, if it’s a hot restart, or if it sat in the sun for a few hours. Couldn’t tell you why though. 

[robfg67]

It's a sweet mystery of life.

[Ωhm]

On 6/12/2025 at 7:48 PM, robfg67 said:

I always let the pump prime for a few seconds before I start the engine and it always take several cranks to get her started.

21 hours ago, 89 MJ said:

I used to always let the fuel pump cycle. I didn’t wait once for some reason and it started much quicker

 

Pump prime is a two-fold process.

1. Allow fuel pump to run for 2-3 seconds.
2. Check valve to prevent fuel drain-back through the fuel pump to the tank when fuel pump is OFF.

Question is ‘Does fuel pressure drop once the pump is turned OFF?’ Faulty check valve.

 

I’m not saying this is your cranking issues, but it sure could help here.