M38A1 F-head Fuel Pump/Vacuum System vs. CJ3-B and others

LeeG · Post by **LeeG** » Mon May 01, 2006 1:54 pm

This topic is also to pertain only to the 4cyl F-head motor.

Why is it that the M38A1 has the vacuum line setup connection with the PCV valve, head, and distributor and not all F-head motors are setup this way? They are all still the same motor.

Lee
53 M38A1 F-head

OKCM38CDN · Post by **OKCM38CDN** » Mon May 01, 2006 3:16 pm

M38A1 was set up for water proof operation, possible fording...

LeeG · Post by **LeeG** » Mon May 01, 2006 4:59 pm

I remember Wes talking about the vacuum system for the transmission a while back. How it was basically used for ventilation during fording.

But is it the same case for the motor? You know, the small vacuum hole under the carb, the one to the distributor and the lines to the fuel pump and PCV valve.

Lee

OKCM38CDN · Post by **OKCM38CDN** » Mon May 01, 2006 5:20 pm

What the underwater system does is pressurize the block, bellhousing, transmission and Transfer case to help keep the water out.

The lines to the distributor do this and also keep air flow thru it to help keep ithe coil cool...

The line to the carb vent is just that a vent, but water proof... vented to the carb intake...

Hope this helps...

LeeG · Post by **LeeG** » Mon May 01, 2006 6:58 pm

So things like the plug in the side of the head under the carb is ok to stay plugged and will it be ok if I go with the glass top fuel pump that comes off a 3B because it should bolt up the same and supply th esame amount of fuel, it just doesn't have the vacuum system?

Lee

OKCM38CDN · Post by **OKCM38CDN** » Mon May 01, 2006 7:33 pm

I believe so, I am not familiar with the CJ3... I have heard there is a different space or no spacer used with the civilian fuel pump... maybe someone else can verify that...

Cacti_Ken · Post by **Cacti_Ken** » Mon May 01, 2006 7:58 pm

My M38 with the L head motor had a glass bowl fuel pump on it. No vacuum. It didn't use a spacer.

LeeG · Post by **LeeG** » Mon May 01, 2006 8:01 pm

Can you post some pics or just explain what you did with the PCV valve and the other components on the engine that were tied to the vacuum?

Then again, that's an L-Head and I am not familiar with the differences.

Thanks,
Lee

Post by **wesk** » Wed May 03, 2006 11:10 am

Whatever fuel pump you use make sure you use the gasket/spacer setup designed for that fuel pump installation. Otherwise you may end up with incorrect pressure.

LeeG · Post by **LeeG** » Wed May 03, 2006 12:10 pm

I think I've decided to go original with the pump and pay the $160 that John at MidwestMil wants.

The glass top one looked cool and was a whole lot cheaper which made it something to think about but I didn't know what other problems I would create. Especially with the whole vacuum setup across the engine. Which I'm not sure I totally understand it all. I've been spending a lot of time reading the manuals and hopefully through that and forums and asking dumb questions, I'll get it all figured out.

Thanks,
Lee

GIJOE290 · Post by **GIJOE290** » Wed May 03, 2006 4:24 pm

LeeG wrote: ...asking dumb questions, I'll get it all figured out.
Thanks, Lee

Lee, There are no dumb questions, esp if your not familure with your drivetrain & jeep. Now, NOT asking for help if/when you need it, is dumb; and sometimes costly.

My advice is keep asking!

We all learn from the posts. I'm not even working on my A1 and I learned something from your post & replys. If you think something might have been asked before, you can try using the search features to seek the answers.

Good luck on your project!

David

Post by **Ryan_Miller** » Fri May 05, 2006 7:41 am

There is a fording document over in the downloads section under M38 that is very good. It should help clear some stuff up about the pressurization and routing of the vacuum lines.

Good Luck!