TBI Vapor Lock possible?

[3upadventures]

Hey guys,

So I bought my '77 Cherokee back in January and have been driving it around with mostly no problems. My ex experienced what we think were some vapor lock issues when he drove it over from Denver but he re-routed some of the lines and the issue didn't resurface during a few trips to Telluride (~40 mi each way) or to Grand Junction (~80 miles each way)

About a week or so ago, I drove over to Telluride in the middle of the day. It ran great until I was almost there and it started sputtering and wanting to die going up the hill. I pulled over and it died as I slowed down. I waited about 15 minutes and with just a little touch on the accelerator as I restarted it took off and drove the last 5 miles to town just fine. I walked around town for a few hours and drove home after dark with no issues. I didn't really think about it being warm outside but it *was* one of our first real spring like days.

Yesterday, I was coming back from Grand Junction with thermometers all along the way saying 75-78 degrees. It's been a warm winter but the warmth still felt amazing! The jeep didn't really seem to enjoy it however, and about a half hour out of Junction started cutting out and dying. I pulled over, let it cool for 20 minutes and cruised south again. The cycle repeated itself a few times until I stopped for about an hour in Montrose killing time in a few stores and drove the final 20 miles home in the cool after-dark hours with no issues at all.

The jeep has a junkyard TBI conversion (build thread for the jeep). Is it possible that the cutting out is vapor lock even *with* fuel injection? Is there something else that would cause the motor to seem completely fuel starved and restart without anything more than a 15-30 minute cool down?

[fulsizjeep]

TBI systems can vaporlock, yes. Is there a phoenolic (plastic) spacer between the TBI and intake? You could also have issues with the fuel pump. It may be making adequate pressure but is it making adequate volume? I had this specific problem the last time I was vapor locking a carbed 401.

[Stuka]

Vapor lock is certainly possible. I think it would check the fuel pump. Its possible its pressure is lower than it should be, which would allow the fuel to boil easier (higher pressure = higher boiling point).

Its also possible the the pump itself may be getting hot, and then not putting out enough fuel or maybe even stopping all together.

[AwesomeJ10]

Yes, TBI can vapor lock, but it's pretty rare in a properly working system and should not be considered normal. The reason why is TBI has a higher pressure (10-15psi) as opposed to carbs (3-5 psi)

Check your fuel pressure while driving. You should be at a ROCK SOLID (with no movement) 10-15 PSI.

It's possible the fuel pump is going out, is constricted (fuel filter or too small of hose - 3/8") or that the TBI fuel pressure regulator (located in the TBI itself) is going out.

[3upadventures]

Thanks so much for all the thoughts!

I'll get out and do some testing/investigation this weekend.

[REDONE]

I just read through sgtpolitenesseses whole thread, it looks like on the last page he was talking about the same thing before he sold it to you. Looks like what he did was clean out a clear glass pre filter between the tank and the pump because it was plugged up. He mentioned thinking about dropping the tank and cleaning it out too, but never said if he did or not. Looking for and checking that prefilter sounds like the quickest, easiest and most likely solution at this point!

[REDONE]

Did you get a chance to check that fuel filter over the weekend? Or where you too busy playing "Hunger Games" at Cabela's?

From sgtpoliteness' description it should look something like this:
http://www.pepboys.com/product/details/8566803/00468

And I think that if you crawl under the Cherk behind the drivers door and look up and back, it should be right there inside the frame. Not positive, but that's where it makes sense being between the tank and the electric fuel pump.

[Bill usn-1]

Found this statement in Jason's build thread.

Fuel pump is installed above the trans cross member (nice and safe!) and wired in.

If this is true then it is not installed according to any of the recommended FAQs on the binderplanet and not the way the factory did it.

Pumps push better then they pull and they should be away from heat.
So the pump should be mounted as close to the tank as possible and at or near the bottom level of the tank.
3/8" fuel line should be run all the way with as few connections as possible.
No brass fittings used.
best pump location is normally on the frame rail near the rear axle.
A 3/8" clear fuel filter should be used between the tank and pump.
Then use 3/8" universal steel brake line along the frame from the pump to the firewall. A short piece of 3/8" fuel injection rated hose can connect the line at each end.

Return line should be a straight piece of 5/16" line.
Proper installation can reduce or eliminate most vapor lock issues.

I have wheeled the 14ers many times with no issues.
Will be back there in July for another trip.

[SJTD]

I've got the Mopar MPI in my CJ. It quit on the freeway in not too hot conditions after about 1 hr. Restarted after 20 minutes. Second time I tried the same trip with a tow bar and a following truck it lasted about 2 hours.

Hesco's forum suggested a new filter which seems to have fixed it. Filter is before the pump on the crossmember in front of the tank.

[Bill usn-1]

The reason for running a clear filter before the pump is for an easy check of condition.
On the suction side there will be an air bubble at the top of the filter until the element starts to get restrictive. Then the level keeps rising until no bubble left. Then you know it's time to change the filter.

You don't need tech support or factory technicians to tell you when to change a fuel filter!
All filters should be checked at the same time.
Oil, fuel and air.

[SJTD]

Thanks.

It didn't behave like a plugged filter... you know stumble at high load, ok at low. The difference being that restriction upstream of the pump caused cavitation. Seems obvious now but not at the time.

[csuengr]

My CJ has brass fittings all over the place and no vapor lock issues. My supply line is also 5/16 feeding a LT1. Again, no issues. The only advantage 3/8 has over 5/16 is fittings are easier to find.

[csuengr]

Just thinking, but this random dying while hot also sounds like a bad or overheating ICM.

[Bill usn-1]

There's a lot of guys on the web that make repairs or perform installs that are not the way they should be.
Some work and some don't. Some work for a while and then a problem pops up later when you don't want it to, like up in the hills away from any help, middle of the summer when things are hot.
If a system is not installed similar to the way the factory did it then you may be setting yourself up for failure.
The last thing you need is for the engine to die or sputter off road or even pulling out into traffic.
The factory used 3/8 feed and 5/16 return lines. They also used fuel injection rated lines. No one should be recommending anything other than that to others.
If changes or short cuts are taken then that's a personal choice and should not be posted as a correct way to do it.
The object is to make the old vehicles more enjoyable and safe so we continue to drive them.

[Bill usn-1]

Just thinking, but this random dying while hot also sounds like a bad or overheating ICM.

Yes an over heating ignition module or coil is another possibility.
I have seen many ignition modules improperly mounted without a proper heat sink or proper thermal paste.

[will e]

If I was running TBI I would have a fuel pressure gauge in the cabin. It will tell you a lot.

[csuengr]

There's a lot of guys on the web that make repairs or perform installs that are not the way they should be.
Some work and some don't. Some work for a while and then a problem pops up later when you don't want it to, like up in the hills away from any help, middle of the summer when things are hot.
If a system is not installed similar to the way the factory did it then you may be setting yourself up for failure.
The last thing you need is for the engine to die or sputter off road or even pulling out into traffic.
The factory used 3/8 feed and 5/16 return lines. They also used fuel injection rated lines. No one should be recommending anything other than that to others.
If changes or short cuts are taken then that's a personal choice and should not be posted as a correct way to do it.
The object is to make the old vehicles more enjoyable and safe so we continue to drive them.

There is nothing wrong with brass fittings for fuel lines. Most of us don't have the $200-300 to do it the "correct" way. That and the "correct" way is usually dictated by those trying to sell you parts.

My 88' GW used 5/16" feed and 1/4" return, so does my CJ. My 77' Cherokee, which has a fuel system (tank, pump, complete fuel lines) from a 90' Bronco, uses 5/16" feed and 1/4" return.

My CJ has had no issues over the last four years using brass hose barbs, aluminum hard line, and fuel injection rubber lines. I am running 43 psi fuel pressure. Before that, it was 5 psi for the carbed 360, through the same fittings and hard lines.

There is nothing in the setup used for the fuel lines, that I can see, that should be causing vapor lock. The ICM mounted on the fender (flat ICM on rounded fender BTW) is probably not doing the ICM any good. The ICM needs a good heat sink and plenty of heat sink compound.

Other than a plugged fuel pickup, or plugged anything before the pump, the fuel system should be good.

[Bill usn-1]

Here's a couple little tips,
1. Brass fitting do affect the flow of fuel. The ID of each fitting is smaller than the ID of the line used.
2. A very cheap and simple fuel line can be made by simply heading down to the parts store where they have universal brake lines in sizes up to 1/2"ID and lengths up to about 6'.
The lines have double flares and nuts on each end so if needed flare fittings can be used. This maintains the correct ID thru the entire run. Simple rubber hose rated for injection and clamps made for injection hose on each end complete the connection.
The brake lines are about $5-10 and the fuel injection hose is about $1/ft. Far from $2-300.
I have been showing and helping guys install fuel injection for over 15yrs. I have seen every wrong/short cut type of installation you can imagine.
I have personally tested many to see if they actually work or not.
Just because someone may get by with a shortcut on their vehicle does not make it a recommended practice for everyone else. A guy that only installs 1 EFI system on his vehicle is NOT and expert in EFI installation.
If it's done correctly the first time then they won't have those issues.
Pressure and flow volume are 2 different things.
The pump should be mounted as close to the tank as possible and level or below the tank if possible.
I have had other argue with me that they mounted the pump in the engine compartment and had "no" problems. So it must be fine to tell everyone else to do it that way. It's not ok and should not be done.
I had guys loop the return right back to the inlet side of the pump line to avoid returning it to the tank. Then they tell everyone t works for them so just short cut it and it will be fine. It's not!
Did all these guys get away with the short cuts? Sure they did. Would they ever come back and admit if they later experienced a problem, no.
If a person followed their recommended short cuts and later totaled their truck because it vapor locked while off roading, what then?

You can short cut things like paint and body work.
But do not short cut stuff that can damage the vehicle or hurt someone.
Brakes, fuel systems, tires...etc
It's like wheeling with a guy that doesn't carry tools or a spare tire or is drinking on the trail.
Leave that guy in the camp, you don't need him.

[Tad]

Excellent post Bill, glad you onboard here to set things straight.

[jsinajeep]

Dam it Bill, short and true about short cuts. Thumb up to you.