Backfire pops and vapor lock??

[chancho275]

I just flew down to San Diego (I live in Tri-Cities, WA) for an '88 Bronco. EB, 351 engine. The seller was an older man, and the thing is immaculate/clearly been taken care of. It was registered in Arizona to avoid California's emissions req. The seller did advise me that it would vapor lock on occasion when too hot, as well as the EGR valve was removed therefore rev while waiting at a light (put in N would neutralize that), and it also has a straight pipe with aftermarket cat. After testing it out and what not, I got it, deciding anything mechanical is fixable, but finding one in such pristine condition was a rarity. Well, now I'm here for the mechanical issues!

I drove it around OC a few days, and even took the longer scenic route back north along the 1/101! The thing was FINE. Only vapor locked a couple times, which would fire back up after a few minutes of cool down. But now that I'm home, Tuesday evening it started feeling sluggish upon acceleration, lunging, and even a few "firecracker pops" which I can FEEL with my left foot, so these pops might be coming from the bottom left (driver's POV). Spark plugs are brand new, and wires/dist. are good. Finally stalled through the neighborhood a couple times yesterday too.

Some buddies have suggested removing the cat altogether, and the thermostat as well (during summer) to aid in the vapor lock/cool down. Anyone here have a more accurate idea of what these "backfire pops" and sluggish acceleration/stalling might be?? As well as how to fix the vapor lock. Also heard FI motors don't get vapor locked, so I'm confused. Thanks in advance!

 

[Tiha]

Vapor lock is a term of disagreement, so no technically as we know it, it cannot vapor lock, BUT the fuel is moving through the rail slow enough that it does boil and not have any liquid for the injectors to inject.

It could very well be the cause of all of your problems. Running lean, means running hotter.

Caution on removing the thermostat. It will make the engine run hotter. Not at first, but when it warms up it never cools down. The thermostat slows the flow and allows the coolant in the radiator time to cool down, as much as it warms up the engine.
back in the old days we used to put washers in place of the thermostat to regulate the flow and keep engines from overheating.

Anyway.

Is this a two pump system? One on the frame rail and one in the tank?
I will assume yes.
In which case you have two options.
You can replace BOTH pumps, or you can flow test and try to figure out which pump is weak. It has to be a flow test. Pressure test tells you nothing.

Myself, I took option two.
Got tired of screwing with two pumps, put a single intank pump in. Never had another problem. Been doing this on F series and motorhomes for years.

In edit, if you want to verify if this is what's happening. Usually when the vehicle dies (from heat, vapor lock, whatever) You can cycle the key a few times and it should start right back up.
So key on ( do not crank) wait like 15 seconds.
key off.
Key on, wait 15 seconds
Key off.
Do this 5 or 6 times. It clears the boiling fuel from the rail. Brings cooler fuel from the tank.
It should start up if this is your problem.

 

[chancho275]

Vapor lock is a term of disagreement, so no technically as we know it, it cannot vapor lock, BUT the fuel is moving through the rail slow enough that it does boil and not have any liquid for the injectors to inject.

It could very well be the cause of all of your problems. Running lean, means running hotter.

Caution on removing the thermostat. It will make the engine run hotter. Not at first, but when it warms up it never cools down. The thermostat slows the flow and allows the coolant in the radiator time to cool down, as much as it warms up the engine.
back in the old days we used to put washers in place of the thermostat to regulate the flow and keep engines from overheating.

Anyway.

Is this a two pump system? One on the frame rail and one in the tank?
I will assume yes.
In which case you have two options.
You can replace BOTH pumps, or you can flow test and try to figure out which pump is weak. It has to be a flow test. Pressure test tells you nothing.

Myself, I took option two.
Got tired of screwing with two pumps, put a single intank pump in. Never had another problem. Been doing this on F series and motorhomes for years.

In edit, if you want to verify if this is what's happening. Usually when the vehicle dies (from heat, vapor lock, whatever) You can cycle the key a few times and it should start right back up.
So key on ( do not crank) wait like 15 seconds.
key off.
Key on, wait 15 seconds
Key off.
Do this 5 or 6 times. It clears the boiling fuel from the rail. Brings cooler fuel from the tank.
It should start up if this is your problem.

That's so good to know regarding the thermostat. I'm not mechanically inclined so was not aware of the ENTIRE tradeoff.
Also not certain of the pump system, but I'll check after work. Since it doesn't even wanna run smoothly now before popping and stalling, I'll have to change the fuel filter and research how to give it a flow test first. Maybe even replace the FPR, and another thread mentioned ICM as a potential culprit?

 

[Tiha]

ignition modules were common. Even the PIP inside the distributor.

 

[chancho275]

Vapor lock is a term of disagreement, so no technically as we know it, it cannot vapor lock, BUT the fuel is moving through the rail slow enough that it does boil and not have any liquid for the injectors to inject.

It could very well be the cause of all of your problems. Running lean, means running hotter.

Caution on removing the thermostat. It will make the engine run hotter. Not at first, but when it warms up it never cools down. The thermostat slows the flow and allows the coolant in the radiator time to cool down, as much as it warms up the engine.
back in the old days we used to put washers in place of the thermostat to regulate the flow and keep engines from overheating.

Anyway.

Is this a two pump system? One on the frame rail and one in the tank?
I will assume yes.
In which case you have two options.
You can replace BOTH pumps, or you can flow test and try to figure out which pump is weak. It has to be a flow test. Pressure test tells you nothing.

Myself, I took option two.
Got tired of screwing with two pumps, put a single intank pump in. Never had another problem. Been doing this on F series and motorhomes for years.

In edit, if you want to verify if this is what's happening. Usually when the vehicle dies (from heat, vapor lock, whatever) You can cycle the key a few times and it should start right back up.
So key on ( do not crank) wait like 15 seconds.
key off.
Key on, wait 15 seconds
Key off.
Do this 5 or 6 times. It clears the boiling fuel from the rail. Brings cooler fuel from the tank.
It should start up if this is your problem.

UPDATE: the pops were a backfire coming from the air filter!
And now it won't even start. It revs when I crank it, and I hear the 2nd pump buzz (the one on the frame).
Also, yesterday, the same pump stayed on/"buzzing" long after I stopped cranking it and pulled the keys out. Don't gotta be mechanically inclined to know that's not right, right?
Also the pressure tester gauge isn't even moving. After removal, there's definitely some pressure and fuel that comes out if I push it, but not enough to budge the gage I guess.

 

[chancho275]

Vapor lock is a term of disagreement, so no technically as we know it, it cannot vapor lock, BUT the fuel is moving through the rail slow enough that it does boil and not have any liquid for the injectors to inject.

It could very well be the cause of all of your problems. Running lean, means running hotter.

Caution on removing the thermostat. It will make the engine run hotter. Not at first, but when it warms up it never cools down. The thermostat slows the flow and allows the coolant in the radiator time to cool down, as much as it warms up the engine.
back in the old days we used to put washers in place of the thermostat to regulate the flow and keep engines from overheating.

Anyway.

Is this a two pump system? One on the frame rail and one in the tank?
I will assume yes.
In which case you have two options.
You can replace BOTH pumps, or you can flow test and try to figure out which pump is weak. It has to be a flow test. Pressure test tells you nothing.

Myself, I took option two.
Got tired of screwing with two pumps, put a single intank pump in. Never had another problem. Been doing this on F series and motorhomes for years.

In edit, if you want to verify if this is what's happening. Usually when the vehicle dies (from heat, vapor lock, whatever) You can cycle the key a few times and it should start right back up.
So key on ( do not crank) wait like 15 seconds.
key off.
Key on, wait 15 seconds
Key off.
Do this 5 or 6 times. It clears the boiling fuel from the rail. Brings cooler fuel from the tank.
It should start up if this is your problem.

In regards to option 2, going with one pump: is that a special order/aftermarket pump to replace both, or is it something I can find at the local O'Reilly's/AutoZone?

 

[Tiha]

Couple different ways to go about finding a single intank pump to use.

A stock ford pump is usually around 30 gallons per hour or 110 liters per hour.

I think I usually got one around 40 gallons per hour or 150 liters per hour or higher from some place like Jegs or summit. They list fuel pumps based on flow rating, but anything at at least 30gph should work.

At first I was soldering them to the pickup tube. Last few i have done I just hose clamped it to the pickup tube.

Going with a 95 bronco the pump comes in a module like this. But common sense says it should be enough to run your engine. But that will probably not fit through your filler neck.
https://shop.advanceautoparts.com/p...3-P?navigationPath=L1*14932|L2*14986|L3*15378

Just random, 92 chevy pickup with 454. I was using something that looked like this.
https://www.oreillyauto.com/detail/...duty-1992-chevrolet-c3500hd?q=fuel+pump&pos=0

Or

https://www.oreillyauto.com/detail/...duty-1992-chevrolet-c3500hd?q=fuel+pump&pos=4


Be sure to put a strainer on it.

 

[Motech]

Also, yesterday, the same pump stayed on/"buzzing" long after I stopped cranking it and pulled the keys out. Don't gotta be mechanically inclined to know that's not right, right?

No it's not, but Ford had that problem in their early EFI truck models. Fuel pump relay was not internally diode protected, and bi-directional current spikes served to weld the relay contacts shut. In brevity, pumps stayed running with key off.

Simple fix is replace the fuel pump relay. Get a Motorcraft unit, and you might as well do the EEC Power Relay (aka Main Relay) while you're at it. The live together.

Here's Ford's TSB text on this issue:

90ford25​

^ NO START - 1.9L, 2.3L, 3.0L, 3.8L, 4.9L, 5.0L, 5.8L, 7.5L - LOW STATE OF BATTERY CHARGE​

^ BATTERY - DISCHARGED - 1.9L, 2.3L, 3.0L, 3.8L, 4.9L, 5.0L, 5.8L, 7.5L​

^ FUEL PUMP - NOISY - 1.9L, 2.3L, 3.0L, 3.8L, 4.9L, 5.0L, 5.8L, 7.5L​

^ NOISE - "BUZZING" OR "HUMMING" FROM FUEL PUMP AFTER ENGINE IS TURNED OFFArticle No. 90-18-3​

​

FORD: 1983-90 CROWN VICTORIA, ******, EXP, MUSTANG, TEMPO, THUNDERBIRD 1986 LTD 1986-90 TAURUS​

LINCOLN-MERCURY: 1983-87 LYNX​

1983-90 CONTINENTAL, COUGAR, GRAND MARQUIS, MARK VII, TOPAZ, TOWN CAR 1985-86 CAPRI, MARQUIS 1986-90 SABLE​

LIGHT TRUCK: 1983-90 BRONCO II, BRONCO, ECONOLINE, F-150, F-250, F-350, RANGER 1988-90 F SUPER DUTY ​

​

ISSUE: ​

A "buzzing" or "humming" noise from the fuel pump may occur after the engine has been shut off. There may also be a no start condition or a discharged battery. These conditions are caused by a sticking fuel pump relay.​

​

ACTION: Install a new fuel pump relay. Refer to the following procedure for service details.​

​

1. Check the fuel pump relay circuit for proper operation. Refer to the appropriate EVTM for troubleshooting details.​

2. Install a new fuel pump relay, if the old one is defective.​

3. Check the vehicle for proper operation.​

​

PART NUMBER PART NAME​

​

F19Z-9345-A Fuel Pump Relay Assy.​

OTHER APPLICABLE ARTICLES: None​

WARRANTY STATUS: Eligible Under Basic Warranty Coverage​

OPERATION DESCRIPTION TIME​

901803A 1985-86 LTD/Marquis 0.6 Hr.​

(includes pinpoint test)​

901803A 1990 Town Car (includes 0.4 Hr.​

pinpoint test)​

901803A All Other Cars (includes 0.5 Hr.​

pinpoint test)​

901803A All Trucks (includes pinpoint0.5 Hr.​

test)​

These early fuel tank switches nd valves on dual tank setups also had problems The switches would short internally to power and effectively run both pumps. This could compound the other problems they had with the switching valves failing and pumping contents of one tank into the other while your engine runs, sometimes to the point of overflow out your filler neck!
Only on factory dual-tank setups though.

Also heard FI motors don't get vapor locked, so I'm confused.

You are right again; can't happen with EFI in traditional manner, as others here have already alluded.

(I've seen rare cases of fuel boiling in the rail--basically vapor lock--here in our warm climate when Costco dropped the ball and sold Midwest winter blends, but only a couple specific Honda models would actually "lock" and not start, and even that was not consistent. What was consistent is lean running symptoms and codes)

There is a different kind of lock these same early EFI Ford trucks suffered, and that was Hydro Lock. Ruptured fuel pressure regulator diaphragms would leak fuel into the control side, where manifold vacuum is applied. It could (and did!) got bad enough that fuel would flood into the intake and get drawn into a LH rear cylinder(s) nearest the FPR vacuum port. Cylinders would fill with fuel and cause real serious, fatal engine damage when fired back up.

Here is a cutout of the FPR, located front driver side mounted onto injector rail with a red vacuum hose attached to top ******.



This failure came on gradually, starting out with random, rich running conditions that would progress and include raw fuel ofors under hood and out tailpipe.

If you suspect this, the first whiff of raw fuel, shut it down, pull the FPR vacuum hose and inspect for raw fuel in hose and FPR vacuum port. If present, DO NOT DRIVE IT! Replace that regulator right away.



Most common cause of your reported symptoms are not fuel though. Well, not directly anyway. They are, in my experience:

• Green fuzz resistance in the PCM ground ground connector that pigtails off the battery negative. You can actually wiggle and tweak the connector while idling, and if bad, you'll hear your engine sputter, or even run nicer (round barrel connector below)
• Faulty Profile Ignition Pickup, or PIP sensor. That's the ignition trigger inside the distributor (this can be verified if you disconnect the SPOUT connector--the ignition timing bypass plug comes off your distributor--and the engine runs better)
• Squishy vacuum hose to Manifold Absolute Pressure Sensor (MAP) They get old, **** shut and wreak havoc with your fuel delivery when the computer calculates your driving at 19,000' altitude and delivers just enough fuel to cause your engine to buck, pop, fart and die.

This is your MAP sensor. Make sure vacuum pipe and rubber hoses are in goof shape, not squishy or pourous/cracked or otherwise leaking vacuum.




Good luck brah, and welcome to the playground!

 

[chancho275]

Jesus H. Christ. After replacing the relay, regulator, and in-line pump, I finally dove into the last potential culprit today (in-tank) only to realize, although the issue was from there, the pump itself was fine. The hose had gotten loose until eventually falling off altogether and that was that
I'll tell myself all the other replacements would've been necessary soon enough
But I guess that's how you learn. And damn did I learn a lot! Tips and advice here, as well as first hands-on experience on the Bronco. Can't thank you all enough for the knowledge drops!

 

[Wrench67]

If the hose was off wasn’t there fuel coming out and fuel going to the ground

 

[Blueblooded]

I just flew down to San Diego (I live in Tri-Cities, WA) for an '88 Bronco. EB, 351 engine. The seller was an older man, and the thing is immaculate/clearly been taken care of. It was registered in Arizona to avoid California's emissions req. The seller did advise me that it would vapor lock on occasion when too hot, as well as the EGR valve was removed therefore rev while waiting at a light (put in N would neutralize that), and it also has a straight pipe with aftermarket cat. After testing it out and what not, I got it, deciding anything mechanical is fixable, but finding one in such pristine condition was a rarity. Well, now I'm here for the mechanical issues!

I drove it around OC a few days, and even took the longer scenic route back north along the 1/101! The thing was FINE. Only vapor locked a couple times, which would fire back up after a few minutes of cool down. But now that I'm home, Tuesday evening it started feeling sluggish upon acceleration, lunging, and even a few "firecracker pops" which I can FEEL with my left foot, so these pops might be coming from the bottom left (driver's POV). Spark plugs are brand new, and wires/dist. are good. Finally stalled through the neighborhood a couple times yesterday too.

Some buddies have suggested removing the cat altogether, and the thermostat as well (during summer) to aid in the vapor lock/cool down. Anyone here have a more accurate idea of what these "backfire pops" and sluggish acceleration/stalling might be?? As well as how to fix the vapor lock. Also heard FI motors don't get vapor locked, so I'm confused. Thanks in advance!

 

[Blueblooded]

i tend to agree with the fuel pump option listed I live in southern New Mexico and it is very hot. I have a 87 EFI with a 185 thermostat and it never gets Hot even when towing a trailer. I would Also Recomend flushing the cooling system to include Radiator . Make sure they are clean and flowing between these two this should solve your problem good luck.