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Fuel pressure loss, bad gas mileage, leaky injector?


Dr.Gonzo

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Hi all,

I have 1988 Bronco II XL 2.9l 2WD with Auto trans. Car has 250.000 km (155.000 mi) I bought it 3 years ago. I'm a metric guy but I'll try to use both systems in my posts to make things easier for everyone.
My B2 is a daily driver, city mostly with a bit of highway combined. My mileage is pretty terrible lately. 22l /100km (10 mpg). It was around 15l/100km (15mpg) before these issues started and I was ok with that. I know it can do even better than that but if I can get it back to 15 I'll be happy. I think it should be 17mpg in the city when the car is brand new. The best I got out of it was 10l/100km (23mpg) on the highway last year.

I did a lot of reading on the forums and I know that this is another fuel issue/bad gas mileage thread but I figured repeating and talking about it again can't be bad thing. I wanted to share my problem to help others as well.

What I did so far :

Made the jumper cable and pulled out the codes. I'm not sure if I got it right but I think I got 11 (System OK). It's either that or 22 cause I'm not sure about the pause in between the flashes. If the system repeats the codes twice then it is 11.
Got the same codes for KOEO and KOER.

I can hear both pumps priming when I turn the key. Bought the fuel pressure tester and took the readings. I have 30 psi in the system with engine running (Should this be 40?). When I turn the engine off pressure starts to drop right away. Not rapidly to zero but in less then 2 min drops to 10 psi. I didn't wait to see how fast it will get to 0 cause this was enough for me. There must be a leak in the system.

Inspected fuel lines from the engine all the way back to the tank, no visual leaks, looks dry. All the connections on the tank, canister filter, hi pressure pump, inline filter, all the way up to FPR look ok.
Pulled the vacuum hose of the FPR, no leaks. I can smell gas a bit but it is dry. I'm not sure if this is my main problem.
Wanted to pinch the lines to diagnose further but looks like i have plastic hoses coming to the FPR so I gave up on that idea for now until I figure out how to do it.

I have new FPR and O2 sensor on the way. Decided to replace FPR anyway cause it looks like it has been there from day one. I'm not sure if I should touch O2 at all but it can't hurt changing it, I guess...

I've red that a bad check valve on the low pressure pump can cause pressure loss but I'm not sure if that can be related to my problem.

Is there a possibility that I have a leaky injector?
I have to change valve cover gaskets soon, so I was thinking of pulling the injectors out and clean them anyway.
Is there a way to determine if the injector is cracked?
Engine is dirty and oily in that area cause of the gaskets. Can all that oil mess up the injectors in some way and cause leaks on them?

I replaced fuel filter less than a year ago. Will change it when I get FPR. Last year I did spark plugs, cables, cap and rotor. Changed PCV valve and grommet 6 months ago. Idle control valve has been cleaned at that same time. I have new air filter in. Vacuum Hoses and PCV hose looks good but I might change them all in near future. At least I will know when it was done.

Car starts great cold, a bit of hesitation when it is warm but now I can address that to loss of pressure? Idle is ok, sputters a bit but it doesn't look or sound really bad. Runs fine to me.

Is there anything else I should check? Any thoughts? What would you do?


Thank you for your time!
 
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Dr.Gonzo

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So... It was faulty fuel pressure tester. Just to be sure I tried it on different car and it was doing the same thing. I managed to get steady 30psi KOEO and 32 KOER on the Bronco only once and after that it started acting up again. Pressure drops quickly. Sent it back, will get new one today and I'll try again.

In the meantime I did an oil change, replaced FPR and vacuum hose on it. Put new O2 sensor in. Taking that O2 out was PITA but i managed to do it. Pipe wrench rules :D. Had to put loads of penetrating oil and at the end to torch it.

Car runs smoother now, idle is better and accelerates better. Will see how it goes. I just hope this fixes it. It sucks when your daily driver is spitting gas like mad.



Cheers
 

RonD

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Just for future test, all fuel injection computers have a "Clear Flooded Engine" routine
You can use this to test if fuel is leaking into intake.

Key on
Press gas pedal to the floor and hold it down all the way
Turn key to START

Engine should turn over but NOT start or even fire a little.

With key on the computer is running, when you press gas pedal to the floor the TPS(throttle position sensor) sends computer over 4.5volts, when computer sees this it checks RPMs, if RPMs are 0 then computer will shut off fuel injectors but leave spark on, this is "Clear Flooded Engine" routine.

So when engine turns over there is spark but no fuel, no start, if it fires then fuel is leaking in, could be from a leaking injector, or leaking FPR via vacuum hose.
If it fires you can repeat the test but unplug the coil, so no spark, then crank the engine a few times and pull the spark plugs, the wet spark plug has the leaking injector.
 

Dr.Gonzo

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Thank you RonD!

Some great tips there. I will try that and post my results.
 

Dr.Gonzo

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My new tester arrived yesterday. Key on, pressure slowly rises to 27 Psi. With engine running system is holding pressure at 27 Psi. With engine off it slowly rises over 30Psi (at least it doesn't drop). I red somewhere that this rising pressure is normal.
When I start the car again it drops back to 27Psi where it holds steady. On throttle snap it goes up around 5Psi, drops slightly below 27 and it gets back there. With vacuum hose unplugged from the FPR It goes up to 37Psi. Hose back in, back to steady 27Psi. All in all It is a bit low I guess, looks like the booster pump is weak (explains a bit longer cranking time). Not sure if weak booster pump can cause bad gas mileage?
FPR is new and fuel filter is new.

Just for future test, all fuel injection computers have a "Clear Flooded Engine" routine
You can use this to test if fuel is leaking into intake.

Key on
Press gas pedal to the floor and hold it down all the way
Turn key to START

Engine should turn over but NOT start or even fire a little.
I tried "Clear Flooded engine" routine. Car turned over few times and started. So in ideal conditions it should not start at all? No matter how long I hold the key on?
I did tests on TPS as well, just to be sure I'm getting over 4.5V on WOT.
My reference voltage is 5V, throttle close voltage 0.98V, WOT voltage 4.61V so I guess I'm good there.
I still have to try "wet spark plug" test.

I did all of this yesterday, looks like today car runs and idles better or I might be imagining things. Maybe it takes some time for computer to learn that new O2 sensor is in.
Although I always reset and use odometer to calculate mileage i know that my fuel level I gauge is pretty accurate in top part of the tank (over 1/2). Today fuel level doesn't look promising and looks like it is still burning to much gas Hm...:icon_confused:
I guess I shouldn't rely on that and do the math after 200km or so.
 

RonD

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Yes, TPS above 4.5volts at 0 RPM should turn off fuel injector pulses.
Shouldn't start until you release gas pedal.

Could be you need to do the throttle cable mod.
Throttle cable stretches over time, so when you press down on the gas pedal you get 7/8 throttle, not WOT(8/8).
When testing TPS you probably opened throttle by hand, not gas pedal, so......................

Throttle cable mod is putting wire ties, zap straps, on the end of the cable where it connects to gas pedal, this takes out the slack and gives you back WOT.

You should be fine at 27psi fuel pressure.

And if it isn't dropping after 5 minutes or so, engine off, then no leaks.

Yes, new O2 sensors change the computers Long Term Fuel Trims, so takes about 5 to 10 drive cycles for computer to adjust those.
1 Drive cycle is a warm up to operating temp and then cool down to outside temp
 
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Dr.Gonzo

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Could be you need to do the throttle cable mod.
Throttle cable stretches over time, so when you press down on the gas pedal you get 7/8 throttle, not WOT(8/8).
When testing TPS you probably opened throttle by hand, not gas pedal, so......................

Throttle cable mod is putting wire ties, zap straps, on the end of the cable where it connects to gas pedal, this takes out the slack and gives you back WOT.
Ok I just did this... WOW, and I thought my car was running fine...
What a difference with this mod! Runs awesome now! Like a brand new truck :icon_bounceblue:
Didn't tell my wife and asked her to drive today. That was funny moment :"What did you do to this car?!" :D

That thing had 1" slack, crazy... I had to put 4 zap straps. I was careful not to over tighten the cable, left just a little bit of slack. I will probably try to put something else, I don't like 4 zap straps stacked like that but it works great for now.
I did "Flooded engine routine" test after cable mod and it started again. Different though, a bit longer crank but engine started with less rpm kind of... I don't know how to explain this.

Discovered few "new" things while working on cable. My throttle body needs cleaning... and my kick down cable was not sitting properly in the firewall. Did re calibration on it and put it back in place. I'm not sure if it was combination of things but it downshifts better now and hard kick when it shifts from 1st to 2nd is less pronounced now. I might need new vacuum modulator to fix this but so far so good.

You should be fine at 27psi fuel pressure.

And if it isn't dropping after 5 minutes or so, engine off, then no leaks.
Yes, it is holding. Over 5 min for sure. I will do it again and let it sit for a while.

Yes, new O2 sensors change the computers Long Term Fuel Trims, so takes about 5 to 10 drive cycles for computer to adjust those.
1 Drive cycle is a warm up to operating temp and then cool down to outside temp
Good info, I have so many things to learn!
Your help is much appreciated, thank you very much sir! :beer:
 

RonD

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Good work on the throttle cable mod :icon_thumby:

Yes, since it happens so slowly you don't notice lack of WOT.

Not sure on the Clear Flooded engine, you could try putting a weight on gas pedal so it is at WOT, then test TPS to see if it is over 4.5volts and stable.

But if it doesn't fire right away and fuel pressure holds after engine is off then I would rule out leaky injector or leak into fuel pressure regulator vacuum hose.
 

Dr.Gonzo

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Been busy lately so I haven't done much to figure it out. Still no good news... After 250km (156mi) still bad. 10mpg... Long fuel trims should have been adjusted by now. I've checked all my vacuum lines with propane, didn't find any leaks. I've tested coolant temperature sensor and it is working fine. I have 4.6V ref. voltage, on cold engine sensor has 27KOhm, on warm engine reads 3.5KOhm.

I have to start checking my signal and ground wiring...
 

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Pull out a couple of spark plugs, see if engine is actually running Rich, at 10mpg it should be.
If they look OK you have a gas leak, and not thru the engine.
 

Dr.Gonzo

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Was busy moving... I wish I have more time to work on the car...

I pulled out 2,3,4,5 real quick. All look normal except No 3. It was a bit wet and it was under torqued. It had visible leak around the spark plug when the engine is running. I could see it cause of all that oil on the engine, looked like air bubbles coming out combined with unburned gas... I tighten it a smidgen and leak stopped. I wish I have torque wrench that goes under 20lb so I can torque all of them properly.
I'm not sure if that under torqued No3 was the culprit but looks like I have a miss fire on it. It wasn't soaked but it was wet. I have to check distributor cap and rotor. I replaced it a year ago though together with spark plugs and cables so everything it is fairly new...
I must power-wash engine bay as well and remove all that gunk oil so I can see better what is going on in there.
My first thought when I saw No3 wet was that injector is stuck open. I have double checked all the injectors with mechanic's stethoscope (nice that we have one at work) and did the sound test on them again. They are all ticking with same time intervals and make the same sound. So I guess they are ok.
If there is a leak it must be on the engine side somewhere. Fuel lines are dry as a bone from FPR side all the way to the tank. I will double check fuel pressure just to make sure everything is ok.

Thank you for all your help Ron.
 

Dr.Gonzo

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Update :
So last time I actually checked 2,3,5,6 as they are the most accessible ones.

After pulling all the plugs out I discovered bad connection on spark plug No4. Cable was not plugged in properly and connector was bent. It was barely touching top of the spark plug causing missfire... I can't believe how sloppy I was when I did tune up... Spark plug was awful. After inspecting them all I decided to put new set in. Cleaning them and re-gaping them was not worth it. Replaced copper Champion with NGK platinum.
Fixed loose cable connector on No3, pinched it a bit to sit nicely and put everything back together.
250km(156mi) later I was getting around 14mpg combined. 80/20% city/highway. Still not the best I can get out of it, but way better than 10mpg...

Today I inspected and cleaned contacts on distributor cap and rotor. Noticed that some of the contacts are slightly worn out. I will definitely replace both, cap and rotor with something better as I went with the cheapest option at the time. Car runs better and idle is smoother after cleaning. I double checked timing, 10 degrees spot on.
Might go with new in-tank pump assembly at some point. Pressure is below specs, cranking time is still longer and I definitely want working sending unit.
Next thing I must do is to replace valve cover gaskets... Planning to clean injectors and replace basket filters and O-rings while in there.

Will post an update when I get my gas mileage back to where it was.
One thing I've learned... Even if it doesn't make sense, always start with checking the basics first...
 

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