1988 Ford Bronco 2 Hesitating, Backfiring, Loping Idle.

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Please fill out the following to ask a question.

Ford:
Bronco II:
1988
:
160,000: 2.9L EFI, V6, 4WD, 5-speed manual
:
Hesitation, irregular idle, occasional backfire, loss of power, sometimes gets whiff of gas in the passenger compartment and I'm told black smoke is coming from tailpipe.

The problem started out as just an occasional hesitation and has gotten progressively worse over time. It's been in 2 different repair shops with very good reputations and has been in one of them for the last week. They've diagnosed it as a case of demonic possession. Here's what's been tried so far, but not necessarily in order.
1. Drained water from the fuel pump along the rail.
2. Replaced Idle Air Control valve.
3. Changed to higher octane fuel or Ethanol-free fuel.
4. Tune-ups, including new plugs, wires, distributor cap, rotor, and wire separators to prevent interference between wires.
5. PCV valve changed.
6. MAP and O2 sensors changed.
7. Seafoam added to fuel per manufacturer's instructions about every 10 tanks of fuel.
8. Fuel injectors tested (no dirt).
9. Fuel injector cleaner added to fuel.
10. Oil, oil filter, air filter changed at regular intervals.
11. Engine compression is about 125 in all cylinders.
12. Probably some other stuff I've forgotten about.

If I didn't like the vehicle so much and need a 4WD for winter commuting, I'd have gotten rid of it before now. I got a second one (2WD) as a spare parts vehicle but it needs a transmission rebuild and I need to replace either the grounding wires and/or the starter solenoid.

So... the intermittent nature of the 4WD one has me stumped. A couple of times I got a code light but by the time I got a code reader and hooked it up, there was nothing to download. I couldn't duplicate it. On another site, I saw a TSB number from Ford for what sounds like a very similar problem in the 1987 models but I can't find anywhere to read what it says. The number is 881711. From what I've read in the Bronco II forums, the models tended to be very similar from year to year, so maybe the TSB for the 1987 model will help figure out what's wrong.

Because this is intermittent, I'm inclined to consider an electrical issue like corrosion interfering with proper grounding or an intermittent short in the wiring. Or maybe something intermittently interfering with the exhaust so that the O2 sensor is sending faulty info back to the ECM? Anyone have any experience with this problem or access to the TSB?

Thanks very much.
....
 
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#2
1988 into the way back machine mr Peabody - the gang here will love this classic.


Anyway 1st step with FI is always check fuel pressure, and then with KOEO observe pressure drop off. @40psi we will ck exact psi later.
You did nit say BUT the fuel filter did you change it?
Use a vacuum gauge - what is reading?
Old school vacuum tests - with eng held steady @1500 rpm the vacuum reading should remain steady a drop would indicate exhaust backpressure.
ALSO engine running spray carb cleaner at any mating surfaces, vacuum lines, anywhers you could have a vac leak - the change in eng RPM and sound would also indicate a likely vac leak...

A TSB from 1988 would likely be done OR no longer an issue as it would have shown up by now... BUT will look - that TSB # is it a NHSTA #?
 
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#3
your TSB was a good # - a ford injector* issue BUT aftermarket has answered this type issue - look at the tutorial, it will help ID fuse location, where to tap for fuel pressure reading and the cleaner process, much greater cleaning than the add to tank solutions.



*likely before the big push to so called tier3 that addressed fuel quality needed for FI engines.
 

billr

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#4
Have you checked the ECT sensor/circuit? It kind of sounds like the engine is running rich, and the ECT sensor is the heart of the "choke" system for EFI. Also check the IAT sensor, but that has far less effect on the fueling.
 
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Thank you for the fast reply!
tsb. governs. com/29l-v6177-4wd-ii-bronco-truck-ford-1987-3294.html is the website I saw it on. Look at the ones listed in August 1988. I think it must he a Ford TSB because I looked at all the federal ones I could find before asking for expert help. The filter located outside of the gas tank is what I said was emptied. I'm not completely sure if that's actually a filter or if there's maybe another one inside the gas tank. The Haynes manual is inside the vehicle at the repair shop.

I understand carburetors a lot better than EFI. I used to do some flying so I understand air density, the venturi effect, carburetor icing and why it happens but EFI is out of my league. My impression is that EFI is basically a closed system where fuel is fed to the engine based on outside air pressure (air density) that's coming in through the air box along with feedback from the O2 sensor on the exhaust. The PCV valve periodically puts some crankcase gases back into the fuel mixture to be burned. In other words, it's Voodoo!

Is your method of using carb cleaner to test for leaks safe? I don't want the mechanic to set himself on fire!
 
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#6
your TSB was a good # - a ford injector* issue BUT aftermarket has answered this type issue - look at the tutorial, it will help ID fuse location, where to tap for fuel pressure reading and the cleaner process, much greater cleaning than the add to tank solutions.



*likely before the big push to so called tier3 that addressed fuel quality needed for FI engines.
your TSB was a good # - a ford injector* issue BUT aftermarket has answered this type issue - look at the tutorial, it will help ID fuse location, where to tap for fuel pressure reading and the cleaner process, much greater cleaning than the add to tank solutions.



*likely before the big push to so called tier3 that addressed fuel quality needed for FI engines.
I like that video! It's been a while since I had the injectors tested so that might be part of the problem now. The RPM yoyos about 500 RPM at idle. Lately the base idle has decided to change itself from about 1000 up to 1500 RPM.
 

jd

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#7
Here's a long shot... An older, EFI Ford V6... Occasional loss of power at highway speed. A little black smoke from exhaust. Got worse, would load up with fuel and try to stall. Finally did stall. Running 65-mph, slowed down, lost power, quit on the side of the road in a cloud of black smoke. Towed it to mechanic who drove it a couple days and never found the problem or got it to act up. Took it home and tested sensors using a little free pamphlet from Autozone. Turned out the Air Charge Temp Sensor was intermittently open. Open told the ECM the engine was stone cold in freezing weather and richened the dickens out of the fuel mixture by opening up the injectors. Pack rat I am, there was a parts engine. Changed the ACTS and problem went away.

I had replaced the fuel filter when my daughter's first complaint was loss of power. It was severely restricted, but the new filter wasn't a fix for a bad ACTS.

Please change that fuel filter if you haven't done it recently. Vehicle may run OK with a restricted filter, but you aren't doing the fuel pump any favors asking it to push through the restriction.
 
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#8
Okay, thanks very much! That makes sense. The repair shop gave up on it after a week and a half and referred me to another shop but I've never heard of them so I stopped by a restoration/rebuilding shop today to see if they're willing to chase it down. They do great work and I've used them before. I just wasn't sure if they wanted to spend the time on it. They're interested. They can probably fabricate a new pedal assembly for it, too, to solve the problem with the clutch pedal popping off the rod to the slave cylinder.

Here's a long shot... An older, EFI Ford V6... Occasional loss of power at highway speed. A little black smoke from exhaust. Got worse, would load up with fuel and try to stall. Finally did stall. Running 65-mph, slowed down, lost power, quit on the side of the road in a cloud of black smoke. Towed it to mechanic who drove it a couple days and never found the problem or got it to act up. Took it home and tested sensors using a little free pamphlet from Autozone. Turned out the Air Charge Temp Sensor was intermittently open. Open told the ECM the engine was stone cold in freezing weather and richened the dickens out of the fuel mixture by opening up the injectors. Pack rat I am, there was a parts engine. Changed the ACTS and problem went away.

I had replaced the fuel filter when my daughter's first complaint was loss of power. It was severely restricted, but the new filter wasn't a fix for a bad ACTS.

Please change that fuel filter if you haven't done it recently. Vehicle may run OK with a restricted filter, but you aren't doing the fuel pump any favors asking it to push through the restriction.
 

billr

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#9
Did you see my reply #4? Maybe I lost you with the use of acronyms... ECT is the Engine Coolant Sensor. IAT is the Inlet Air Temperature (sensor), also called MAT (Manifold Air Temperature) and, I see above, ACT (Air Charge Temperature) by some folks.

Point is: Also have the ECT sensor checked too, it has a lot more effect on fueling than the IAT sensor. Too bad this is an old beast and live-data isn't so easy to come by, you could check those (and several more) at a glance with the right scanner.
 
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Bill, thank you for the clarification on what those initials mean. Some of them I was able to recognize and others I couldn't. That's an interesting comment about the ECT. The temp gauge is out of whack and reads high even when the temp is normal but I was thinking it has crept up some even though I have coolant in the reservoir. Checking the operating temp was on the list of things I wanted the shop to check and maybe putting in an aftermarket set of gauges that wouldn't depend on the original wiring harness. Besides, I prefer gauges instead of an idiot light that might burn out, especially for oil. I think all the suggestions given here will be a big help in figuring out what's going on. I'm very grateful to everyone who has taken the time to reply. I'm also open to the idea that correcting one problem might reveal others but if it gets this thing back to running reliably, it's cheaper than buying a new or late model 4WD. Besides, every used SUV I've seen advertised that interests me is besieged by consumer complaints so I might as well work with what's already completely paid for. I really missed my '73 Toyota Land Cruiser. Everything under the hood was so easy to get to.

Did you see my reply #4? Maybe I lost you with the use of acronyms... ECT is the Engine Coolant Sensor. IAT is the Inlet Air Temperature (sensor), also called MAT (Manifold Air Temperature) and, I see above, ACT (Air Charge Temperature) by some folks.

Point is: Also have the ECT sensor checked too, it has a lot more effect on fueling than the IAT sensor. Too bad this is an old beast and live-data isn't so easy to come by, you could check those (and several more) at a glance with the right scanner.
 

billr

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#11
I don't know if this applies to your vehicle, but a lot of GMs (and other makes?) in that era had two "ECT sensors". One was for the dash gauge, and one for the ECM input.
So, what you see may not be what the ECM is reading! The dash gauge sensor was usually 1-wire, the ECM's a 2-wire.
 

nickb2

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#12
Hi Annie.

I think your idea for a separate set of gauges is very viable and cost effective for this 1988 bronco.

We had a thread here last month or so with a 1984 LTD with same or similar issues, client was not able to ascertain proper coolant temp, oil pressure and just basically relying on "idiot lights" as you called them. Which is a very apropos way of calling them.

You will however need to keep the OEM (original equipment) wiring in place. The PCM needs that info as this is a EFI engine.

All bronco II"s as of 1988 were EFI. So the ECU (electronic control module) needs the coolant temp data to map out the adaptive memory of the EPROM to suit the driving conditions.

I highly recommend a autometer set or a equus gauge set. Those sets come with all the hardware to piggy back the necessary sensor for the ECU and if one of the OEM sensor quits, you will see it on the physical gauges instead of an idiot light flasing on and off basically telling you it's too late, engine cooked type scenario.

Annie, you stated in one of your previous posts that you feel the engine hunting for a stable idle. You wrote the idle yoyo's at 500rpm in post #6 and now idles at 1000-1500rpm. That is a substantial jump. To say the least. Being a manual, it must be close to not driveable.

Just letting go of the clutch at 1500grand will wreak havoc on the clutch and related components. Trying to move this beast (as Billr wrote) from a stand still @ 1500rpm will most certainly cause slippage and premature wear on the drivetrain. Remember, this is only a V6, not a dragster 302/5.0l. This is a daily driver and has no stall kit installed since it is a manual.

Ok, I am getting ahead of myself and as usual, probably giving more info than is needed.

You can interrogate the OBD1 system with a analog multi-meter and count the jumps of the needle to get an idea of what the ECU has to say. But that involves some skills to jumper the SPI spout terminal.

Follow this link to find out how to do that.

It is from this site, so obviously I stand by all the info here.

http://www.troublecodes.net/ford/
 

nickb2

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#13
You will most likely find a code 12. This code addresses the idle too high or too low and/or an air bypass problem.

To properly explain I will provide links. The IAC valve is a very known common issue for these engines. IAC stands for idle air control.

One of the most common symptoms commonly associated with a problematic idle air control valve is irregular idle speed. The idle air control valve is programmed to regulate and maintain the engine idle speed at a constant rate. If the valve fails or has any issues it can cause the idle speed to be thrown off. This may result in an unusually high or low idle speed, or in some cases a surging idle speed that repeatedly climbs and falls.

Another thing to check is for good vacuum. A big vacuum leak will cause a significant rise of idle. With engine at idle, listen for any hissing sound.

Read method two of the following link which pertains to your ford problem. The actual IAC is shown in the 5th diagram of method 1. It will be easy for you to spot.

http://www.wikihow.com/Check-an-Idle-Air-Control-Valve

If that checks ok, suspect carbon build-up or possible bad TPS.
 
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attached diagram show wiring to ECT and air charge sensor AKA ACT and IAT.
KOEO unplug confirm only 1 wire has voltage @5v known a VREF.... yes or no?
Plug in sensor measure voltage on the other wire - post it here and I will get the charts...
http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=20624


PS anyone interested in an OLD ford manual for this sensor has the resistance charts etc? 1.2MB PDF