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Discussion Starter #1
This might be long, but I'll try to be thorough:

I have stock gearing (I assume), and the problem has been with 31 and 33s, so I don't think it's really a tire size issue.

The bronco's never been able to make it up mild hills in OD, even when I had 31s. Even in top gear in D (4th?) it sometimes (not often) stutters a little at the end of the hill if I get on it (4000RPMs or so?).

Drives okay on flat land, can get to 70 no problem.

Under 40 I don't have problems uphill, thing runs great offroad getting to 4-5000RPM.

I do have a code 41 (lean), if it's related. I used to have an EGR code, but fixed it with a new EVR.

I also get a dull popping from the exhaust when I rev it, not while I have the throttle open, but immediately after letting off it while the motor spins down.

I'm kind of assuming my lean is related, so until someone says otherwise I'll try diagnosing them both together?

Most recently, I was on my way to offroad in Alpine. It's about 30 miles away, about 15 of that is slightly uphill. I've done this trip once before and could maintain 55ish, but that's it. No other problems.
Last time I went the truck got slower and slower over the course of five miles or so, down to the point where I only wanted to sit at 45 or so. Checked the temp gauge, and temp and oil pressure were damn near pegged, so I pulled over. Ambient temp was around 70 - normal.
Opened the hood, everything looked okay, except a wire harness fell against the exhaust manifold and started melting. (see below, the wire harness draped over the oil dipstick).



Checked the harness, and the coating on the wires hasn't melted at any point, so I'm assuming there is no damage. I can't see any, anyways. There is a diode (1N4004?) at that point that might have internal damage? Never messed with diodes, but I plan on replacing it anyways.
Didn't see coolant anywhere, didn't have a rag so I didn't open the radiator to check level.

Put it back on the freeway and stayed under 45. Managed to get to the trail, and while on the trail the engine cooled down to a little warm, but nothing serious. Truck ran absolutely perfect for the 3-4 hours we were on trail.

Back on the freeway it was fine, mostly downhill cruising at 60.

What might cause this? I'd really like to hit that same trail this Friday, but I don't want to blow the motor on the freeway!

Here's what I've done in the last year to chase down the lean issue:

New plugs, gapped .44 (pulled plugs this week, they looked brand new except the front driver side - that one looked much more tan than the others, but no wear or buildup or anything - just looked older).

Replaced exhaust from manifolds - 3" all the way, Bassani Y, new Magnaflow cat, mandrel tail.

sixlitre tune up (minus the larger gap and timing advance)

Checked timing (10 degrees on the dot)

Cleaned drop in K&N filter, oiled (old filter looked fine, just a little dirty)

Replaced PCV (checked this week, it's oil but looks operable)

Oil & filter changed (old oil looked normal)

Seafoamed through brake booster line (no smoke?! It took a while cause the engine kept wanting to stall - probably 5 minutes for half a bottle)

EGR tested - holds 15inhg vacuum steady for thirty seconds

ALMOST all vac lines replaced with rubber - there are a couple I can't get to that might be the issue. Gonna work on this tonight.

IAC cleaned - actually did this last week again and now I have a 1500RPM idle - did it die?

Checked tranny fluid - mark was right where it should be on the dipstick with engine warm and running. Fluid actually looked great - nice pink.

Replaced FPR - didn't have any fuel smell on vac side, and the fuel pressure behaved as it should have when the vac was removed, but replaced it just in case.

Replaced O2 sensor about 15 months ago.

Last year I did a simple compression test - all plugs removed, engine warm, battery charged. All were something like 115?? I do remember that they were all within 5-10% of each other.

Checked TPS - voltage scaled smooth from 5.0v open to 1.03v closed. Nonadjustable type.

New fuel filters. I actually found out yesterday that the 86 has TWO filters, and changed the second one. The old one looked pretty bad, so I wonder if this might be the cause? I'll try it on the freeway tomorrow.

Kind of wondered if the MSD coil was shitting, so I swapped in my old motorcraft one, put a spark plug on the end of the dizzy cable, laid it on the exhaust manifold, and cranked (with WOT) - spark was blue with a possibly very slight orange - I think it's fine? Swapping didn't make a difference in ride.

Checked rad for coolant level - it was a little low, but seemed good enough. Topped off just in case.

The truck seems to heat up faster now (from cold), but I haven't noticed it overheat. Maybe shows a little warmer than usual? The oil pressure is pretty much always 'high' now, but I've read that the gauge is actually BS and if it reads high then it's going bad. Thoughts?

I've checked fuel pressure KOEO and MAYBE KOER and I remember it being to spec, but I don't remember if it kept pressure for more than 5 minutes.
I haven't tried it while driving uphill on the freeway - I wonder if doing that will show me a drop? Gonna grab a gauge again today and try it out. I'm suspecting one/both of the fuel pumps? I've run out of gas a few times. Not sure how to diagnose fuel volume?

Any help on the overheat and/or lean issue is appreciated!!:beer

I'll paypal $50 to anyone who suggests the correct answer for the code 41.
 

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i'd lean towards the fuel pressure regulator while under heavy load is failing
 

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Discussion Starter #3
i'd lean towards the fuel pressure regulator while under heavy load is failing
Oh yeah, forgot I did that too...
Replaced FPR - didn't have any fuel smell on vac side, and the fuel pressure behaved as it should have when the vac was removed, but replaced it just in case.
 

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oh... nvm then


do you have the equipment to do a leakdown test?
 

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Discussion Starter #5
No, although I've read that it's a more reliable or sensitive version of a compression test?
I heard HF has testers for it, but don't know if they're reliable enough to use.
 

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My stock 86 302 EFI tends to lose a bit of power going up steep hills with power to weight ratio but my AOD will kick in and it downshifts nicely into 3rd no problem....my 302 long block was new in 2008 and the AOD was rebuilt in 2004...sooooo

Any chance showing fault code: 44 .....thermactor air injection system fault, is a vaccum leak in the emissions system which affects performance dramatically with loss of power up/down hill, ignition detonation, bucking until the rpms smooth out in stop & go traffic, it's ususally the "check valve" on top of the exhaust air injection cross over tube bolted to the back of the cylinder heads that burns thru over time from extreme heat /moisture causing a vaccum leak sucking in and changing the EGR airstream DOWN and out the CAT starving the system of oxygen rather then an UP air stream etc.

Maybe a stretch for this but check anyway......

Good Luck ~ :thumbup
 

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Discussion Starter #8
Check your Air Filter, PCV and MAP. See this link:

MAP or BAP? Which Sensor is it?
Air filter's perfect, PCV looks good (rattles loosely, it's about 15 months old), I was thinking perhaps MAP. Other than verifying that the vacuum lines driving it are good, what else can I check? I've read that the MAP signal can't be read by a DVOM unless it read freq, which I don't have.
 

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No, although I've read that it's a more reliable or sensitive version of a compression test?
I heard HF has testers for it, but don't know if they're reliable enough to use.
yeah testers like 20 bucks, but you need an air compressor too

I'd recommend doing it, if you hear air coming out your intake (i recommend removing the intake tubes going to the filter so you can have your ear next to the throttle body and hear any air escaping better) then you know your intake valve for whatever cylinder your doing the test on is bad, same with exhaust, and remove your dipstick as well and if you hear air coming out the dipstick tube then you have rings that arent sealing good

but i'd also thoroughly read the link about MAP or BAP that was posted
 

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Seattle FSB: I read your link great info thanks!

I replaced all my sensors including the MAP not too long ago I just think Broncos are under powered at power to weight, 185 HP with 139 HP at 3500 rpms which I'll never see (Haynes Manual) ...lol lol...but mine runs really good now....:chili:

Good Luck ~ :thumbup
 

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My stock 86 302 EFI tends to lose a bit of power going up steep hills with power to weight ratio but my AOD will kick in and it downshifts nicely into 3rd no problem....my 302 long block was new in 2008 and the AOD was rebuilt in 2004...sooooo

Any chance showing fault code: 44 .....thermactor air injection system fault, is a vaccum leak in the emissions system which affects performance dramatically with loss of power up/down hill, ignition detonation, bucking until the rpms smooth out in stop & go traffic, it's ususally the "check valve" on top of the exhaust air injection cross over tube bolted to the back of the cylinder heads that burns thru over time from extreme heat /moisture causing a vaccum leak sucking in and changing the EGR airstream DOWN and out the CAT starving the system of oxygen rather then an UP air stream etc.

Maybe a stretch for this but check anyway......

Good Luck ~ :thumbup
I didn't think any of the check valves/tubes would throw any kind of codes? From what I know, the closest your computer sees is at the solenoids which control vacuum to the valve, but there is no way of the computer knowing whether the valves are bad when the solenoids apply vacuum to the valves.
 

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Discussion Starter #13
Read my link. It explains how the MAP/BAP works and how to test it.


For those that do not care to read, I suspect that you may have high vacuum, which represents low load resulting in a lean fuel condition. Symptoms can be surging, bucking, rough idle, detonation and a lean fuel condition.
There isn't anything about the 86 on there - do you know if it's MAP or BAP, and whether it's voltage ref or frequency ref?

If the BAP is atmospheric pressure, then I assume it wouldn't be connected to the manifold for vacuum. If that's the case then I suppose I have a MAP.
Using a DVOM, how can I tell if it's voltage or frequency reference?

Thanks for the help so far.
 

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Discussion Starter #14
My stock 86 302 EFI tends to lose a bit of power going up steep hills with power to weight ratio but my AOD will kick in and it downshifts nicely into 3rd no problem....my 302 long block was new in 2008 and the AOD was rebuilt in 2004...sooooo

Any chance showing fault code: 44 .....thermactor air injection system fault, is a vaccum leak in the emissions system which affects performance dramatically with loss of power up/down hill, ignition detonation, bucking until the rpms smooth out in stop & go traffic, it's ususally the "check valve" on top of the exhaust air injection cross over tube bolted to the back of the cylinder heads that burns thru over time from extreme heat /moisture causing a vaccum leak sucking in and changing the EGR airstream DOWN and out the CAT starving the system of oxygen rather then an UP air stream etc.

Maybe a stretch for this but check anyway......

Good Luck ~ :thumbup
Thanks for the info... I haven't dug into it yet, but the "diverter valve" in the below pic (click for bigger) doesn't hold vacuum at all when I apply vac to the line on top of it... Not sure if it's supposed to, any idea?


Oh, and no, as of last time I ran codes in the spring I only had 41.
I'll run codes again this weekend since I started overheating on the freeway.
 

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There isn't anything about the 86 on there - do you know if it's MAP or BAP, and whether it's voltage ref or frequency ref?

If the BAP is atmospheric pressure, then I assume it wouldn't be connected to the manifold for vacuum. If that's the case then I suppose I have a MAP.
Using a DVOM, how can I tell if it's voltage or frequency reference?

Thanks for the help so far.
You have MAP. I believe that most Fords use a variable frequency signal MAP.
 

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maybe a cat is starting to collapse... had somewhat same problem in a ranger... long shot though
 

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Discussion Starter #18
You have MAP. I believe that most Fords use a variable frequency signal MAP.
Forgot to mention, I connected a vac gauge up to the manifold tree and got an absolutely steady 20 in. hg. all the way up to 5000RPMs when parked. That should mean that vacuum going to the MAP wouldn't be too high, correct?

I suppose it really needs to be watched while I'm going uphill on the freeway. I'll try that in particular this weekend when there's some light out.

Without a tachometer or a DVOM that handles freq, I don't see anything else I can do to test the MAP, other than swap in a new one.
 

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This has happened since I got the truck, cat was the first thing replaced.
when you lose power, does your rpm stay at , or does it raise? many people i know have the rpm raise which leades to torque converters or trans, usually not fords though.
 

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Discussion Starter #20
Troubleshooting list:

-Pull codes again

-Check out the thermactor air injection system, in particular the diverter valve may need replacement

-Run new vac line to MAP

-Connect vac gauge to tree, run up the highway hills, note readings

-Replace MAP?
 
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