This is actually a continuation of the thermactor thread a couple of days ago, since I have some similar problems.

1986 Ford Bronco 5.0 EFI

Symptoms:
Runs rough, backfires, poor power under load
Right exhaust manifold gets red hot under load
Cracked right manifold is chirpping

Codes:
(25) knock not sensed during dynamic response test
(44) thermactor air system or secondary IAS inoprative
(77) operator error during cylinder balance test

Replaced, tested & Bypassed components:
Fuel & air filters replaced
New distributor, ignition module, plugs, wires and coil
Rebuilt engine, water pump and all components cleaned
New knock sensor, temp sensor & thermastat
Fuel pressure, volume & injectors tested
Thermactor air pump belt removed, vac line plugged
EGR vac line plugged, catalytic convertor hollowed out

Progress made:
Faulty base timing discovered by auto mechanic, Harmonic balancer had slipped on its internal rubber causing the timing mark to be 10 degrees retarded, This caused lean surge symptoms and exhaust overheating. With this corrected the engine ran wayyyyy better and the exhaust only glowed faintly after going up some serious hills at full throttle.

Unfortunately the timing light showed that the EFI system was still retarding the base timing at idle, at full throttle the timing advance was only 10 base time + 10 advance = 20 BTDC total (it should be 30 to 50 BTDC total advance)
The engine was also running on the hot side, close to red

So what is retarding my timing advance? The mechanic wasnt sure but said my O2 sensor was probablly fried and that the O2 sensor reading is needed for the EFI system to go into closed loop? I was under the impression that the coolant sensor controlled open closed loop and the O2 sensor only controlled fuel injection duration? Is something triggering my knock sensor to retard timing? if my knock sensor has a problem does the computer automatically retard timing?

Well at least now I know the cause, if anyone out there knows what needs fixing I would be very thankful. Thanks.

 

If I hear anything about glowing exhaust, I immediately think of a plugged catalytic converter.

 

JBronco,

I would normally agree with you but it says they have been hollowed out. Still, it doesn't mean there isn't some other part of the system clogged.

Not certain whether the retard is automatic with a failed knock sensor but it certainly won't compensate if there IS knock or ping present.

Does the right hand manifold still have a heat riser valve in it? Or is it an actual EFI manifold? I only ask because it really sounds like some sort of blockage on that side. And its probably chirping because of the crack.

You are running an EFI engine that relys on a lot of input from sensors that are not doing anything with all the emissions stuff disconnected or inoperative. The ECM assumes a certain amount of exhaust gas recovery and uses the EGR positioning sensor to determine how much. Without that signal it will pick some default value or trigger a code and not do anything to compensate for it. The exhaust gases must be handled this way because they change the amount of intake air present and therefore the fuel-air ratio. The computer can only compensate within the physical constraints of the components it has to work with. The IAC can only let so much air into the system. Without the air injection to the heads from the smog pump, the O2 sensor is getting "rich" readings from the exhaust gases because there is no fresh air added to the mix to dilute it.

 

I have the 5.8 351w. The exhaust pipe was getting red hot just before the muffler. Just by chance found my spark wires on wrong when replacing cap. What kind of motor do you have 302 or 302 HO?

 

regular 302 for an 86, seventh digit in serial # is "N".
I did not hollow out or remove any emmission devices until I started to have serious drivability problems, I will reconnect them as they dont seem to be the root problem.
The muffler is also new because it actually blew off when my problems started.

If I am getting high temp on my dash gauge does that mean I am in closed loop?

 

is it possible that they sent me an engine with a different spark plug sequence "83 Black & Chrome"? My original was counterclockwise 1,5,4,2,6,3,7,8 and my engine was right side from front 1,2,3,4 left side 5,6,7,8

all of this still doesnt explain why my ignition timing wont advance properly

 

Im not sure what a heat riser is Greystreak92, but the thermactor system seems to have plumbing into the upstream and downstream of the exhaust manifold. I read somwere that the air pump is only ever active during cold open loop though

 

If thats what you have, then there is no heat riser valve in the manifold. It was just a thought. 83 Black & Chrome went for the only other thing I could think of...reversed firing order somewhere. Getting an incorrect engine would require getting a 1995 or later 302.

The smog pump is always running. Its the EGR that only opens at certain times.

 

when i put my long block in I noticed it was the same flat rocker as my original engine and not the improved roller rockers of newer engines, so I assume this proves I have the correct engine.
besides that the problem has chased this engine from my original engine, somthing in the engine managment system is foobared, but what?

 

Oh I didn't notice the part about the hollowed out cat. I don't know then.

 

If I had to take a guess from what's already been stated... I'd say that it's either a bad O2, or the ECU. Had a friend with a chevy a few years ago. Same type of problem, and it ended up being a windshield leak onto the computer, caused a short, and glowing exhaust manifolds, melted cat, and also blew the muff off. You may concider having the computer checked, or get one from the local yard. Good luck.

 

I agree with resto on getting the computer checked.I would especially get the O2 sensor checked.If the manifold is cracked it could very well be drawing in outside air causing a lean condition on the right side.The computer would compensate for the lean mixture by changing the injector dwell time until it reached its max.Once the max dwell is reached it would begin to retard timing to try to correct the lean mixture.Good luck.

 

I didnt even think about an air/fuel ratio imbalance causing the computer to change timing, thanks.
replaced my exhaust with a good one from the scrap yard, and fixed two vacumm leaks at EGR solenoid and thermactor valve.
I was thinking vacumm leaks didnt matter when I was at "Wide Open Throttle" I just figured out that these run off of accumulator vacumm, not manifold vacumm. Somthin new to learn every day!
Engine is running quieter, cooler and better than ever before.
I will check timing and clear and check codes tommorow, keeping my fingers crossed, I really dont want to have to replace the main computer

 

code 44 is gone
new code 41 "lean O2 sensor reading"
code 25 still there "knock sensor not detected during test"
timing light still shows my system is going retarded

I will thoroughly check this knock sensor and wiring
I will double check fuel rail pressure at various RPM's

I have a question, if a wire in the injector harness goes bad, could that cause the whole system to go retarded or read lean

 

These engines act weird with a timing ling when reving them up. It will go all over the place. It's hard to check the advance unless you have a good scan tool ( about $3000 from Snap-On). My 5.0 88 Mustang has always done this.
It sounds to me like you have a bad ECM. My mom's Olds did that. It would retard the timing because it said that it was receiving a signal from the knock sensor (even when it was unplugged).
I replaced the ECM and it runs like a new one.
It sounds like that portion of the ECM may be faulty. You can get one from a junk yard, but take your old one to match up the numbers. There are different ones for different trannies and calibrations.
Jimmy