A Super-Ultimate 3FE Diagnostics Thread - Let the Battle of Wits Begin (1 Viewer)

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down in a hole.
Put em one in front of the other just downstream of the y? You kinda loose the distinction for the ecu to recognize if one bank has gone off the other, but if your injectors are good and the harness is good, you likely don’t have much variance between banks...I have to think that being so close to the dump is giving a false rich return... theoretically, you could put one sensor in and pair the output wires to go back to the ecu and trick it into thinking there are 2 sensors. It won’t care if both sensors return the same values, and as long at the mechanical and electrical end of the injection is good, it won’t either...
 

Kleatus

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Can you extend each collector pipe and move the Y backwards? Mine is very similar but my collector pipes are longer (pictured earlier in thread). If it’s already off that’s not too much hassle. You’ve come this far - might as well try to get it as close to “right” as possible! I’m sure someone can chime in as to OEM distance down the pipe from the manifold.
 

lelandEOD

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Can you extend each collector pipe and move the Y backwards? Mine is very similar but my collector pipes are longer (pictured earlier in thread). If it’s already off that’s not too much hassle. You’ve come this far - might as well try to get it as close to “right” as possible! I’m sure someone can chime in as to OEM distance down the pipe from the manifold.

Yeah, I have a buddy with an exhaust bending machine so I'm going to scab something together temporarily to test the concept. If it makes a difference in my air/fuel ratios, I'll just take the truck to a shop and have them make a new exhaust system.
 
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Sort of....
The base timing can be adjusted just as many older engines - loosening the distributor hold down bolt and turning the distributor. The ECU simply starts with the base curve and has a pre-defined amount of deviation it can induce via the preprogrammed timing maps, which are selected based on things such as engine temperature, throttle position, load, rpm, etc. On an older engine you can tune the mechanical or vacuum advance curve (changing springs, weights, etc) to mitigate such changes as EGR removal. With the 3FE you can set the base timing only, and the timing curve off of base timing is determined by the ECU.

The ECU is programmed to adjust the timing with the EGR functional - which when present and functional lowers combustion temperature, allowing more timing advance. When the EGR is removed the amount of advance the ECU is commanding can be inappropriate unless the base timing is dialed back. So for me I have my timing set so that I get no pinging at cruise load/rpm, even if it means giving up a degree or two at WOT, which I hardly use anyway.



My truck is de-smogged (no air pump or EGR), head shaved, base timing advanced (10 I think), below shows my O2 sensor placement. No trouble with lean idle that I can tell. It doesn't stumble or smell like a lean mix but I may just be missing it. In idle after warm up, it should be in closed loop so the feedback from the O2 sensors would adjust injector time to get the correct A/F ratio. I am curious what results you get relocating the o2 sensors. The only issue I have read is the non heated ones being too far down the pipe and not heating up correctly.




upload_2018-3-3_10-33-49.png


Thanks for the info on the TPS. I knew they were different PN but not why.
 
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Something else I thought of, the 3fe uses timing to adjust idle along with the ISCV. If you have AC, is your AC signal to the ECU turned off (not sure if this matters in test mode)? When you jumper the test connector that should put you on base timing and at the correct RPM. If RPM is low, the timing may not be correct, I'm pretty sure it will sit at 650 with 7 deg of base timing. If I recall it is tricky getting the distributor set down correctly. The throttle bypass screw on the throttle body should be fully closed. The only other issue with lean mix is a vacuum leak someplace down stream of the AFM.
 
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The fact your rpm drops when you insert the test connector has me bugged. The ISCV should be able to compensate to keep idle at target as long as the IDL contact in the TPS is closed. I have found that the ECU/ISCV can get confused in some cases and not operate as expected, it happened to me when I had a high idle due to the throttle plate not closing enough. IDL contact was closed yet it would not go into closed loop idle control. I could open the bypass screw on the throttle body and then close it, idle would come in at 650. This had me really stumped for a while. I also wonder if the timing advance is not compensating for a malfunctioning ISCV, since it is dropping RPM when the test connector is installed and the ECU falls to the base timing. The book states timing can advance as much as 5 deg to stabilize idle. A malfunctioning ISCV (or blocked air passage) masked by timing advance could maybe account for a lean idle. Does your lean condition go away at off idle/part throttle stable operation?
 

lelandEOD

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The fact your rpm drops when you insert the test connector has me bugged. The ISCV should be able to compensate to keep idle at target as long as the IDL contact in the TPS is closed. I have found that the ECU/ISCV can get confused in some cases and not operate as expected, it happened to me when I had a high idle due to the throttle plate not closing enough. IDL contact was closed yet it would not go into closed loop idle control. I could open the bypass screw on the throttle body and then close it, idle would come in at 650. This had me really stumped for a while. I also wonder if the timing advance is not compensating for a malfunctioning ISCV, since it is dropping RPM when the test connector is installed and the ECU falls to the base timing. The book states timing can advance as much as 5 deg to stabilize idle. A malfunctioning ISCV (or blocked air passage) masked by timing advance could maybe account for a lean idle. Does your lean condition go away at off idle/part throttle stable operation?

Brother,
Your responses are really making me think relocating the O2s won't change my problem. I'll need to reassemble the exhaust before I can fire it up again. I will likely make a video that shows what the engine in doing when I short the test connector. Perhaps someone can elaborate. I thought the drop in idle was due to the ECU's altitude compensation being overridden. I am at 4500 ft so I don't know if that explains it or not.
 
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The ISCV should still be able to compensate if that is the case. The 3FE ECU does contain the D IS121 HAC sensor.
 

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also verify your engine ground is solid. And the harness ground to the engine for the injectors must be good. I checked my Te1 to E1 reaction to idle tonight when I got home from work, I didn't have a tach on it but the idle did change a bit, a little rougher and maybe slightly lower but it is hard to tell for sure without a tach. A definite change in idle stability though.
 
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lelandEOD

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It oughta idle down as the idle timing goes from the dynamic 12*Btdc target down to the test setting of 7*BTDC.

Ok, but should it idle down below 650 when you set the timing? I can't believe I'm still confused on this issue.

Btw,
I'm recovering from a triple-whammy of kindergarten-induced cold, conjunctivitis, and strep. I hope to get back to the truck in a day or two.
 

lelandEOD

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I was able to move the O2s approximately 22" farther downstream and I made sure they were both equal distance from the manifold before welding the bungs. The new O-ring came in the mail as well so I replaced the old one between the ISC valve motor and housing and re-smoke-checked the engine.


No change in the AFR :notworthy:.
 
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lelandEOD

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However,
I think I've been screwing up the ignition timing procedure.

I was setting the base timing to 7° BTDC (engine at 650rpm and check connector jumped) correctly *at least I think so*. But I was screwing up on step #4 - rechecking the timing with the jumper wire disconnected. I added 12° of advance into my digital timing light and thought it was pretty close to lining up with the mark in the window (10° was more precise) But I just realized today that I am seeing the 7° BTDC BB rather than the TDC mark. DO'H!

In order to get the TDC mark aligned in the window (not the 7° BTDC BB), I have to add 18° of advance into the timing light. This seems wrong... I need a coffee.
 
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Set the timing with te to e1 jumped to 7 degrees which is the bb. Keep your timing light setting set at 0 when you do this. You need a digital waveform of the o2 sensor voltage to see what it is reading. How old are your o2 sensors and what brand are they?
 

lelandEOD

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I did set the timing to 7° BTDC (BB) with the check connector jumped but when I re-check it after removing the jumper, I'm not getting the degree of advance specified in the manual. Check out this video:



The O2s are Denso and were bought new for the rebuild.
 

Kleatus

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Do you still have janky voltages for temp sensor as described earlier on...? I think you need to get to the bottom of that.

Can you test/verify that your wideband is indeed giving you correct values?
 

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