Questions regarding how the EEC works seem tocome up fairly regularly and the answers are often varied. I have put together information gathered over the last few years into an article on how the EEC works. Read and let me know how you like it. CONSTRUCTIVE criticism or additional info is always welcome.
Tom Moss
88 GT 5spd Vert 3:73s, Flowmaster catbacks, stock cam +4°, GT40P heads & 1.7 rockers, Jet-Hot coated MAC P headers, 97 Explorer intake, 65mm TB and 19# Explorer injectors. 277RWHP/330RWTQ
I noticed you mentioned that the O2 sensors have to be a certain distance from the ports of the heads. How far away can they be? I have long tube headers, and they're just a few inches away from the collectors. Is that too far? Another thing, I thought our O2 sensors have a built in heater in them? Is this not adequate?
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89 GT Convertible 306, Port Polished GT40 Aluminum Heads,Self polished GT40 Upper and lower Intake, 30 lbs injectors, carter intank fuel pump, bosch piggyback inline fuel pump, Intercooled Procharger, Southside lower rear control arms, suspension technik lowering springs, tokico rear shocks, 4:11 gears, aluminum driveshaft, weld in subframe connectors
There is no exact distance, it just has to be close enough to allow the sensors to stay hot enough to work correctly. If your not having any running rich problems, you're probably OK. Yes, the O2 sensors do have a heater but that won't carry them alone.
I don't think HEGO's will cool, because they are heated. The main reason is that the HEGO's are not taking O2 readings continuously. The ECU reads them in intervals that is in correspondence with crankshaft rotation. So it is a timed event. The ECU can be reprogrammed to account for a greater time difference in O2 readings. I think the factory is like 14-15 inches.
Just another tip, usually a value less than one will result in enrichment.
Murdock
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Originally posted by Murdock I don't think HEGO's will cool, because they are heated. The main reason is that the HEGO's are not taking O2 readings continuously. The ECU reads them in intervals that is in correspondence with crankshaft rotation. So it is a timed event. The ECU can be reprogrammed to account for a greater time difference in O2 readings. I think the factory is like 14-15 inches.
Just another tip, usually a value less than one will result in enrichment.
Murdock
Let's take this a little farther. Murdock is saying that the EEC times it's sample of the O2 sensors to coordinate with the exhaust pulse reaching the O2 sensors in the H-pipe. I thought the sensors also needed hot exhaust gas to reach full operating temp. Is that not the case? Will the heater carry the O2 without exhaust gas heat? 14-15 inches from what point of reference - Collector tube? The stock primary tubes are different lengths, so their not a reference point right? Do you reprogram the time interval for the sample with a Tweecer or similar tool when installing long tubes? Or are they close enough to the same length from the engine to the sensor to use the stock sample timing? I know you mentioned cautioning long tube users about proper O2 sensor function so we would like to pick your brain a little more.
Well I noticed when I drive around, during open loop...my car is so much quicker. As it heats up, I find that it gets a little slower. Mind you, right now I have the pressure right down...and my supercharger isn't hooked up. The intake is still on the supercharger...so it's pulling through the impeller and the intercooler. But it's still fast when the blower belt is disconnected.
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89 GT Convertible 306, Port Polished GT40 Aluminum Heads,Self polished GT40 Upper and lower Intake, 30 lbs injectors, carter intank fuel pump, bosch piggyback inline fuel pump, Intercooled Procharger, Southside lower rear control arms, suspension technik lowering springs, tokico rear shocks, 4:11 gears, aluminum driveshaft, weld in subframe connectors
The reading of the O2s by the EEC is a timed event. A Tweecer, EEC Tuner, etc will allow you to change the exhaust pulse delay to compensate for long tube headers. My Hookers put the O2s WAY back, maybe 10 inches in front of the tranny crossmember. It hasn't caused any rich problems but I'm still trying to tweek for the best exhaust pulse delay values.
The actual values in the EXHAUST_PULSE_DELAY table (load vs rpm) are based on the time the injector fires until the O2 sensor sees that pulse.
Thanks 86Cobra that helps, but that doesn't answer my question about whether exhaust temps are needed for proper operation of the sensors. It does give me a clue though since your bungs have moved so far back. I have read before from some very reliable sources - namely Brian at HTM that the heat is needed also. Maybe not.
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Tom Moss
88 GT 5spd Vert 3:73s, Flowmaster catbacks, stock cam +4°, GT40P heads & 1.7 rockers, Jet-Hot coated MAC P headers, 97 Explorer intake, 65mm TB and 19# Explorer injectors. 277RWHP/330RWTQ
Yeah, I had always heard that heat would be a problem. So far it hasn't been an issue for me though. Then again, I adjust my a/f ratio with the Tweecer so I may not notice a slight enrichment caused by lack of O2 heat.
Yes.. the O2 sensors need the hot exhaust gasses to "stay" at its operating temperature. The O2's need to have the built it heater for start-up. It would be like pre-heating the oven, or eliminating the sudden rise in temperature that might fracture the sensor. 15 inches would be from the exhaust valve. If the HEGO does not stay at operating temperature it will cause a lean condition. The problem we had with a friends car was the long tubes moved the sensor so the ECU was pulsing at a point were it would read a large oxygen content and started adding fuel. When looking to purchase long tubes on a EFI car it is beneficial to get some sort of coating. We did a pro street Mustang for a customer that had his headers Jet-Hoted. It made a huge difference. The exhaust did not cool as fast.
86Cobra, what values have you tried in the table. 16-18 through-out the table should be close. I have played with this a bit on the dyno.
Murdock
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Originally posted by Murdock 86Cobra, what values have you tried in the table. 16-18 through-out the table should be close. I have played with this a bit on the dyno.
Thanks for the input. I had it at 20. Unfortunately I don't keep my car in running condition long enough to really experiment!
I would just like to say thank you all for this information which I have learned. I'm the kind of person who likes to know everything about everything, and this thread has helped me alot to further understand the way in which the proccesor controls various functions.
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97 Cobra #777 Blk/Blk
ProCharger P600B 7psi w/3 core intercooler, off road x-pipe, flows, pro kit, oil separator mod.
Your over in Springfield? Are you coming up to Columbus for the swap meet? It would be cool to meet someone off the board. There is actually a Mustang club in Springfield called MidOhioStreetStang's.
Murdock
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~Chip Wizard Performance~
EEC-IV & EEC-V Custom Performance Chips
-4 Custom Programs / $250
-30 day free reburns
-Reburns after 30 days / $40
ive yet to get in there an swap over to Mas ive got everything but the CAI to get it all hooked up. at the moment with the SD and long tubes it runs a tad rich actaully pretty rich hopefully i get all together this weekend and that will smooth it out a bit more.
j
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2004 mustang gt
Update: JLT CAI, SLP LM2 catback,
Parts in the basement : To much to list. heres a hint..it involves a watts link and turbos.
How EEC Works 
I'll try 16-18.
