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Old 03-21-2016, 02:56 PM   #1
ArchEnemy
 
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Idle/ECU/Sensor issues

Okay so about 3 months ago I started having issues with extremely rough cold starts, no warm up cycle, and after achieving normal operating temperature the car would stall sporadically after letting off throttle to coast to a stop or park or whatever. After stalling it would take a few seconds of cranking and WOT to get it started again and no CEL. It was not a sudden onset thing, it gradually got worse, and now when the vehicle is hot it almost always stalls after letting off the throttle. So what I am working with: EJ1, B20/b18c1 head, p28 ecu with crome tune. What I have done so far: Cleaned and tested original IACV, after no improvement, replaced IACV with functional used one, still no improvement. After replacing the IACV I attempted to set reset the idle, and the car will not idle with IACV unplugged for me to set the idle, even with the idle screw completely removed. They only success I have had is removing the vacuum line to the IM, and I tried setting the idle that way and it did not work. For giggles I replaced, plugs, wires, cap, rotor, coil, and ignitor (control module), timing at warm up and cooling fan temperature is spot on. Replaced, Coolant temp sensor, map sensor, o2 sensor was replaced about a year ago so I have not touched that yet. Also had a valve adjustment and compression test done about a month ago and #1 showed 120psi and 2-4 tested at ~128, no leakage. Tested fuel pressure, 42 at idle with vacuum line in place, and 50psi unplugged. Pinched return line and pressure rested at 72psi, after key off, fuel pressure held at 42, so I think thats all good.

I tested the intake air temp sensor (air charge) and the input (reference) voltage is only reading 3.4v which I thought was supposed to be right around 5v. One of the videos I found on youtube said the ECU could be at fault for improper reference voltage so I reset the ECU to be sure and it still only read 3.4v. The IAT resistance was ~1970 ohms, and have not been able to find what a factory resistance for the IAT is. Also tested the TPS and at closed throttle it read .47v and WOT read 3.6v which I thought was also supposed to read ~5v, and no sporadic jumping between closed throttle and WOT.

In my experience, I have never seen an bad o2 sensor have a major affect like idling and stalling and cold start. But I will test the resistance on that turd as soon as I can track down the acceptable ranges.

So my questions are, first and foremost, WTF? Secondly does (or could) the TPS voltage reading affect the IAT reference voltage? I do not think that it would, but I have to ask to be sure because I am running out of ideas. Since this is an issue that gradually got worse to the point where it is at now, could it really be the ECU? Should I plan on replacing the TPS and even if so, the reference voltage for the IAT not being ~5v is concerning.

Update***

Picked up a TPS, and now I can not get the new one or old one to read over 2v now, not to mention I cant even set the closed throttle at .5v because I have to twist the TPS past the bolt holes in order to get there....

Thanks in advance!

Last edited by ArchEnemy; 03-21-2016 at 06:31 PM.. Reason: Update
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Old 03-22-2016, 02:56 PM   #2
cbaracing
 
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what does it do with a stock ecu?
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Old 03-22-2016, 04:07 PM   #3
ArchEnemy
 
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Quote:
Originally Posted by cbaracing View Post
what does it do with a stock ecu?
Have not tried one, nor do I have one, nor do I know anyone nearby that has one unfortunately. I spent all morning checking the harness and could not find anything suspicous, checked voltage wires coming from the ECU with Key on engine off and everything that was supposed to read 5v was at 5v, and the same goes for engine running. the only thing I noticed as I made another attempt to set idle, was that when i turned the blower on high and the rear defroster, the idle dropped SUPER low, ~150 RPM. I read recently that the Canadian (which mine is) model Civics do not have ELD, so could it be the alternator? It keeps the battery charged, just seems like it can not handle loads. When I was checking the engine harness I pulled the connector for the alternator and it seemed fine, but I cleaned it up with electric parts cleaner and still no dice.
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Old 03-23-2016, 10:52 PM   #4
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Some tool on HT locked my thread because I questioned whether a faulty injector could cause 70psi compression loss, anyone know anything about this? I did not doubt it, I just don't know.
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