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89 crx
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Discussion Starter #1
p28 tuned in crome, check engine light comes on but cant pull the code. motor idle surges like the IACV isnt working. 1-1.5k rpms. new IACV, new wires and pins from ECU to IACV. back probed at IACV 4.9v with check engine light on. one time i got the bright idea to pull the hell over and pop the ecu off the studs and set it on the carpet. check engine light turns off and car runs fine for a few days. next time it happened i pulled over and tryed messing with the harness and plugs, this didnt fix anything so i slapped the top of the ecu and everything turned back normal. im not joking, im not trying to mess with anyone the obvious thing is that it have a short or loose connection in the ECU. just what can i do to find and fix this problem. visual on circuits is good everything looks like its soldered perfectly. idk what too do other than get a new ecu... any ideas?
 

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if slapping, shaking or moving the ECU around is working, then you most probably have a loose contact at the ECU plug and not the ECU itself. just to be sure, take the cover off the ECU and see if any of the pins going from the plug receptacle to the board is broken / damaged. if not, you will need to carefully check every pun in the wiring harness plugs. that can be a major pain in the ass but you will need to face it.
 

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if slapping, shaking or moving the ECU around is working, then you most probably have a loose contact at the ECU plug and not the ECU itself. just to be sure, take the cover off the ECU and see if any of the pins going from the plug receptacle to the board is broken / damaged. if not, you will need to carefully check every pun in the wiring harness plugs. that can be a major pain in the ass but you will need to face it.
^^^trust what he says, everything i've read that he says about ECU's is legit. he knows his stuff.
 

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89 crx
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Discussion Starter #9
if slapping, shaking or moving the ECU around is working, then you most probably have a loose contact at the ECU plug and not the ECU itself. just to be sure, take the cover off the ECU and see if any of the pins going from the plug receptacle to the board is broken / damaged. if not, you will need to carefully check every pun in the wiring harness plugs. that can be a major pain in the ass but you will need to face it.
i have looked at every thing on the board its on there good nothing looks blown, popped or leaking plug pins are contacting the ecu pins. (and continuity checks out) the IACV asks like its totally taking a huge crap but i cant pull the ecu code. so this makes me think its the ecu. (tin whiskers) im using a chipped p28, the soldering for the ZIF and other shit isnt done in a clean room adding tons of impurity and tin to the mix makes an awesome tin whisker growing environment, slapping the ecu fixes it every time. thinking about duct taping it to an ultra sonic cleaner for an hour. what are your thoughts
 

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tin whiskers could be a possibility. cleaning never hurts. however, it sounds like a loose contact problem to me.

you may want to get the cleaning done first. then, pull a couple of test wires from near the IACV coupler on the engine bay side and corresponding pins on the ECU side [I used two very small alligator clips to attach to the L shaped pins that meet the board. one clip to the IACV pin and the other to the 12V pin].

when the ECU pops a code, use a multimeter to check resistance on the ECU side and pulse frequency on the IACV side. if there is a continuity problem, you will see wrong resistance values on the ECU side and / or wrong frequency values on the IACV side. if I remember correctly, the resistance should be around 14 ohm [you can test that by measuring the IACV pins directly] and the frequency somewhere between 400 to 500 Hz.
 

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The Wife and the Car
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If this happened to me.
1. Identify if its an ECU problem or a wiring / IAC issue. I would do this by swaping the ECU to another Car. If I didnt have a spare car I would send it to a mate who has the same car. i.e. Cynide. And see if he has the same issue.

2. If its proved the ECU is fine then its simple fix replace the IAC and run fresh wire to the ECU.

3. If it was the ECU. Confirmed.
I would use a de-soldering wick. Or Pump. Suck out all the solder points that where touched by the guy who chiped the ECU. And then re-solder each point with good flux and solder. I would also trace the signal back from IAC pin to the Processor. Touching up all the points along the way.

Dont know about whiskers. But have had similar issues with dead solder. Once spent 3 days with a board. Finally cracked it when I found putting pressure of the scope probe to the pin caused it to fire up. (I have a test gig so I can test on the bench).

Lastly if going over the solder points fresh dont solve it. I would replace the Transistor which controls the IAC valve. Im sorry I dont have time to dig it up. But Im pretty sure one Transistor handles the IAC valve. Its a pretty common and easy to get one. If I get some time will trace the line and get back to you.

Like 007 says. Hook up a scope or MM to the IAC out and see what kind of signal you get.
 

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Discussion Starter #12
ecu will throw other codes if i unplug stuff from the engine, including the IACV. but when it gets that "wild hair" the cell light stays solid when i jump the connector.

is there some sorta spray on coating i can use after a good cleaning?
 

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a CEL 0. could it be that because of said "wild hair" or some other reason the chip / emulator is not visible to the MCU anymore and it goes into limp mode?

idling at 1500 RPM is typically an indicator of that and it happened to me less than a week ago. my Demon board died and the ECU went into limp mode. similar symptoms but no response to slapping. :)
 

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ed7
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cel will always stay on when you jump the connector...i should blink when you have a cel...

Did you tried connecting the ecu to the other car? Do you have a ob0-obd1 conversion or something?

By connecting it to the other car we should know is it ecu or the harness?
 

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Formally D_Tuned
97 civic HX
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If you get fed up with it send it my way, I like a challenge.

Really though, I know it seems obvious but really check the lytic caps, take hold of them and push them side to side and see if one of the legs easily break. I can name more than a few times where a ECU would do strange things or just act dead and look completely fine but one of the cap's legs had corroded away at the very base of the cylinder body, nearly impossible to see while attached to the board.

I now make it a habit of checking all lytic caps with this method on all ecus that touch my hands.
 

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another way to tell if the caps are bad is smell the board, if they are leaking it will smell like rotten eggs. thats the acid escaping from the caps, falling on to the very soft and fragile pcb board.

check for cold solder joints at the pins where they intercept the board.
 

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the ECU side pins are usually alright. the ones in the plugs can be painful though. when they get misshapen, etc. they dont make good contact with the pins anymore. I learnt this the hard way.
 
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