Cyls 3 and 4 are not firing in my 1991 Prelude SI.

I have verified that they both are getting spark. I have tested the injectors per the Honda shop manual, verified that they are getting battery voltage, verified the connection between the injectors and the ECU, verified that there are no opens in the wiring harness that plugs into the ECU. I also swapped the two injectors with the #1 and #2 cyls, same prob. At this point the shop manual says to replace the ECU with a known good and retest. Before I go out and junkyard an ECU I wanted to see if any of you guys had some ideas on what else to check.

 

hang on man before you head for the junk yard i assume you have a volt meter check your injector resistor in accordance your pub you shouldn't have full battery voltage at your injectors. if you do thats bad and your injectors probably suffered for it. check the resistance of the injector if it exceeds 2.5 ohms and the rest are lower than 2.5 replace faulty injectors and injector resistor. here's some pics of what im talkin about...[IMG][/IMG][IMG][/IMG][IMG][/IMG]sorry i obviously haven't yet figured out how to upload pics.


Modified by stpierredm at 1:52 PM 6/18/2006

 

Yeah I checked the resistance of each injector and all are the same, just under 2.5 ohms. I also checked the injector resistor like the manual said and it checked out too. I don't remember how much voltage was at the injetors when I tested it, but it was normal according to the manual.

 

Did you do a compression test to make sure that cylinders 3 and 4 have compression.