So my car has been driving rough (started as rough idle) and progressed into the engine misfiring while driving. I've replaced all the basic stuff (coils, plugs, cleaned egr, valve timing, motor mounts, replace iacv, checked gasket was not blocking egr ports - ect). Been at the shop for a week (private) and the mechanic has yet to find the problem. YES, egr ports were cleaned by me and the mechanic which interestingly enough took away the rough idle but the car still drives rough and flashes check engine as well as 7 codes p1399 & p300-306.

I've read that a possible issue may stem from the cars central computer.
I'm a computer science major and anything software related peaks a personal interest of mine. So what type of computer would have to be replaced? Also, is it possible to gain 3rd party or even dealer software via the internet to accomplish a do-it-yourself flash? Or do they keep that programming under tight lock and key?

Lastly, in your opinion, would most dealerships allow you to purchase a used computer given the tremendous cost new and just charge for installation and flash?

 

Our cars ECU is permanently flashed - unfortunately there is no way to edit the program as its stored permanently on the chips die and cannot be edited!


Later tomorrow Ill chime in with more details... Cheers.

 

You can try getting a used ECU from junk yards in person or internet.

 

or find the real problem
whats the compression like- how do the plugs look? any loss of coolant or rise in oil levels? air burped from rad system with heater on hot and cabin fan on high- doors open to vent heat!

Rare is the failure of an ecu- bad grounds will mess the car up big time, the battery ground wire comes loose inside its connector to the frame- that's BAD!!
Others wear out- the braided wires ones from body to engine - 5 of then iirc

If it runs bad and cant figure it out- resort to the basics!
Amazing how often just cleaning every single ground wire you can find fixes many problems
Whats the voltage on battery now? and when running?
Battery itself tested at parts store? with the big machine= not the handheld pos
Weak batt will cause probs beyond belief- car runs off the batt and supported by the alt which constantly recharges the battery
AC.Alt belt tensioner working right?

 

Honda HDS 3 015 020 Software Latest Version Him GNA600 MVCI Ecurewrite | eBay

 

 

thats just a tiny eeprom that only holds your key info... the actual programming for the ECU is inside the big ASIC. there is discussion on honda tech about this


https://www.hondata.com/index.html

 

Our ECUs can NOT be rewritten, flashed etc..

 

Has your mechanic checked fuel injectors, and checked compression?

 

Compression is good. As for the injectors, they appear to be good but I've read testing isn't 100% with them unless you do it right, looking for leaks. I just changed my battery to a new optima redtop and I'm going to add a universal ground wire to be certain it's grounded. I also bought a egr valve today and threw it on but the problem persists. It's going to the dealer tomorrow : ( Private mechanic gave up and even took it to 3 mechanics in the area - all stumped.

I've read in other forums it could be a fuel delivery issue (ie bad fuel pump, clogged filter) but that's usually not mentioned on here. I've done everything possible so I'm making it the dealers problem. My hope is that they'll find a single bad injector vs me simply replacing them all. I've pretty much done all basic repairs to solve the p300-306 & 1399 misfires and have it narrowed down to to a fuel delivery issue or ecu - dealer don't rape me

If it is the ecu - should I buy one online for $40 and have them flash? Or buy with with the key and ignition where no flash is required? The ecu+key+ignition for for about $200, yet I wonder if my existing viper remote start would require reprogramming regardless.

 

Just desolder the two EEPROMS that hold the immobilizer data and move them over to the new ECU. Thats what stores your key and mileage data. There are a lot of videos on it and its common across many Hondas if you plan to swap ECUs. I don't quite understand your question.

 

Knice, you mentioned valve timing, but not valve adjustment. The exhaust valves tend to get tighter, to the point of causing misfires, without any other symptoms. Has anyone adjusted the valves? You can't tell by listening, as honda recommends.

 

So i used 3rd party ignition coils (all new) and the dealer is saying they're the problem. Even though they worked for 3k miles, recommends replacing with all oem. Tested with used coils and he said it drives fine.

I'm going to buy them and put them on myself but this could be a very costly lesson on buying 3rd party parts if they're right. They also state my rough idle is coming from a broken front mount. Stating "it's too hard" yet I thought that was typical of a poly mount vs stock.

 

They want $700 to replace the coils lmao. I went on automd to get a labor estimate and it says 3 hours bahahah. I did the plugs and coils myself in under an hour with little to no repair experience. What a crock. Ended up ordering 6 new oem coils for $250 and will rinse, wash, and repeat. Man i sware if they're guessing and i do this for no reason, ughh!

 

I would've had them put the OEM coils in and go for a drive with the tech in the car. If they say 'drives fine' who knows what that really means?

BTW nice to hear you're a CS Major - I am as well.