Changed ECU now runs bad.

Message

Reeve · #1 Post by **Reeve** » Mon Jun 14, 2010 1:57 am

A while back I bought an extra 1000 ECU to replace my ECU that got damaged when I shorted the fuel pump. My ECU still ran great it just had the fuel pump hot wired to run constant with a quick disconnect. Two days ago I fired it up and it ran just like normal for a couple minutes. Today I changed out the ECU and put the fuel pump wires back to stock. It fired right up and had a very high idle. I let it idle for a couple minutes and then the idle came down some and it developed a miss. I revved it a couple times ( not too high ) and tyhen it sputtered and died. I got it to start back up but it still had the miss and then died again. I changed the ECU and fuel pump wires back to the original way I had it and it still has the miss and dies after a few seconds. I know it has good fuel flow and I didn't change anything else. Any ideas? I don't know what could be the problem it ran for a couple minutes with no load and now it runs like crap with all the same stuff as it had when it ran fine a couple days ago.

proflow · #2 Post by **proflow** » Mon Jun 14, 2010 2:19 am

Plug is trying to die.
Swap it out & if you have means of doing a throttle cal. do it.

Good luck----Proflow

speedracer · #3 Post by **speedracer** » Mon Jun 14, 2010 8:42 pm

Is the idle high then low then high and low again? Will it just die on its own while at idle?

Reeve · #4 Post by **Reeve** » Tue Jun 15, 2010 5:44 am

I can pull the plug and have a look at it. It only ran for a couple minutes. I don't have any way of doing the throttle cal. Could changing the ECU out and back really mess up the throttle cal? It just had the high idle and when it came down to just above normal it started missing and then died. It now starts and misses and is hard to keep running. It will die within about 10-15 seconds of running

Canniboomer · #5 Post by **Canniboomer** » Tue Jun 15, 2010 4:38 pm

To complicate things;......I have confirmed here that 2 different ECU's, even with the exact same throttle voltages and flow settings, with the same fresh hex, and with the same map,...CAN behave very differently. If you are just swapping ECU's, each should be throttle-calibrated the same, and go from there.

If your issue started after a quick high revv, you might check for a partially spun flywheel.

Reeve · #6 Post by **Reeve** » Wed Jun 16, 2010 1:03 am

It really didn't rev that high but It's easy and I will check for that. I don't plan on changing ECUs all the time I just wanted to see if the one I bought worked because We gave it a try on Glens speed before he found his problem and Glen said it didn't prime the fuel pump right. It worked fine priming the pump and started right up but the tune and or throttle cal were off. I just don't see how after swapping back it won't run right. I have it on the charger and will give it a full charge and then have another go at it.

speedracer · #7 Post by **speedracer** » Fri Jun 18, 2010 9:36 pm

Did you getting it running?Just curious what the outcome was.

Reeve · #8 Post by **Reeve** » Mon Jun 21, 2010 4:11 pm

I didn't get it figured out yet. Next up is checking the flywheel plug and changing out the fuel and filter.

MX Quad Dad · #9 Post by **MX Quad Dad** » Mon Jun 21, 2010 9:33 pm

I would definatly try changing the plug.

You said you fired it up and let it run for a couple minuits. I try not to fire mine up unless I intend to let it warmup completly, because I have heard of others fouling plug because of this.

Reeve · #10 Post by **Reeve** » Tue Jun 22, 2010 1:05 am

Well I have never had a problem before but my plan was to let it warm up it just died after a couple minutes all on it's own.