5.7 Hemi limp mode, help needed! 1968 Charger

[Qtti]

Hi everyone!
I have 1968 Charger with 5.7 truck Hemi (2006) and 545RFE transmission. It has factory ECM with drive-by-wire gas pedal and S&P wiring harness. My problem is that car goes to limp mode. If I start 10 times, it goes to limp mode probably 7 times. I have new gas pedal, new throttle body (BBK 85mm), and I just bought new ECM from Hot Wire Auto. Still same issues.. What could cause this? Crank sensor? Cam sensor? Here are the codes I´m getting: U0155, P0480, P0443, P0499, P0073, P0038, P0058. When my scanner is plugged in and car running on normal mode, I can see that ignition timing varies from -5 to +15. If I over-crank it when starting, I feel that that way car more likely starts on normal mode. ECM is getting 10.x volts when cranking.

Can someone please help, I´m getting desperate and nuts here.. What should I check next?

 

[Sixpactogo]

What are you using for a speedometer? I have heard from Chris at Hotwire that there have been a few instances of your problem arising when you are using an aftermarket electronic speedo. He mentioned to me that sometimes the computer does not like the communication between the transmission and the electronic speedo and will send the transmission into limp mode. I have the GPS speedo in my 68 Charger with the 545RFE and have not had the limp mode issue but my GPS speedo does not get a good signal and or gets some interference from somewhere. I am thinking of trying the electronic speedo in mine but have not yet done so.
Also, another thing comes to mind. Chris told me another problem with the Gen 3 Hemi is that it does not like the vintage ignition switch that has Ignition 1 and Ignition 2 configuration. I was able to get mine to work but it didn't run just right. I ended up adding a push button start button and just use the ignition switch for on / off. It seems to help. Not sure if either is your problem but it is a place to start.

 

[Qtti]

Thank you for your advises! I´m using Dakota Digital MHX-68D-CHG metric instruments. When we have had our scanner plugged in, OBD to speedo/other gauges has been disconnected, and still car has gone to limp mode. Should we disconnect power from speedo also to check if it interferes? Also I think that I´ll add push button start button at first and see if it helps. I´ll send results when it´s done, this is a good place to start.

 

[Sixpactogo]

If you had the green wire from the transmission disconnected from the speedo, I would have thought that should have been enough unless the computer gets conflicting information from somewhere else. It sounds like you have the same luck as I do with these gremlins. I went with the GPS speedo because of what I was told about the limp mode issue with the electronic speedo. I think I am the only one that is having trouble with making the GPS unit work. I have tried two different speedometers and two different antennas with the same results. My speedo is intermittent and only registers about half of the time. I really don't need a speedometer but my wife won't drive the car without it. Maybe that is a good thing. When you do a shut down and restart, does your transmission work properly for a time and then go into limp mode? Or does it not shift at all? I think I will call Chris again tomorrow and quiz him again. I will let you know if he has any new leadership.

 

[Qtti]

Actually my speedo gets the signal from the crank sensor installed to drive shaft. I don't have GPS. I'm sorry if I wasn't clear enough. Other data goes via OBD. When car goes into limp mode, engine doesn't respond to gas pedal and it idles 1200-1300 rpm sounding unhealthy, transmission works properly but if I try to drive it, I can't push the brake pedal hard enough to stop it. It's dangerous, car just pushes and pushes forward. I also sent an email to Chris but if you can call him, it'd be great!

 

[Qtti]

And we have already built relay/hot wire system (actually a professional car electrician made it) from ignition to ecm. ECM is getting continuous power (10.x Volts when starting) also when starting the engine. My battery is new, Optima Yellow Top, but kind of small, only 48Ah, because of limited space in engine compartment. Feel free to ask more about my setup if I'm not clear enough.

 

[Sixpactogo]

Ok, Sorry. I knew you didn't have the GPS speedo. I just assumed you were using the green wire from the wiring harness provided by Hotwire. It provides the data from the transmission speed sensor to the Speedometer. It sounds like you have a way different set-up than what I was thinking. From what I think you are saying, it is not the transmission that is going into limp mode but the engine goes unresponsive instead. Probably none of my input can help you any. I am not privy to any of the codes you are getting but I would think the ECM will need at least 12+ volts to operate properly. I have my battery mounted in the trunk. It is an 850 Cold cranking Amp battery.
I'm not saying your battery is the problem but it seems too small to me. If you get your info to Chris at Hotwire, Hopefully he can shed some light on your problem.

 

[Qtti]

Yes, my engine goes unresponsive and for that reason I'm not sure if my transmission works or not when it goes into limp mode.. I have tried only first gear when engine goes into limp mode. When it starts normally, everything works fine until next shut down. It never goes into limp mode while I'm driving, only on start ups. My wiring harness is from Street&Performance, but HotWireAuto sells them nowadays. I bought my car a year ago already tech swapped, and I've been working with the car to improve it since.. Previous owner installed the speed sensor and we installed the extra wiring harness from ignition to ECM, otherwise my setup is quite "stock": 2006 truck 5.7 hemi+545RFE, Kilduff horseshoe shifter, S&P wiring harness, drive-by-wire gas pedal (new), factory Chrysler ECM (modified by HotWireAuto), BBK 85mm throttle body (new), K&N cold air intake, Dakota Digital instruments with OBD, Ridetech's computer/height sensors/air suspension/blue tooth operated/4-link rear/front tubular control arms, SSBC disc power brakes on all wheels, race tank with small electric pump near the tank and Edelbrock's high pressure pump in engine compartment, Optima Yellow Top 48Ah battery. That's pretty much it.

I would highly appreciate any help from anybody. What can cause my engine unresponsive behaviour?

 

[Qtti]

Sixpactogo, I'll install a bigger battery and try. I hope Chris or someone could help me. This car is driving me nuts

 

[Sixpactogo]

Sixpactogo, I'll install a bigger battery and try. I hope Chris or someone could help me. This car is driving me nuts

Before you deal with a larger battery, I would try adding the push button start. I know it sounds silly and you would think if it starts, it should run the same every time but I noticed that mine did not. Sometimes it would start and run great and the next time it would be limping and idling rough. I tied my ignition 1 & 2 together so it would not drop continuity between start and run but for some reason, it seems to run better with just turning the ignition to run and using the push button to start. Hopefully it will cure your problem but these electrical problems can be a nightmare. Good Luck!

 

[kb67mopar]

Try cleaning the throttle body. I have had two instances in my truck on a cold day where this sort of thing happened and normally it would flash a light on the dash. The throttle body could be dirty or damaged. I really don't think its related to voltage during cranking. I think the ECM can tolerate down to 9 Volts or something near that. I would recommend using a push button to start it though. I couldn't even get mine to crank with the goofy low voltage off the factory ignition switch. I had to use a push button.

 

[Qtti]

Kb67mopar, my tb is brand new.
Chris from Hotwire Auto replied my email today, and I was advised to bypass the ignition switch and do some re-wiring. I'll also add the push button start. I'll let you know if this helps.. I must say that Hotwire Auto's customer service is very very good!

 

[5.7 hemi]

Tie ignition 1 and 2 together, as you need 12 volts at run and crank.

 

[Qtti]

We added the push button start yesterday. I started the car six times, and every time it started on normal mode. So problem solved! I´m so happy! Here are the advises Chris from Hotwire Auto sent me:
- You need to leave the heavy red wire attached to Battery(+) 12v constant power.
- You will leave the pink wire on the ignition switch, connected to the “on” position. No need to tie ignition 1 and 2 together.
- Take the yellow wire off the ignition switch and put it to one side of a momentary push button.
- The other side of the push button gets 12v. (keyed or battery doesn’t matter)

So special thanks to Chris from Hotwire Auto, superb customer service! And thank you also for advising me, I really appreciate!

 

[Sixpactogo]

Good news! Glad you got it solved. Now go celebrate with a smokey burn-out

 

[Qtti]

Yeah