Limp Mode Up Hills after ECU & Exhaust

[Challengrtj]

I’ve had this issue a while but have decided to post now to inform others and to get opinions on solutions. PC Challenger automatic with an ECU remap and 3 inch exhaust. I also have the EGR blanked off. Remap was done by Power Torque in Brisbane shortly after brand new as was EGR blank plate. No issues at all until I had the full 3” exhaust fitted about 2 years later. Had about a 10% improvement in power and torque from the remap (big improvement in drive ability), but the exhaust made a bigger difference to performance. Rough guess about 30% over standard. Awesome really.

But with after remap and exhaust had an issue when towing my 2 tonne van. All good under high load, but at the crest of the hill when backing off accelerator car would go into limp mode. Would have to pull over and let all the vehicles I just passed go around. Turbo over booster code was the cause. Took it back to Power Torque and they adjusted tune parameters and the problems improved a lot, although performance was slightly blunted.

I have mostly done outback travel so not a lot of hills, but last few trips went to Victoria high country and presently in South Australia. A lot steep, undulating hills so limp mode issue is back with a vengeance. It would seem that a remap and exhaust pushes the limits of the boost controller and cause san over booster condition on a trailing throttle, but still higher load conditions. I did check the forum but nothing similar, although it seems like 3 inch exhaust is overkill.

I really need to have it sorted and I’m unsure what to do next? It mainly happens when cruise is on. If I control the throttle manually and avoid bigger inputs and rapidly backing of the throttle it tends not to do it. Any one had anything similar or have any suggestions? I will check the hoses around the turbo and MAF sensor. One thing that has changed (other than more undulating steep hills) is that I had a catch can fitted at 90,000km as there was some oil in the inlet even though EGR disabled.

Any comments gratefully received.

[old Jack]

Is the check engine light coming ON?
Are you using "Drive" or which gear in sport mode?
Does the gear display on the dash "flash"?

OJ.

EDIT;
Have a read of this thread when you have some spare time!

https://www2.pajeroclub.com.au/forum/showthread.php?t=36892

[challenger121]

I have also heard the 3 inch exhaust is too big and its better to go 2.5 to 2.75 inch exhaust.
Beaudesert exhausts make a 2.75 inch for the challenger and below is a statement from their website:

Be careful! Having an exhaust system too large for the motor can have the opposite effect! We have had some customers come back to us with aftermarket exhausts that are too big for the motor and in turn it has given them more turbo lag and less overall power gains. On some motors if the exhaust is too big you can run into some problems including over boosting or even boost spike of the turbo which will throw you into limp mode. This can be extremely dangerous if you are towing a caravan or trailer. This can happen from the turbo trying to spin too hard and fast, the ECU recognises this and can throw the car into limp mode.

Jono

[Challengrtj]

Is the check engine light coming ON?
Are you using "Drive" or which gear in sport mode?
Does the gear display on the dash "flash"?

OJ.

EDIT;
Have a read of this thread when you have some spare time!
https://www2.pajeroclub.com.au/forum...ad.php?t=36892

The problem can occur in both drive mode and in sport mode. When going up hills, even if using cruise, I manually change into 4th before the hill steepens because it then locks up in 4th and climbs the hill with less strain. No the gear selector does not flash. I can’t be 100% sure but I think I would have noticed it if I did (I’ll be sure to look next time). The limp mode issue has occurred at high speed on relatively flat roads, e.g. passing using 3/4 throttle and then backing off to merge back in as well as on undulating hills, while in lower gears. What causes the issue to going from a open throttle to a trailing throttle under moderate load. I can climb the Toowoomba range out of Brisbane that is very steep and long without issue because it involves only small amount of trailing throttle. If it was a transmission issue I think the range would cause it, but it does not. Never had an issue when not towing. I reset the ecu with a king chrome elcheapo tool. It does not record an error code, but when I use the torque app the turbo error displays.

[Challengrtj]

I have also heard the 3 inch exhaust is too big and its better to go 2.5 to 2.75 inch exhaust.
Beaudesert exhausts make a 2.75 inch for the challenger and below is a statement from their website:

Be careful! Having an exhaust system too large for the motor can have the opposite effect! We have had some customers come back to us with aftermarket exhausts that are too big for the motor and in turn it has given them more turbo lag and less overall power gains. On some motors if the exhaust is too big you can run into some problems including over boosting or even boost spike of the turbo which will throw you into limp mode. This can be extremely dangerous if you are towing a caravan or trailer. This can happen from the turbo trying to spin too hard and fast, the ECU recognises this and can throw the car into limp mode.

Jono

Yes it would appear that the exhaust is the issue. I’ve heard the turbos on the Challenger run fairly high boost but the ecu remap guy said they don’t touch the boost and didn’t have an issue until the exhaust. Quite a few people do offer 3 inch systems for challengers though, even ones that do remaps like Roo systems. I’m going to try to administrative controls to try and manage the isssue. I’m not a hoon driver anyway but a can try using lighter throttle inputs up hills. I think the problem has gotten worse with age so I’ll look into if it’s a sensor too.

[old Jack]

To prove it is an exhaust back pressure, turbo over boost problem, rather than change the exhaust just get 2 tail pipe reducers made to reduce the diameter at the exhaust outlet.

A piece of 2.75" exhaust pipe expanded out so it will slip over the 3" and clamp into place.
A piece of 2.5" exhaust pipe expanded out so it will slip over the 2.75" pipe and clamp into place.

If either of these solve the problem then by squashing the exhaust pipe down so the outlet changes from circular to oval will reduce the cross sectional area.
If you squash down to about 47mm in height will give you roughly a 2.75" diameter exhaust.


OJ.

[PeePee]

I have also heard the 3 inch exhaust is too big and its better to go 2.5 to 2.75 inch exhaust.
Beaudesert exhausts make a 2.75 inch for the challenger and below is a statement from their website:

Be careful! Having an exhaust system too large for the motor can have the opposite effect! We have had some customers come back to us with aftermarket exhausts that are too big for the motor and in turn it has given them more turbo lag and less overall power gains. On some motors if the exhaust is too big you can run into some problems including over boosting or even boost spike of the turbo which will throw you into limp mode. This can be extremely dangerous if you are towing a caravan or trailer. This can happen from the turbo trying to spin too hard and fast, the ECU recognises this and can throw the car into limp mode.

Jono

I had mine remapped at Power Torque a couple of years ago and have the 2.75 exhaust from Beaudesert, works well with no issues at all. I also have the auto mate on mine, that has improved the torque converter issues greatly.

[Challengrtj]

I had mine remapped at Power Torque a couple of years ago and have the 2.75 exhaust from Beaudesert, works well with no issues at all. I also have the auto mate on mine, that has improved the torque converter issues greatly.

That’s interesting. Do you do any heavy towing like I do? I would have to say that I wouldn’t know I had a problem unless I was towing. For example have done trips heavily loaded like the Simpson Desert with no issues. But when I have the car loaded along with the van then it strikes.

[old Jack]

Just another thought or 2.
1. It could be the ECU Map has changed the factory throttle buffering gradient on a trailing throttle.
2. It could also be the EGR plate, maybe it causing a feedback error when under high loads then trailing throttle. Easily checked by removing the EGR blank, if this solves the issue then you could try an EGR electronic resistor mod to see if you still had the problem.

OJ.

[Challengrtj]

That’s some lateral thinking for determining if the exhaust helps. The high flow cat is stainless as is the tail pipe, which has a downward bend. The middle section is aluminised steel. I might get an exhaust shop to make reducers and replace the middle part of the exhaust with say 2.5”. Too much mucking around to try and modify the stainless end. I did read that link and before I PM you to ask about the Auto Mate. I think having greater efficiency for climbing would help reduce the throttle inputs but I feel that is probably treating a symptom rather than the cause. I’ll probably purchase the lockup mate as I don’t use the Challenger much except for towing and I am well practiced at using sport mode - so easy with the paddle shifters.

[Challengrtj]

I installed the blanking plate my self as soon as I got it home as was aware of inlet blocking issues. A few months later when I got the tune I think they turned off the EGR system at ECU level. As I said I did take it back to Power Torque and whatever they did helped a lot. I’ll research throttle buffering but I’m presuming they probably looked at such issues. I’ll do something about the exhaust as I think that’s the low hanging fruit. Everything was okay before that and the turbo over boosting is not something that can be attenuated by the ECU parameters. I don’t won’t to rob too much performance from the engine though. That exhaust really made a difference to the performance.

[old Jack]

You will be surprised at the difference using Lockup Mate has on the drivability of the auto Challenger. I use the manual mode of Auto Mate in hilly terrain, off the bitumen and when off road. The auto Auto Mate mode is used around the city, suburbs and when touring on flat or undulating roads.

Please keep us posted on the limp mode issue on trailing throttle.

OJ.

[PeePee]

That’s interesting. Do you do any heavy towing like I do? I would have to say that I wouldn’t know I had a problem unless I was towing. For example have done trips heavily loaded like the Simpson Desert with no issues. But when I have the car loaded along with the van then it strikes.

No heavy towing for me sorry, I only tow a trailer these days. I would not attempt to tow anything at 2 tonnes or higher with the challenger.