Very interesting, you learn something new every day. This board is great.

I'll get to adjusting later on and report back.

On the "hard reset" I've seen posts about removing the terminals and touching together. Not necessary? Just remove and let sit for 15-20 minutes?

 

Just was in the garage this evening and doing my first shot at polishing the XJR, trying to get the 20 foot paint job down to 10, arm got tired so I figured I'd have a look at my throttle position and sure enough, I'm maxing out at 70.2%, consistently. Tomorrow I'll recheck the kickdown switch and then locate the cable adjustment and get it up in the mid to high 90's if I can. I've been thinking my butt dyno wasn't feeling 370 horsepower, judging by this I'm correct, I've probably yet to fel even close to 300. No wonder it won't smoke the tires from a dead stop without using the brakes.

 

Let me know how you get on. I haven't done mine yet, had a busy couple of days. Picked up my new x350 this morning, what a fantastic car. Spent the day cleaning that guy, but I'll get back to the R soon.

 

Cool, didn't know you made the commitment. Hope its a great commuter car for you!

 

Thank you, I hope so too. So far I love it. It's a 2006 XJ8 L in Liquid Silver over Black with only 41k miles. Definitely not as cool as the 308 XJR, but feels like a more usable daily than the 308.

 

Damn! Found that extra 100 horsepower I was missing.

So my cable deflection pre-adjustment was pretty significant, I'd put it at about 1/2" or so, which is a LOT on that tiny little run of cable. Left my OBD scanner showing live throttle data, snipped the ziptie and popped the adjuster out, went in 1/2 turn increments until I got it from 70.2% up to 98.2% at WOT and kickdown switch depressed. Shut everything down, new ziptie on and pulled the negative cable, touched it to the positive for 15 seconds and fixed a fresh cup of coffee. Let it sit for 15 minutes, reconnected and started the car. High idle at first but I didn't observe any of the wandering idle I kind of expected. Let it run for awhile at idle until it got to operating temp and checked the OBD data, idles at 640-ish rpm and 2.7% throttle.

Took it for a drive, I could tell it was different before I got out of my driveway. Got it noce and warmed up and then stood on the gas in normal mode at about 40mph, trans kicked down a gear or two and the car just WENT. Did a full throttle start in normal mode, car is noticably quicker in normal mode now than it was in sport mode from a dead stop in the same location before. Did a quick TCS off full throttle start in normal mode and was greeted with more tire spin in second gear than I ever got in first before the adjustment.

So I'll call this a success...my missing power was probably somewhere in the range of the difference between an XJ8 and an XJR. Can't wait to drive it a bit more now and get the feel for it. Great advice guys, many thanks.

87LC2, definitely do this, adjustment took me 15 minutes and another 30 to let it relearn the throttle setting, so maybe an hour including taking off the under hood covers and all that. Well worth it.

 

^ that's good to hear. Another successful tune up that doesn't cost anything.

The only downside about a fully functioning WOT is the gas mileage being directly inverse to grin factor...

Bottom line is a new to you car gets this along with servicing pretty much everything there's no record of.

 

Awesome! Can't wait to do mine, I should be able to get to it within the next couple of days.

 

Seems as though a check is order to see if the Duchess is slacking
off on me.

 

I just checked mine today….95% with the kick down switch mashed to the floor. If I interpret what I read in this thread, that’s probably fine? I haven’t noticed any performance issues, but I don’t drive it very hard, so I thought I would check it just for fun.

 

Yup, you're good.

I made the adjustment and reset the computer on my car today. Took longer to get the scanner hooked up and booted than to make the actual adjustment. For reference, I was at 52% with the kick down pressed, adjusted to 95% with kick down pressed. Can't wau to drive this thing, its going to be like a new car. Rain tonight so cars not going out, hopefully tomorrow.

Did not have to adjust the kick down, all of the slack was in the throttle cable. Pretty unbelieveable actually. I'll report back when I get it on the road.

 

Found the TPS reading at the bottom of the live data menu on my scanner and discovered I was at 62% at WOT. I checked my wife's car and that reads 80%, and that one's never been disturbed from factory settings. When I set up my engine (transplanted into a Mark 2) I set the cable adjustment so that it was just under tension with the spring loaded throttle mechanism against the idle stop (I'm assuming this is the motor that drives the throttle plate and interfaces with the ecu?). As I slowly adjusted the cable and put tension on the throttle (it would rotate off the stop), the TPS would show an increase at WOT. Along with this the idle would increase and never settle down, even after a hard reset. My current TPS reading at WOT is 77% and the beast is idling just under 3000 rpm. Wondering how long it takes the system to "learn" as I hate to leave it idling so high (probably 20 or 30 seconds - seemed an eternity). I'm wondering if my recent uncontrolled acceleration incident is perhaps related to this inability to learn? Or am I not giving the beast sufficient time after each adjustment to learn the new setting. Hope I'm explaining this clearly. Any thoughts much appreciated.

 

I can't speak to your acceleration issue, but I can tell you that after I adjusted my WOT setting I disconnected the battery negative cable, touched it to the positive for 15 seconds and then let it set disconnected for 15 minutes. Reconnected and started the car, my idle didn't go anywhere near 2k rpm, I'd put it just north of 1000, maybe as high as 1250, but I don't think for more than he few seconds of cold start. I didn't touch anything apart from reading the tach and watching rpm in my scanner, my idle did not do much wandering around, it basically acted like it was a regular cold start in my case.

Given runaway throttle in your car, I'd be looking at the TPS itself. I have an 07 Dodge Durango that periodically eats TPSes, but its behavior is the opposite...runs ok but stalls out, which I've assumed might be an intentional failure mode, but maybe I've just been lucky. Have you replaced the TPS in you car? Sorry, but I didn't follow the other thread.

 

TPS is the original. Fortunately the acceleration issue hasn't resurfaced in a few hundred miles of driving. One would think the default mode would be to idle vs WOT - wondering if the cruise control circuit is involved? The only code I got was 1229 - electronic control circuit.
I didn't wait the 15 minutes after the 15 second hard reset - will do that and see if it helps. Thanks.

 

Little skeptical of the 15 minute waiting period myself, but it can't hurt to try.

I see your other thread, I'll reply there instead of spamming up this one further.

 

Frustrated that I couldn't get close to WOT without creating a high idle, so I removed the kickdown actuator to see if the problem was mechanical. Sure enough the beast went right to 100% - turns out I simply wasn't getting full pedal travel. I can only get to 80% with the kickdown in its lowest position, so I'll have to cut down the bracket I fabricated for supporting its mounting post in the Mark 2. The beast was already alarmingly quick, so I'm anxious to see how it performs at full throttle vs the 62% I've been getting. Thanks to the folks who tried to assist on this.

 

Finally got the car out tonight. Started her up and she shot to 3k rpm (pretty sure there's a limiter in park) and settled down after 10 seconds or so to a perfectly smooth idle. As far as the results, sort of a good news bad news deal. Good news is that the car is an absolute beast! Also fixed my pedal position, was awkward having the brake pedal so high and floppy gas pedal is gone, everything is even now. The car just accelerates like mad now, feels fantastic. Only pulled it up to 4500 rpm or so and it pulled smooth and hard.

Bad news - pretty sure my secondary fuel pump is dead. With all of the extra power I didnt want to push the car too hard until I confirmed everything was good. When I got home I jumped the pins (30 & 87) on the seondary relay and nothing...primary works fine obviously. Glad I didn't push the car. Is there anything else I need to test to confirm, or is it dead? Funny, the car starts just fine on 2nd or 3rd crank and I've heard that a dead secondary pump will cause long cranking.

@Addicted2boost - You were right! You mentioned this a few months back when I got the car. Not sure if the secondary pump was dead then, but sure is now!

As far as pumps, anyone use the Delphi kits? Direct replacements and cheap - PN del38-k4014 Read about them in another thread and see they are direct replacements. Any other input appreciated, will hopefully get to this job within the next month or so, have a lot going on right now and in no rush. Just won't push the car past 3500 or so until I get it fixed.

 

I feel that I’m familiar enough with these cars that I like to at least give a heads up about known component issues to keep owners in the know about these cars. I myself am a Denso kinda guy so I’m going to recommend 9510008 for the pump and a Delphi FS0092 strainer from rockauto.com. Keep in mind that the short harness that comes with it needs to be fitted. I can’t recommend the Delphi pump because I’ve never used it before.

 

Odd I had that very same suspicion on my 2001 X308 AJ27 NA thinking the previous owner had some type of speed limiter value programmed into the ECU or some other limiter hack because I could never get over 109mph. But in my case, I could redline the first two gear shifts but not quickly.
After chasing a lot of rabbit holes and "typical" failure advice I finally did a full compression test and leak rate test.
That revealed all 32 valves were leaking badly and the engine could just not generate enough power to get over that speed.

I tore down the top end to find all 32 valves and seats very badly pitted from carbon fouling, like someone took a tiny ball peen hammer to both valve and seat surfaces. In reality tiny ***** of hardened carbon over time get caught when the valve is opening and closing and were creating the pitting, many linked together from the inside to the outside of the valve seat surfaces making a open path for gasses when closed.

I meticulously stripped and cleaned the heads, lapped in all 32 valves and checked each surface mating contact seal with machinist blue, painstakingly re-gapped all 32 valves, resealed all valve stems, cleaned the pistons and top end of the block to like new sparkling clean, reassembled the top end with all new gaskets and seals. On rechecking the compression I had a consistent 175 PSI +/- 1 PSI across all 8 cylinders, zero leak down with a small squirt of oil in each cylinder to lube the rings.

The driving and performance difference was like night and day changing an old car to a new car and for the first time since I purchased that car I could spin the wheels with Trac off, hit all redline shifts and MPH at published specs, and hit the electronic limiter of 168 mph on an open and traffic vacant road.

Too often we discount the mechanical parts correctly functioning of the engine for sensor issues, which all need to be considered in the big picture of troubleshooting.

Just my thoughts and experience.