New 420R w/ RBTB - "sticky" throttle

[savagete2860]

Hi everyone, long time lurker new 7 owner here. I will make an intro post soon, but I figured this was as good as time as any to dip my toes into the usa7s community pool.

 

I ordered a 420R kit with roller barrel throttle bodies through Rocky Mountain Caterham and had them assemble the car. I took delivery of it earlier this month and it has been great up until a few days ago. For some reason, the throttle started "sticking". For example, if I am in gear with the throttle opened ~10% to maintain cruising speed, let off the gas, it will be like I am still pressing the accelerator and I will not slow down. If I put the car in neutral or press in the clutch, the RPMs will rise to 3-6k rpm rather than settle into idle. Giving it a quick jab or two of throttle seems to correct things (or make them worse until jabbed again) but it will just happen again to the point where its probably not that safe to drive.

 

It's also seems like the barrels don’t want to go back to their idle position. Also - maybe related, maybe not, the car does not always start which is also a new behavior. I have had about 5 cold starts just crank with no signs of life until hitting the battery cut off switch off and back on at which point it just starts.

 

I looked at the throttle pedal and it and the cable appear normal to me. The pedal seems to always return to it's starting position and when the throttle sticks there is no play in the pedal to move it. This leads me to believe the issue is at the RBTB end of the throttle cable. I pulled the filter and back plate off and notice i can use my hand to close the barrels further than they normally would be. If the throttle is actuated again, the barrels never return to what I imagine should be their resting idle position. Below is a video of what I am talking about. So my assumption, which very well could be incorrect, is that because there s a kind of dead space between the lowest opening and where the cable start to get tight to open the throttle and it seems like the barrels can get randomly stuck at any position in that dead space.

 

Any ideas of what to look at or do next?

 

 

 

[KnifeySpoony]

100% not right, definitely don't drive it. Something is clearly interfering with the barrel or cable movement. If you're not comfortable working on the car, have your dealer look at it. If you are,  I would disconnect the cable from the barrels- see if they open and close freely. The spring on the barrels is strong; when I let off the throttle, the barrels snap shut and the stop on the barrels bangs loudly against the stop screw. If the barrels move fine, then the issue is with the cable. It's possible something is assembled incorrectly, but can't tell from the video. 

[savagete2860]

Thanks @KnifeySpoony. I don't mind working on the car but I stopped short of removing the barrels themselves. Are there any tune implications to removing the barrel completely? My only concern is I don't have a way to check/set tps voltage and Id be worried I might change something there.

 

I don't believe it is the throttle cable itself - adding and picking up slack didnt change the behavior and its routed in a way that wouldnt interfere or be interfered with by anything else that I can tell.

 

I took another look and I don't really know how I missed it, but there is evidence of the return spring on the right barrel making contact with the adjustment bolt on that side. Is that bolt the full throttle stop adjustment? I think that is my smoking gun for the binding.

 

Edit: adjusted this and that seems to solve the issue when manually testing. However now WOT isn’t actually fully opened, it overshoots just slightly. Not a big deal while I’m breaking the car in though.

 

Edit on the edit: Still an issue with the WOT screw backed out a good bit to not touch the spring

 

Edited July 13 by savagete2860

[KnifeySpoony]

No need to take the intake off. Just make sure the open and close stops are properly set and working properly. Sounds like the WOT stop needs to be adjusted. Super simple. The tps adjustment is only for idle voltage. So hopefully that's ok. You can check with a multimeter. 

[savagete2860]

The WOT stop was adjusted correctly but the screw was making contact with the spring so I backed it off for testing. Seemed to help a little at least from larger opening to quickly letting off the throttle, but re-assembling  quickly showed it did not fix the problem. Car started and was idling, then i gave a very small blip of throttle and RPMs raised and never came back down.

 

Considering the front right screw was a stop for full throttle, I am guessing the rear facing adjuster screw on the left is for idle. Other threads indicate this is to be used to adjust the opening to 6mm via a dowel/drill bit/blank. That sound right? This adjustment would set the lowest the throttle should close - which seems to be set correctly again - but I can't see if if its interfering with the return spring, like the WOT stop.

 

Fact check me here. I have been ignoring the throttle cable itself because when I took the backing plate off, I manually moved the barrels to WOT position with my fingers and released to simulate closing the throttle, and the barrels got stuck and there was slack in the cable. The cable should only be under tension when opening the throttle, right? Its pulling the throttle open but the return springs on the barrels are what should be working against the cable tension to close. So in theory the throttle cable, unless getting in the way of operation, should not be relevant to my issue.

 

 

 

 

[savagete2860]

I figured out whats causing the issue - for sure this time. It is indeed the right roller barrel return spring. For some reason, the spring shifts when operating the throttle and binds between the roller barrel and the WOT stop. I validated this using a screw driver.

 

How is this spring is meant to stay in place?

 

 

 

Edited July 16 by savagete2860

[savagete2860]

Still scratching my head on this. Waiting to hear back from Caterham to see what they say as this is a part assembled and installed form the factory.

 

I saw a few photos from other owners where the right spring looks as though it is supposed to be more towards the rear of the car, so maybe how the spring is moving is correct but the stop just need filed down or something. Its peculiar that this whole setup worked from for a good bit and then started to bind. Im wondering if the coating on the spring slowly wearing away from contact increased the friction between the spring and the stop. I really have no idea.

 

If anyone with RBTBs can post a few photos of the return springs or a video if their operation that would be hugely helpful to have a reference and just validate mine looks correct or incorrectly installed.

 

I will be sure to post any updates as they come.

 

[KnifeySpoony]

I can try to take a pic/vid but I think with the trumpets/backing plate on will be hard to see anything (and they are annoying to take off/on, sorry). Given that you've already taken the trumpets off, I would just take the intakes off and see if each side is operating correctly on their own, and if so, reinstall them. The mechanism of each side has to interlock correctly (under tension which makes it challenging) during installation. Also have to make sure the gaskets don't dislodge from their grooves during installation. If the spring is still binding, then you may be correct that there is a flaw with the intake itself and may need replacing/fixing. 

[savagete2860]

Thanks - any I totally understand on not wanting to take the backing plate off, it is indeed annoying as you stated lol. Really I am just curious if the return springs favor the one side or the other on a car that has working RBs though and if they have any side to side movement with throttle application.

Edited July 16 by savagete2860

[savagete2860]

Taking off the RBs and I am a little stuck. There are 5 studs from the block that secure the rollers via 10mm nuts. I have all 3 bottom nuts removed and the top two undone as much as they can be. At this point I would expect the intakes to come off, but they do not budge. Is there a trick to this?

 

Also the install instructions from the csr260 manual says 

Quote

Note: if the barrel throttles have to be removed from the engine, always remove the TPS first,
otherwise it will result in the TPS being damaged

 

Do I need to remove the TPS? It seems like its just mounted to the side. Is the manual referring to the actual "barrel" that rotates inside of the housing which I am not touching?

Edited July 16 by savagete2860

[KnifeySpoony]

It should pop off. And yes you want to remove the tps because when the barrels come off, they will rotate beyond their (and the tps's) normal rotation range. 

[savagete2860]

Dang.. I ended up getting it off before seeing your response @KnifeySpoony and kept the TPS on thinking it couldn't possibly need to come off. I don't know if that did indeed damage the TPS or not but I will probably try to get a spare just in case. I just got done putting it all back together. Its dumping rain but hopefully tomorrow i can fire it up again and test it out. If the TPS is damaged, what would some tell-tale signs be? Would that throw a light or just cause drivablity issues?

 

Regarding the initial sticking issue, I am pretty confident its now fixed. I took the RBs off and loosened the bolt that holds the return spring to the housing which immediately stopped the sticking. Tightening it again and the sticking came back. With the bolt loose I then tried to position the throttle openings to around where idle is and tightened the spring screw. With that adjustment it seems totally normal again. I put it back on the car, attached and adjusted the throttle cable. With the car not running, I couldn't get it to stick and felt, looked, and sounded normal (metal snap). Before I put the backing plate, trumpets, and filter back on it did start the car - it fired up and idled fine (no revs since the filter wasn't on - and also i accidentally left the TPS unplugged). I am hoping the sticking throttle is now a thing of the past and fingers crossed my TPS is okay too.

Edited July 17 by savagete2860

[KnifeySpoony]

Glad you got it sorted. Hopefully the spring on the barrel wasn't strong enough to damage the TPS. You should check the idle voltage IMO. I would get set up to do that anyway, as I have seen the voltage drift and need adjusting, and had a TPS go bad. 

Edited July 17 by KnifeySpoony

[savagete2860]

I just went to take if for drive. Before I pulled out of the garage I tested modulating the throttle with the car running. Results: I must have messed something up. I only tested very light throttle to slowly raise the RPMs and it shuts power down quickly. Guessing this is related to TPS. I do not have easimap - how/where can I check the voltage for the TPS with a multimeter? If the voltage is high/low, how is it adjusted - rotating the TPS?

 

I am guessing easimap and a cable is something I should buy.

 

Here is a video of the hesitation.
https://imgur.com/a/twUGzIC

 

[sltous]

I found the easiest thing to do was to depin the TPS connector and measure between the center signal cable and any chassis ground.

 

Eventually you're going to end up needing an Easimap cable in my opinion.

 

I've attached the setup instructions that Josh at Rocky Mountain Caterham sent me.

 

WRNOT 608 - Roller Barrel Setup Ford Duratec Engine.pdf

[KnifeySpoony]

Measuring TPS voltage on back of the connector is possible but annoying. I advise getting an easimap adapter to make it easier. Re: your car's behavior - it sounds like the TPS is indeed not working. I know from experience that the car will idle fine with the TPS unplugged but will bog/die if the throttle is opened. Sounds similar to your behavior. 

[savagete2860]

Easimap setup is on the list of things to buy. So is a de-pinning tool, air flow meter, and a 6mm rod.

 

I de-pinned the TPS connector as @sltous showed- voltage was 4.58v at idle, which while not 4.62v, I can't imagine thats enough to really throw off the fueling on very light low rpm revs. I have been wrong before in this thread though so who knows. I did however open the throttle a little with my thumb on the throttle cable attachment behind the filter backing plate and the voltage on the middle pin never changed. Is that confirmed bad TPS?

 

Is the TPS something I can pick up from a local autoparts store/ford/mazda dealer or does it need to come from Caterham?

[KnifeySpoony]

Even very small difference in idle voltage make a big difference (I learned the hard way).  However at 4.58 it should still rev, but could have fueling issues. My guess is your TPS is bad. You can pick one up at your local Ford parts counter. 

[savagete2860]

Just FYI for anyone looking and because Caterham was kind enough to scratch off all the logos and part numbers, the Ford part for a TPS replacement is ys4z9b989bb. Unfortunately it is considered "obsolete" by Ford and as of typing this, there only select parts departments that have them in stock. None are really close to me so I think I am rolling the dice on a Duralast version from AutoZone to see if if fixes the car and I will plan to get a genuine Ford part down the road.

 

https://www.autozone.com/engine-management/throttle-position-sensor-tps/p/duralast-throttle-position-sensor-tps-tps274/364464_0_0

 

https://shop.advanceautoparts.com/p/carquest-premium-throttle-position-sensor-ecc1036/12424329-P

 

I will post an update when its back on the car.

[savagete2860]

Ended up buying both TPS's I linked above. The autozone one is a bue-ish color and seems very cheap. It was so cheap and blue I drove to an advanceauto to pick up the other which seems better made and is black like the OE. Popped it on the car, adjusted voltage to 4.62v and everything is well in the world again. Thanks @KnifeySpoony and @sltous for all of your hand holding. Not only do I now have a working car but I learned what I am pretty sure is everything I would ever need to know about roller barrel throttle bodies on these cars.