redursidae

Thank you, Croc. No insult taken, and I appreciate verification on anything I post. I didn’t know understeer was the de facto behavior as this is the only Caterham I’ve pushed hard enough to find out, and I’m still learning how to dance with it. My expectation was that it would oversteer naturally and I would have to manage it. At Autocross I did a better job of balancing the weight, but didn’t do great every time and it showed. I’m no professional and still got much to learn. Yesterday I admittedly chucked it into a hair pin expecting Chapman’s hand to give me rotation. It’s good to know about the high speed understeer too, although that sounds like aerodynamics may be playing an effect too? Greatly appreciate you sharing your specs! Good to hear that you shim the rear as well. Are there a set of recommended shim kits? Could I bother you with sharing a picture of where you measure the ride height? I thought I measured it at the right place but every time I look I get more confused. I set it to 145mm front and 160mm rear with me in the seat, mainly because of oil pan clearance but it will be lower with 13s once I eventually do that.

Took the Cat to get an alignment today expecting it would be bad after raising it so much. It was kinda bad with -1.2* camber and 0.45* of toe-out up front, 5* caster. Rear was -1.5* camber and 0.1 toe-in. To help eliminate understeer I asked them to set the front to -2 camber, 0 toe. Went for a quick blat and it feels better, but it still understeers when pushed hard enough. I’m going to shim it to try and get 6 or 6.5 caster and try again. Next step might be trying to stiffen the rear roll bar but I would rather not because likely that the tires have some blame in this. At any rate, I’m loving this thing .

This is a common misconception about oxygen sensors and gauges. Oxygen sensors don't read AFR, they read Lambda. Lambda doesn't change with the type of fuel, and Lambda 1 is always stoichiometric regardless of fuel. The gauge converts the Lambda reading to AFR based on a user configurable setting which is a multiplier of stoich AFR * Lambda. By default this setting tends to be 14.7AFR = Lambda 1 for the gasoline scale we are used to. As a result, an engine idling with an AFR reading of 14.7 but running E85 doesn't actually have a 14.7:1 ratio in the exhaust, but instead 9.8:1 . The sensor is reading Lambda=1 (9.8:1 for E85), but the gauge has converted it to the gasoline scale. This of course changes if you modify the scale in your gauge. @Mudder The AEM X series gauges are good and reliable. Install the oxygen sensor behind the collector of your 4-1 header. It's also a good idea to wire the controller in such a way that it doesn't heat the sensor until the engine is running to prevent condensation from damaging the sensor.

Im not saying that this is the root cause of your issue, but the TPS calibration needs redone. The TPS voltage should typically be between 0.5V and 4.5V. Outside of that range it usually means a sensor or wiring fault. You should set the 0 point to the voltage seen with the engine idling and butterflies at the resting position (4.49V for your case). Similarly for the 100 point and linearly interpolate between the two. Changing this will of course change your fueling. I have seen cars where the TPS voltage changes between drives and that’s an indication of a failing sensor or counterfeit sensor. And regarding an IAC for idle control, I personally find it to be a must for a street car. I run one with my TWM manifold similarly to what you described. The simpler method is using a PWM actuated solenoid, but for this to work the TPS has to read below the threshold set in the map. If you post of pic of the solenoid I can tell you what kind it is.

Even in the single throttle cars? I would have expected the MBE to be a VE model at least, but nothing wrong with Alpha-N as long as it has the right compensations. I'm very interested in checking out a map if anyone has one to share. I took a read through the posts and I see what you mean about something beyond the map being the cause. I'm suspicious of the TPS and MAP readings from his screenshot. It's possible he doesn't have MAP if using pure Alpha-N, but the TPS is critical and should read 0% with the engine off. Of course, that's assuming it was set to 0% when the mapping was done, in which case would explain some of the richness. I know the MBE's use load site based axis, mapping volts instead of throttle percentages, but this Pectel seems to be percent based no?

I strongly suggest a modern ECU tuned with a VE model and at the very least short term PID control of fueling. Judging by your screenshot, the Pectel is injection time based and pure Alpha-N? That’ll be rough to get consistent. Also is your TPS always at 10%? Because that’s a problem considering that’s your main sensor

Understood, and thank you. Will inspect the grounds.

Good to know. One of the original tail lights was working intermittently before, so I will start looking around there. Any idea if missing reverse and fog lights might have something to do with this? Yep, I did. The car already had an LED relay, and I also tried JAL's relay to be sure.

Good news! The fuel has stayed in the tank since the Autocross, and what was dripping didn’t smell like fuel, instead some sort of glue or residue in the underside of the aluminum shelf. Since cleaning the shelf and the tank as best I could this hasn’t returned As far as overall fuel smell, it is much better. I only smell the breather doing its job when I slosh the tank on a spirited drive and it subsides after some cruising. Decided to do an LED swap with tail lights and indicators from Just Add Lightness, and headlights from Summit Racing. The headlights leave a little bit to be desired in their beam pattern but it’s decent. The tail lights are good and bright as needed. The indicators have not worked well so far, and cause all the lights to panic! With only one indicator on, all of the car's light flash, including the gauge lights. If I turn the lights on, then the buzzer is constantly on and the indicator bulb is lit. That’s a first. I tried disconnecting the tachometer to test the theory that the telltale could be the cause, but no dice, and not really sure where to go from here. This issue only happens with the LED indicators installed. Here is a video of the behavior with only the right indicator on: Another interesting new quirk is that while driving with the lights on I can hear the buzzer and see the indicator bulb light up intermittently as I hit bumps. This is making me think there is a bad ground somewhere.

It’s always best to find a local tuner and use what they recommend. Aside from that, Haltechs do have a large number of tuners willing to support them. The 750 may be enough depending on how much IO you plan to use, but on today’s tech I would consider the Haltech S2 or a Link Monsoon/Xtreme G4X. Those have faster processors and internal datalogging. Maxx ECUs have also become very popular and are highly capable.

These are stickers. The PO put them on so I don’t know where he got them. My friends have used these before, and I got magnetic ones for the Miata here too: https://www.autocrossdigits.com/

Yesterday was the PCA Autocross and got to take the Caterham there. It was a lot of fun to play with the car. Finished 5th of 42 in raw times and 1st in class. My only complaint is that it has too much understeer from likely a combination of alignment and tires. I raised the ride height a fair amount and didn’t check the alignment after, and I kind of expected I wouldn’t like the tires from my past experience in the Miata. But it’s ok, because I had a blast. unfortunately there is still something dripping down the fuel tank, likely fuel. I wasn’t smelling fuel however, so I didn’t worry about it and haven’t had a chance to check. I’m waiting for a bead roller to arrive to finalize the cap/breather job and will take better pictures of that setup then. Met another new Caterham owner that happens to be another SVT. He intends to roadtrip with it. Seeing his car on 13s made me really want a set and also verified that clearance is a problem with the wet sump. He offered to let me borrow the wheels to test fit sometime so I’ll have to take him up on that.

Yes, will do. I haven't had a chance to drive the car yet, but this weekends autocross will be a good stress test.

Thank you @wdb . That does make sense regarding the other line at the tank being for a fuel return. The SVT doesn't have a return line or a pressure regulator*. Instead the pressure is controller by the ECU as a return-less system. *: The regulator on these systems tends to be inside the tank, but I haven't been in there or found information on it. Apparently it may not have one. I went ahead and looped the line as in John's picture. Hard to take a good picture, but the breather goes around and behind the tank up to the rollover valve, then over the filler and back down next to the tank. and capped the other line, but this doesn't feel like a permanent solution. It's a vacuum cap and I feel that's going to crack and leak. Open to suggestions as to what to use on this for a permanent fix. As a note it was definitely this other port above that was sending liquid fuel. When I removed the line it still had fuel in it, and tilting the line at the front of the car dropped more fuel out.

Thank you John! This is perfect. Then I'll go ahead and copy this system and cap the other port on the tank unless told otherwise.