Working kinks out of a new build - engine idle and grinding noise from rear

[frizille]

Hi everyone, looking for some ideas to troubleshoot two post-build kinks. The car has about 30 miles on it so far and has developed two oddities. A video of them can be found at https://youtu.be/XS8f_hLe3QA.

 

1) The first issue is what sounds like metal-on-metal grinding noise from the rear of the car. It's there when driving, although hard to hear over the wind + engine noise. It's very pronounced at slow speed though and you can hear it very clearly at 1:44-1:47 as I come up to the stop light. It doesn't always do it though and alternating light vs heavy brake pressure doesn't seem to trigger it more or less. It's kind of random so far or at least I haven't figured out the condition to reproduce it yet. The brakes feel fine - we did some aggressive test stops from 40mph on a flat stretch of road (with nobody around us) and the car stopped great with no issues.

 

2) The second issue is a weird idle which I've been troubleshooting since the first time we started it. At first, the idle seemed very low and would stall out. I fixed that by adjusting the idle screw on the throttle body. I've got it set now for somewhere between 1500-2000 RPM but seems to want to continuously hunt back and forth pretty freely. You can hear the motor hunt back and forth when we're stopped between 1:48 and 3:25. It actually settles down to about 1500 RPM for a few seconds and sounds stable, then starts back hunting between 1500 and 2000 right after without the car moving.

 

Any ideas?

[glenntwincam]

I'm assuming since this a new build , you have a OBD2 port . plug in a scanner & see if there are any codes . could be IAC valve or TPS sensor or ??

[yellowss7]

Is it possible that your handbrake cables are rubbing on the axles?

[frizille]

I'm assuming since this a new build , you have a OBD2 port . plug in a scanner & see if there are any codes . could be IAC valve or TPS sensor or ??

 

Good idea; just tried it and my OBD bluetooth thing won't connect. Apparently I've got an Android only one and no longer have an Android phone. Amazon will have a replacement here in 2 days - will check it when it shows up Wed.

[frizille]

Is it possible that your handbrake cables are rubbing on the axles?

 

They look far enough apart when the suspension is under load that they wouldn't... but will definitely double check.

[frizille]

Apparently the MBE ECU doesn't speak OBD, but does have an OBD port to talk CAN over. I've got to order the right USB to OBD dongle from MBE to read codes apparently. In other news though, I did find the MAP sensor screw had backed out (stripped apparently) and wasn't even finger tight - there was a bit of a gap between the MAP sensor and the intake. A large zip tie over the intake and sensor fixed that and the engine seems to be idling better but still has an odd bobble to it. Will post back up once the cable arrives and I can read the codes.

 

Still investigating the rear end noise.

[Croc]

The grinding noise is rotational related from listening to the video and sounds like a brake pad is rubbing on a disk. My guess - Inconsistent calliper operation so that after it is used initially for braking and then released it does not retract fully and so is rubbing on the disk? Failing springs in the calliper?

 

I last had this when a front wheel bearing was failing and it produced a similar noise effect with no ill effects on braking feel.

 

I am not sure you will see codes even after getting the cable. Codes are an OBDII thing - CAN is the protocol medium over which OBDII data is transferred. The MBE ECU cable (from SBD?) which can hook up to Easimap on your computer will tell you what the engine is doing but not tell you what is wrong with it. So you get real time data which may help but it is not the diagnostic tool that OBDII is.

 

Also not all data is tracked on the MBE ECU unlike a regular car. Another way of seeing what is tracked is by hooking a AIM SOLO DL logger to it (via the J1962 plug) and recording it for playback or look at the logger real time. Here is a sample of the data set on my car from a test drive (map is GPS based data and G force is AIM sensor but the rest is ECU). I had more channels available to read from the ECU but they were reading zero.

 

Edited August 7, 2015 by Croc

[frizille]

Thanks, Mike, for the info - yes, it's a SBD cable. I spent some time reading on OBD this weekend and had arrived at the same conviction; not sure it will help. No idea why Caterham doesn't use just a standard OBD supported ECU(?) - it seems much more helpful than the MBE one. There's at least 1 US car that was a EU CSR175 Duratec build and has an Italian ECU which does support OBD, so I know there's a possibility out there to support them from Caterham. Anyway, not material to me figuring out my car so I digress.

 

As to the noise - the e-brake cable looks fine, no rubbing, and tried pushing, pulling, jumping around on the car to watch the suspension flex a bit and no rubbing that I can see. I took the car out for 30 minutes on Sunday when it was prime heat of the day (~95F) and it was silent for the first 5-10 minutes. However, after doing a few easy stops coming up to stop signs and stop lights, it began doing it. It seems heat related and/or usage related - more stops = more noise. I also noticed if someone pushes on the pedal you can hear a faint "PFFTTTT" from the caliper. There's no fluid leaking though and it's been bled three times; no air is coming out of the nipple.

 

The engine idle is slightly better, but mostly the same as prior. It seems putting a zip tie around the MAP sensor and making sure it was screwed in tight to the intake (it's slightly stripped out) didn't improve anything.

 

The car did start doing 2 new things though, which may or may not be related. The first thing is the brake warning light on the little LCD bar in the speedo flickered on after making a right turn. I've got a hunch that's the fluid just sloshing around in the brake reservoir. The level is between the min and max about half way - I assume topping that up will resolve it and will do that once I order some fluid. The second thing it started doing is the car gets VERY jerky at slow speeds in 1st or 2nd gear. While driving through a parking at ~10mph the car started jerking back and forth and immediately pushed in the clutch. Jerking ceased. Putting it back into 2nd gear rather than 1st and it was still jerky, just less so. That's the first time it's done that with ~50 miles on it. Driving at normal speed and acceleration/braking it feels fine, no jerking. It reminded me of learning to drive a manual transmission 20 years ago with my dad - it was that same jerking motion when you screw up getting the car moving in 1st.

 

Taking the odd engine idle, odd brake noise, new-found jerkiness, and fluid warning light all together what are the chances there's a problem with the brake / clutch lines? Everything has been bled so I know fluid is getting to the right bits, but it seems like the only commonality between them. Maybe more air is trapped in there or air is getting into the lines somehow?

 

Any ideas what to check next?

[coffee break]

My vote is for a vacuum leak for the engine problem. Possible around the MAP sensor. Squirt some carb cleaner on suspect places and listen/watch the RPMs.

As to the grinding noise, exhaust system?

[jlumba81]

Propane also works for finding vacuum leaks.

[frizille]

Thanks all for the suggestions. I've figured out the brake issue and happily report it's resolved. It turned out to be the bolts which hold the caliper to the DeDion ears. During the build I couldn't find the spacers needed between the caliper and the ears so left them loose, found the spacers later on, attached them... but must never went back to torque the bolts because they were not marked with my paint pen. While the car is on the ground or e-brake applied everything looked tight and normal, no extra play, so thought they were fine. But when I got the car in the air on jack stands, climbed underneath, and had my girlfriend spin the wheels I noticed a double clunk - first clunk from the play in the diff which was normal, but a second clunk of the caliper moving back and forth 3-4mm. Very quickly afterward found the culprit, torqued to 47NM, and this time marked with the paint pen.

 

However... the engine idle issue still remains. I've tinkered with the idle position screw on the throttle body without much success although the car now idles better in the 1300-1700 range. Occasionally it will calm down and idle perfect - just haven't figured out what makes it do so yet. Have not found any vacuum leaks either and been over everywhere I can think of. I'm thinking maybe electrical - my gas gauge and speedo are both on the fritz and work on and off.

[frizille]

Posting here in case it helps others - to fix the idle issue I ended up doing a TPS reset by turning the ignition from off (position 0) to position II, but not actually starting it,. Do that 10+ times (I did 30 just to be certain) repeatedly and it will reset itself. Idle was much more smooth immediately after doing the reset. Now I just need to re-adjust the idle back to the normal range now that the TPS is reading accurately and I'm not trying to counter balance its bad reading.

[frizille]

Speedo fix was a bad speedo sensor - by moving the wire a bit you could get the LED to short out. Replaced the sensor from Caterham and everything is functional again.