hairball29 Posted December 4, 2017 Author Share Posted December 4, 2017 Yes, the gauge reads fine. It shows various AF readings as i change throttle positions. The car never dies once it's running, whether with the gauge, the o2 or both are plugged in, but they have to be connected after the engine is running or we get a no-start. Link to comment Share on other sites More sharing options...
hairball29 Posted December 4, 2017 Author Share Posted December 4, 2017 The O2 is the device that came with the gauge. It is a 6 core cable between the gauge and the O2 and that carries, live, earth so i cannot easily separate the gauge earth from the O2 earth. The 6 cores come together in a small plug which attaches to the gauge. I had suspected the PATs and moved the gauge, but that was before I noticed the unplugged O2 improves things. The excess O2-to-gauge cabling is under the dash so if that's what's making EMI, then it might be a factor. I'll go move it later and get it as far from the PATS halo as i can to see if that changes anything and report back. The gauge and ECU are about half the cockpit apart. The gauge is behind the gear stick, and the ECU is at the bottom of the passenger footwell Disconnecting the gauge will allow me to start. Currently i just pull the connectors apart, then reconnect, but i need a switch would be a more good version of that crudeness. I did try attaching the gauge to switched live, but of course switched live is on before the engine starts so it had no positive effect other than meaning the gauge goes off when i turn the ignition off. thanks for your input, everyone Link to comment Share on other sites More sharing options...
JohnCh Posted December 4, 2017 Share Posted December 4, 2017 Have you contacted AEM yet to discuss? They may have some unpublished workarounds you can try. -John Link to comment Share on other sites More sharing options...
hairball29 Posted December 4, 2017 Author Share Posted December 4, 2017 I haven't contacted them, but that is a good idea. Mainly I didn't because this used to happen with my USB in the cigarette lighter, too. This was before i had the gauge so i thought it was something more broad. I'm going to play with it some more and see if it is EMI from the wiring and device. I'll update you soon! Link to comment Share on other sites More sharing options...
hairball29 Posted December 5, 2017 Author Share Posted December 5, 2017 The plot thickens, folks. I have an SCT X4 for tuning. As you probably know, they plug in to the OBD port and nowhere else. They don't have separate power. I use the X4 in conjunction with the AF gauge to report the AF ratio for logging. Turbo Tom is tuning the car for me. Anyway. I had suspected my no-start was also happening with the X4 attached, and i just confirmed it by reading the voltage on the output side of the Fuel Pump Driver Module. When trouble comes, the voltage reads 0V on firing and the engine does not run. It reads 8V (ish) normally at idle. I don't think this is the only ECU symptom as it's not consistent, but it's the only easy way i have to measure if that ECU is acting up and a 0V definitely. My findings are: - X4 connected to OBD and AF disconnected and O2 disconnected from AF - no start - gauge attached but no O2 - start - gauge attached with O2 - no start - gauge and O2 connected but with wires completely pulled away from the dash and the PATS sensor - no start Apart from current draw, the only differences I am aware of are that the gauge alone uses an earth to the chassis. If the O2 is earthing through the exhaust, then it might be going through the motor and back to the battery. Today I have been under the car to clean up and ensure a good connection for the engine to frame earth. The battery to engine earth is new. I also made a new earth strap and connected to the body, but nope. Symptoms remain as above. I even ran a jump lead from the battery negative to the exhaust to give the O2 a different earth. Same I can get around all the above my unplugging/turning off everything before starting, but it's really doing my head in and i'd love to know why it's happening. Perhaps something's messing with the ECU's earth, but why don't the headlights or radiator fan cause trouble. Link to comment Share on other sites More sharing options...
papak Posted December 5, 2017 Share Posted December 5, 2017 Not sure if it would help but on the advice of Tom Carlin, I decided to attend to the ground system with great care. I have a ground strip behind the dash that is connected directly to the battery ground. Everything behind the dash grounds there. I also have one at the rear of the car for the fuel pumps, lights etc. That is also wired directly to the battery. I also have a #4 cable running from the battery ground to the aft bolt on the exhaust manifold. I might have other stuff happen but I DO NOT have any ground issues. I am on my third O2 sensor (???) but other than that, I have had no problems. I used 14g wire for the connections between the ground strips to the battery with all connections crimped, soldered and heat shrinked. Once the individual grounds are screwed to the ground strips, hit the screws with green Loktight. You can then measure the continuity with an ohmmeter from each device to the battery, switch off and switch on. if there is any resistance, at least you will know where to start. You can't rust any grounds to the chassis due to the varying density of welds, brazes and riveted structures. I have restored several old race cars over the years and this strategy has always worked. Link to comment Share on other sites More sharing options...
JPS Europa Posted December 5, 2017 Share Posted December 5, 2017 Ummmm...why are you on your third O2 sensor? OK. Two things. One thing- you need to eliminate voltage as the issue. Somehow, you will need to run a pigtail out of the ECU power line and get a meter on it. If the voltage sags below 10V, I would chase that. Second thing- How does your ECU sense crank timing? Do you have access to an oscilloscope? Link to comment Share on other sites More sharing options...
hairball29 Posted December 7, 2017 Author Share Posted December 7, 2017 Hi, I inserted a pin in to the back of the permanent +12v cable on the ECU connector and measure the voltage at cranking both with the AF connected, AND without. In both cases it dipped to about 8.8V. Without the AF on, it started ok. When i tested the battery during cranking, it dipped to about 10.5 V. Not sure where my 2V are getting lost. I'd like to look up where my ECU permanent live comes from, but no wiring diagram. The next step is to start trying to trace it so if i get anywhere, i'll update you. Link to comment Share on other sites More sharing options...
hairball29 Posted December 12, 2017 Author Share Posted December 12, 2017 Looks like the 12v is coming a fused connection directly from the battery. The cable goes into the loom, but the permanent 12v on the ECU definitely ends up at this cable according to my continuity test. Next test is to backprobe the earth(s) on the ECU and see if i can see a voltage drop or some other poor connection. Link to comment Share on other sites More sharing options...
JPS Europa Posted December 12, 2017 Share Posted December 12, 2017 As long as you have the wires hooked up, measure the resistance in that line. Link to comment Share on other sites More sharing options...
hairball29 Posted December 12, 2017 Author Share Posted December 12, 2017 As long as you have the wires hooked up, measure the resistance in that line. Do you mean the 12v? if so, that resistance was basically nothing. As far as I could tell, it's sound. Link to comment Share on other sites More sharing options...
xcarguy Posted December 12, 2017 Share Posted December 12, 2017 (edited) Another thing to try -- and someone please correct me if this is a bad idea -- is to jump start the car. OK as long as the battery in the car being jump started isn’t a lithium ion. Edited December 13, 2017 by xcarguy Link to comment Share on other sites More sharing options...
hairball29 Posted December 18, 2017 Author Share Posted December 18, 2017 I back probed the ECU cables. I used the ford green book wiring diagram to figure which was which. Tested them and learned that they go to their own cables that are attached to the battery. + and - have their own. If the - is disconnected, it doesn't affect the start, so it must be getting it's - connection some other way. The manual says there's more than one - I cranked it with the probes on a volt meter, and it dipped as low as 7.5v whether or not it started. As usual the no-start was caused by the AF gauge being powered up. Still don't know what's pulling it the ECU voltage down so low, but I've about reached my level of competence and am wondering if anyone can recommend a place in Atlanta that would take a look at it? Most mechanics panic if i mention kit car, so I'm looking for someone who might want to have a go. Thanks Link to comment Share on other sites More sharing options...
hairball29 Posted December 19, 2017 Author Share Posted December 19, 2017 I changed the starter motor since that's been a recommendation elsewhere from another Caterham person saying a bad starter pulled so much juice that it reset the ECU on cranking. I wasnt very hopeful, and it made no difference. The problem appears to be getting worse. It's often failing to start with nothing connected now. So, if anyone knows a place in Atlanta i can bring it, I'm happy to hear your recommendations? thanks Link to comment Share on other sites More sharing options...
1turbofocus Posted December 25, 2017 Share Posted December 25, 2017 Wish I was closer Tom Link to comment Share on other sites More sharing options...
hairball29 Posted January 11, 2018 Author Share Posted January 11, 2018 Well, I'm moving to Asheville in a few months, so I'll be a bit closer to you. If it's not fixed by then, I'll come by. Link to comment Share on other sites More sharing options...
Kitcat Posted January 12, 2018 Share Posted January 12, 2018 Lots of great se7ens roads near Ashville! Link to comment Share on other sites More sharing options...
hairball29 Posted January 18, 2018 Author Share Posted January 18, 2018 Lots of great se7ens roads near Ashville! Looking forward to it! Link to comment Share on other sites More sharing options...
hairball29 Posted March 9, 2018 Author Share Posted March 9, 2018 Hi, all I think it's finally fixed, so I want to record the outcome for now and for any future sufferers of this vexing issue! The car went to Motor Cars of Georgia, the Lotus, McLaren and other expensive cars dealer in north Atlanta. Their mechanic diagnosed the issue as related to the PATS (passive anti-theft system). Since he's used to Lotus and even McLaren earthing issues (even new McLarens have these) he found that during the non-start at least one of the switched earth pins on the ECU was not switching to earth meaning the coil wasn't functional. This was intermittent so it took a while, but long story short, something about the aluminium chassis being used as earth was interfering with the PATS 'halo' (sensor) and triggering the system. His solution was pretty easy, he moved the sensor as far from the under-dashboard wiring as he could, shielded its cable with aluminium tape, and fixed the sensor to a clean area on the bulkhead. It has not 100% fixed the issue when the AF gauge is on, in that half the time it won't start, but it has 100% fixed it when the gauge is off. Previously, the car was often hard to start when the gauge was off so I'll call this a win. Turbotom helped out so additional thanks to him. So the moral of the story, is keep your PATS sensor away from wires if you're using Focus hardware! Link to comment Share on other sites More sharing options...
Dave W Posted March 10, 2018 Share Posted March 10, 2018 When designing the first Z06 aluminum frame it was found that the electrical grounds attached at the riv-nuts connections would build up an oxide between the aluminum and the riv-nut case. The solution was new drive screws and an 18mm thick aluminum button welded to the chassis for all the electrical grounds. If you have an aluminum chassis, extra care is needed when making grounding attachments because of the oxide layer on the aluminum. Dave W Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now