chrispayze

I'm having a 'mare with the last throws of my supercharger installation, namely the electrics/electronics. A couple of weeks ago, I had the car idling sweetly and just had to add two sensors to complete the build, oil pressure and temperature.

I dismantled the wiring looms to neatly run some new cables for the sensors and all was well. I started pinning and connecting up the two oil sensors and before the end realised that the battery terminals clamp had slowly worked its way back to touching the terminal. Unsurprisingly, the cutting and crimping (and, in all probability, shorting) that had been happening seems to have fried the sensor circuit in the EMS, which has now gone back to AEM for repair.

I've got a 2nd EMS to try and get it working in the meantime, but its provenance is shaky, ie it might not be fully functional, which doesn't help with fault finding. I have unplugged the two sensors (at the EMS and at the sensor ends), just in case there's a fault in the wiring. But there seems to be odd readings from the TPS, MAP sensor etc and it run as rough as a dog, not smooth and very rich, I think.

There seems to be reading from the fuel injection pulse (in milliseconds) whilst the engine isn't running too, which seems strange. Is that normal? The TPS voltage normally goes from. 0.2ish to 4.7ish, but doesn't go below about 0.4V now. O2 sensor seems roughly where it should be, although obviously it's difficult to tell exactly. MAP reads 1.9PSIg with engine stopped and seems to go negative when running, which is odd with a SC!

I've done some voltage testing at the TPS and MAP sensors, both on the disconnected connectors and by probing whilst connected there seems to be 4.5-5V on the signal lines, earth lines seem to be at about 0.4V (when disconnected from the sensor) - edit: apparently the signal lines go high when disconnected, normal behaviour.

My current conclusion is that this 2nd EMS has a faulty sensor circuit, but I want to double check everything is right first, particularly as I'm now starting to question myself and my wiring, even though it's exactly how it was when it was running. I'm even starting to get a bit fed up with the damn thing.

If anyone has any ideas on what else to check, before I declare the 2nd EMS faulty? I'd also like to reduce the risk (and my paranoia) that something buggers up the repaired EMS when I get it back. Basically, any help or motivational speeches greatly appreciated!

Rgds
Chris

chrispayze

Wiring is as per the attached diagram.

[attachment=88457::]



Attachment 88457

s2konroids

The circuit on board that has a surface mounted resistor has likely blown, it shares same circuit as tps map and coolant I think. It's purely for grounding.

chrispayze

Well, I'm (re)gaining confidence in my wiring. Checked continuity of every single connection I've made (ECU plug to sensor plug) and between every connection I've made (to ensure no shorting) and even checked the pin outs again. All is well. Checked resistance of the TPS and it seems to change as I move it, from near zero upwards. Difficult to check the MAP sensor unless I had a separate 5v source, which I don't. Anything else I can check that anyone can think of?

'roids, thanks for your insight into the inner workings of the EMS! I went through everything, even reflashing the firmware and loading the original map that Romain gave me. Funnily enough, the coolant temperature started doing funny things as I started it up. The OEM gauge went up a bit and and back down again almost as soon as the engine was started. I noticed some slightly strange intermittent behaviour such as the interior light getting brighter as I put the key in-out (and the beeper started/stopped), plus sometimes with a power recycle (ignition on/off) the fuel pump didn't cut in and AEM Tuner didn't pick up the EMS being connected again.

Do those symptoms confirm your hypothesis?

chrispayze

'roids, is it possible to open up the EMS to check the resistor? Do they usually fail visibly?

s2konroids

Nope not visible contact aem you can remove them quite tricky though they are tiny and don't burn the board, you check resistance it's a small amount.

markforrester99

Have you recalibrated the throttle when you have been setting everything up? Typically the throttle measurements will bounce around abit at idle. Loads of reasons for that ie heat effecting resistance etc but it shouldnt move loads. You need to recalibrate the throttle if youve been mucking about with it otherwise the ecu wont know when to attempt to idle.

My AEM recently has had the issue of not repriming the pump after a stall. Its almost like the AEM crashes for a few seconds. If i turn the key back to the fully off position for a short while you can hear the pump prime again when turn it to the ignition position. I have only noticed this recently when i fitted the new injectors and getting it to not stall when the AC came on was proving a pain. Its all sorted now thou.

Also just for your own sanity. Youve pulled alot of wires about so i would get a jump lead and connect it from the negative terminal of your battery and then to a good position on the inlet manifold/block just so you can rule out it being a poor earth being the cause of the issue. The only reason i say that is because a dimming interior light would make me think maybe you have a dodgy earth.

Hope you get it sorted soon. If its any consolation i spent 3 hours last night trying to change my passenger engine mount and finding out that as i undone the bolts that secure it to the block that one of them stripped a fair bit of aluminium out of block. After alot of swearing and some emergency work with a metric tap i got it to all go back together again. Nothings ever easy eh!

chrispayze

Thanks, some more things to think about. I have been recalibrating the throttle each time, but I haven't had it running long enough for heat to affect it. The voltages are odd, even when stone cold.

Earthing hasn't changed from before, when it was running fine, but I'll try earthing the manifold anyway, just to be sure.

chrispayze

Tried that this evening, lots of decent continuity everywhere for the earth, and no difference. I think the original problem with the light (never seen it since) was something odd. God knows what. Still got rough running.

chrispayze

I did some more testing - Looking at the calibration table for the SoS MAP sensor, the 2V it was reading with the engine off is too high for ambient pressure, so I swapped it for the known-good OEM MAP sensor and found the following:

• Blowing/sucking on both MAP sensors induced a voltage change in the correct direction (positive blowing, negative sucking) - sensor seems to be working ok
• OEM MAP sensor was also reading high (3V, over 1.5psi) - suggests the MAP sensor is not at fault
• The ground pin voltage changed a little when I changed the MAP sensor (relative to battery negative terminal) - sensor ground circuit problem?
• The TPS voltage (at fully closed throttle) changed a little when I changed the MAP sensor - sensor ground circuit problem?

Seems to confirm that it's the sensor ground circuit in the EMS, mainly due to the ground voltage fluctuating relative to the battery negative, and the fact the swap of MAP sensors is affecting the TPS values.

I also noticed was the coolant gauge moved around (zero to 3 or 4 blobs and back again) without running the engine! Very odd...

Anyone any other thoughts?