Electrical Issues

[Wallby 39]

Hi all,

 

I’ve got something strange going on with the electrics on my 205 track car where the stop and warning lights are very dim when I turn the ignition on.

 

A bit of history, I’ve had this mi16 converted 205 for around 18 months and the past 6 it has been off the road having some new exhaust valves and head gasket. I finally got it running again a few weeks ago, took it out for a test drive and broke down after 5 minutes. After getting recovered home and having a quick look in the bay, I noticed that there was a loose connection in a join on the coil earth wire. Run new positive and earth coil wires all the way back to the fuse board and omex ecu and it started fine again. Took it out again, broke down again (luckily I went uphill from my house and was able to coast back home!). A quick look again and found a loose connection to the fuel pump switch. Blamed this, fixed it, and decided to go through the rest of the loom behind the dash to have a look at what else had been bodged.

 

It was at this point I remembered that I hadn’t seen the low oil pressure warning or stop light come on with the ignition – probably not since its been back together. This car has a large oil pressure warning light in the middle of the dash, and on removal of the dash surround, can see that it has been connected to the feed for the stop light, so I would not have seen the stop light since I’ve owned the car. I joined the stop light wire back in (a red wire, can’t remember the no.) and had a dim stop/warning lights come up – disconnecting that wire again did not make any difference to the other lights.

 

I was playing around with connectors by the fuse box, disconnecting  then re-connecting, checking voltage and continuity when I noticed that the lights were now on much brighter. Started the car and it ran fine, seemed to start a lot easier too. Leave it a week, put the dash back together and put the alternator back on as I was getting that checked over, and the lights are really dim again!

 

I’m after a bit of advice on what to check and where to start really. I’m thinking of going through the connectors again and seeing if I can pin point when the change from dim to bright happens. So far I have disconnected the engine bay loom – no difference, and checked the voltage at the coil, 12V showing on the positive, and approx. 4V showing on the earth! That can’t be good! The coil earth runs straight from the coil to the ecu.

[Wallby 39]

Small update on this, the ecu and main earth's are not earthing properly when the ignition is on.

 

Also, wire 32a only has 4v and comes from the ignition barrel area, so think this needs looking at. 

[pug_ham 244 3 Cars]

Does the oil pressure gauge work as it should?

 

I think something as simple as mixing the stop light & oil pressure sender wires so they are on the wrong senders causes these symptoms.

 

It's a simple case of swapping them over but easily done with them hidden where they are.

 

g

[Wallby 39]

Managed to sort this last wekend. Turns out it was the fairly new adjustable oil pressure warning switch that was faulty!

 

Hopefully thats all the wiring issues sorted now so I can get on with driving the thing!

[Wallby 39]

Following on from this, I still have a really bad missfire! The car idles and revs fine when stationary, but under load there is a really bad missfire. 

 

I have been changing parts over the past few weeks, gone through new plugs, leads, dizzy cap, rotor arm and coil. Struggling to think of what else I can change. Compression check came back ok.

 

One thing that is worrying me, is that I can connect to the Omex fine when the ignition is on, but it disconnects and won't re-connect when the engine is running. 

 

I have it booked in to a good garage in a few weeks, any ideas as to what else I can check before I take it up there?

[jackherer 543]

16 minutes ago, Wallby said:

One thing that is worrying me, is that I can connect to the Omex fine when the ignition is on, but it disconnects and won't re-connect when the engine is running. 

I had something similar with my Emerald after changing spark plugs. I had inadvertently fitted non-resistor type plugs, you have to make sure they have a suppression resistor or they generate so much electrical noise the ECU constantly resets.

 

For most manufacturers it just comes down to having an R in the part number. I was surprised to find that genuine Pug spark plugs for a 405 Mi16 were non resistor type! The  Bosch Motronic ECU can somehow handle the noise but the Emerald can't.

 

I've also had a similar issue with a different 205 running an Emerald, it had a home made tacho converter module that seemed to generate noise and stop the laptop connecting while the engine was running.

[Wallby 39]

Yeah I read your thread on that and fitted some resistor type spark plugs last weekend! I think it helped, but the issue is still there.

 

Interesting that you've seen this issue with a tacho converter, I have one of these fitted. Do you think it will be enough to disable this in the software to test or would it be better to dis-connect it?

[jackherer 543]

You'll have to disconnect it to rule it out.

 

If that doesn't solve it you'll have to go looking for other sources of electrical noise.

[jackherer 543]

Other things to check/double check are grounds and battery terminals etc. I know you've already looked at them but it's worth re-checking.

 

Also the wiring to the crank sensor is worth looking at, ensure it is good quality shielded wire with the screen only grounded at one end.

[Wallby 39]

Thanks for that, few things for me to look at in the week.

 

Im also thinking of running a new earth and power supply to the ECU, as I think the ECU is spliced from the coil supply.

[Wallby 39]

Managed to try a few things on the weekend, new power supply and earth for the ecu, disconnected the tacho driver and checked the earths again. Still have a missfire.

On ‎3‎/‎3‎/‎2020 at 11:20 AM, jackherer said:

Other things to check/double check are grounds and battery terminals etc. I know you've already looked at them but it's worth re-checking.

 

Also the wiring to the crank sensor is worth looking at, ensure it is good quality shielded wire with the screen only grounded at one end.

I didn't have time to do a lot with the crank sensor. I had a look at the loom near to the ecu connector, and I can see that the crank sensor has a shielded cable, but i'm not sure if the screen is grounded. Will look into the cable at the sensor end this week at see if it is grounded there.

 

Just for clarification, this shielded cable, how is it usually grounded?

[jackherer 543]

1 hour ago, Wallby said:

Just for clarification, this shielded cable, how is it usually grounded?

I'm not familiar with the Omex ECU directly but I assume it is the same as others. This is the line from the Emerald manual:

 

Quote

Very sensitive sensors such as inductive pickups should be wired using shielded cable. The shielding MUST be earthed and at one end only (preferably at the ECU) to be effective.

 

So if the shield is connected to ground at the ECU plug make sure it isn't connected at the sensor plug end of the wire.

 

Does the laptop still disconnect when the engine is running?

[Wallby 39]

The crank sensor wire at the sensor end is covered in black tape so i'll remove that and have a look.

 

Yeah, laptop still disconnects while the engine is running.

 

I have spoken to Omex who have suggested putting an osciloscope on the coil negative, as it could be an issue with the ecu. If it is the ecu, Omex wouldn't support it due to the age, so new ecu time or try and find a 2nd hand unit.

[jackherer 543]

Can you tell exactly when it disconnects?

 

Is it the split second you start turning the engine over or when the engine fires or a few seconds after it fires? Or some other time?

 

[Wallby 39]

I think its when the engine fires. I say that because I could see the battery voltage change under cranking, and also it didn't disconnect when I turned it over but didn't start it up.

 

I was a bit worried that the ecu was losing power under cranking, but as the car does start I'd sort of ruled that out. It also gives a different error message than when I try to connect the ecu when its not powered on. It reads something along the lines of 'cannot connect to the ecu using COM port X'. So it is seeing something there, but won't connect.

[jackherer 543]

OK that's interesting. Have you checked the voltage once the alternator starts charging? With a multimeter obviously if the laptop is disconnecting.

 

Given the timing of the laptop disconnecting the alternator might be involved, either the regulator could have failed and the voltage is too high or there is a lot of electrical noise. Does the battery light work correctly? (I.e. goes on with the ignition and off when the engine fires)

[Tom Fenton 1,542]

Easier to test by just disconnecting the wiring to the alternator if it’s a suspect.

[Wallby 39]

I had the alternator off a few weeks ago and took it to a local company to get it checked over. They said it was working fine, but suppose it wouldn't take much to disconnect the wiring and try that.

 

Voltage is at around 14.5V with the car running, battery light comes on and goes off when the ignition fires.

 

I managed to have a quick look at the cps last night, below photo is of the sensor end. I take it that the red wire is the signal and black is ground? The black is not connected to the screen at this end, I'll have to have a look at the ecu end to see if they are joined.

 

[jackherer 543]

That looks right as long as the screen is grounded at the other end to the ECU.

 

Give it a rev while you're checking the voltage to make sure it still regulates to 14.5 at higher RPM too. Give it some load as well, e.g main beam and heated screen on.

 

Or as Tom says just disconnect the wiring and see if the laptop stays connected and the misfire is affected. I'd be inclined to take the belt off too, it shouldn't self excite without a load connected but if it's retained any magnetism it's not impossible. And if it does it could still leak a load of RF noise into the ECUs loom even if it's not directly connected.

[Wallby 39]

Screen is connected at the other end, so that all checks out. Hopefully get to test it with the alternator disconnected at the weekend.

 

Thanks for the suggestions guys!

[Wallby 39]

Well things haven't gone exactly to plan this morning, it now won't start at all! Made sure the crank sensor was re-connected properly, but I'm not seeing any engine speed under cranking, so thinking the sensor is the issue. 

 

Tried testing for resistance between the pins and its not even registering, so looks like the sensor is dead. 

[jackherer 543]

Yes you should definitely have some resistance on the CPS, 500-1000 ohms or something IIRC.

 

Hopefully it has gradually failed and you've found the original problem.

[Wallby 39]

Fingers crossed! New sensor coming Monday morning, still booked in with the garage for Monday afternoon. Nothing like cutting it fine 

[Wallby 39]

It works! Fitted the new sensor yesterday afternoon and the misfire has gone completely! If I had known that I could have picked up a crank sensor so easily and cheaply I probably would have changed it much earlier. Nevermind, its fixed now ready for some good weather (hopefully!).

 

I still think the laptop gets disconnected when the engine is on, but I noticed that under cranking the 'connected' light is flashing between green and red, so it looks like its getting disconnected under cranking aswell as when the engine is running.

[Tom Fenton 1,542]

Good result.