Update.

Henk tested the ECU by plugging it into another car alongside the ignition barrel and BCU. His car ran fine.

My only slight nagging worry is that if the issue was intermittent, then it might be that the issue did not rear its head in his testing, but I dont think I'm going to entertain that thought.

Weighing up the options of further electrical testing or just replacing the inlet manifold. Can't find much on removal/replacement methods though.

Sigh : /

Is yours the old Punto motor..??

( glad you didnt just fork out for the ECU.. - But a shame you cannot borrow a good replacement)

minimayhem said:

The reason the fault is thought so sit with the ECU is due to impossible readings coming from the temp sensor.

When the sensor is plugged in it reads an almost constant 20c, causing a large reduction in fuel going through the cylinders. This is causing my lean running and misfiring at idle/low rpm.

When the sensor is unplugged it should default to a -37c reading, which sometimes it does, and when this happens the car runs very rich but of course runs without misfiring. But sometimes the ECU is reading a temp sensor value of 20-25c.

If the ECU is reading a value from a sensor thats not connected to the ECU then the fault lies within the ECU...it would explain why the car is running so lean if it thinks the external air temp is so hot (and thus less dense.

Click to expand...

Were any plug.in readings taken in the other car..?

Or just a 'seat of the pants' it drives fine..nothing amiss report ...??

No readings, but the problem is so severe in my car it would be very apparent if the same issue occured on another vehicle. It would be ideal if there was someone close by to me that could lend me their ECU/ignition barrel and BCU to test out, but these cars are so rare!

But if anyone is around the home counties in the UK and happy to help that would be amazing

minimayhem said:

No readings, but the problem is so severe in my car it would be very apparent if the same issue occured on another vehicle. It would be ideal if there was someone close by to me that could lend me their ECU/ignition barrel and BCU to test out, but these cars are so rare!

But if anyone is around the home counties in the UK and happy to help that would be amazing

Click to expand...

Can you get some base line readings from a known good car?
Such as air flow at idle?
Previously you posted 5.5g/sec at idle which appeared high to me.

I've asked out on the Facebook group to see whether there are any takers! Alas I don't know anyone with a B in this country!

I went out with the plan today to run a voltage through all sensors to see whether the ECU was reading the correct voltage.

However the car is running absolutely fine. Best its ever run in fact.

There is no way the car is fixed, so this indicates an eletrical issue. Probably a wire is damaged and shorting out.

Will keep an eye on this....

Annnddd the problem is back!

Drove absolutely perfectly over the weekend and this morning. I then decided to detail the engine bay....what a stupid idea! In 2 hours I was able to clean the abs unit and area up to the battery.

And now the problem is back again! It's not a consistent as before, probably misfiring for a few seconds every 20-30 seconds, but it's definitely there again.

Of course when cleaning I was moving things around, so I must have a broken wire somewhere.

There's a lesson there somewhere ;-). At least you know the car can run properly, so it's not a terminal failure of something expensive.....

There's not a huge amount of wiring in that area, apart from to and from big fuses....I'm busy tonight, but if there's anything you want me to check/measure over the next few evenings let me know.

Are you sure the brake servo vacuum hose isn't leaking?

Mike

Still glad you didnt waste time and money down the ECU route

minimayhem said:

I went out with the plan today to run a voltage through all sensors to see whether the ECU was reading the correct voltage.

However the car is running absolutely fine. Best its ever run in fact.

There is no way the car is fixed, so this indicates an eletrical issue. Probably a wire is damaged and shorting out.

Will keep an eye on this....

Click to expand...

Now you know your ecu is good are you sure you can safely do what you propose with no danger of damaging your good ecu?

Voko said:

There's a lesson there somewhere ;-). At least you know the car can run properly, so it's not a terminal failure of something expensive.....

There's not a huge amount of wiring in that area, apart from to and from big fuses....I'm busy tonight, but if there's anything you want me to check/measure over the next few evenings let me know.

Are you sure the brake servo vacuum hose isn't leaking?

Mike

Click to expand...

Thanks Mike, really appreciate the offer! It was nice to have a weekend (and morning) where the car ran like it should do, and compared to how it used to run when I first got it it does go to show that all the work I've done to it (not in terms of mods, just replacing parts that were showing age/needed replacing) has had a good impact. But thats almost like its teasing me!

I've checked the vacuum hose a few times, but can check again. How does the hose connect to the brake servo, is it just a push/pull connector?

Its far to much of a coincidence that when I did the detailing yesterday, which involved removing the wiring brackets and moving the wiring around to clean the bulkhead, that the problem has reappeared.

In terms of testing wiring, I can verify the ECU is reading the correct readings fairly easily without risk to the ECU by using an ohmmeter to output a constant voltage and seeing whether the ECU is reading the same voltage, but the first thing I'm going to do is check the condition of the wiring around that loom and up to the fuse box. Also going to check the fuse conditions.

But diving deeper into the electrics is not something I want to do so have booked in the car with an auto electrician for next Tuesday as a backup. I've got replacement loom wrap coming this week, so during the evenings/weekend until then I'm going to strip back the loom and check the condition of the wires, check the condition of the fuses and replace if they even look slightly damaged/suspicious.

Not sure, but I'm sure you've excluded already by blocking off the port to the inlet manifold...

Not sure how much disturbing you did, but I'd be tempted to unplug and clean up the connectors in the general area there's a few on the throttle body, and one that looks like it might go to the injectors?

I have, yeah, remove the hose, plugged the port on the TB and then replaced the clips around the area with new ones, in case they were dud.

Around the fuse box I undid the 2 x 10mm nuts holding the casing down, pulled it up and to clean under it. Also did the small c-clip that carries the loom into the interior and move the loom up to clean both it and under it.

Just checked fuses, all look fine. A quick visual check of the loom and wiring doesnt show any surface breaks so I'll need to pull back the casing for a proper inspection.

Also just hooked up to the ECU and the readings are the same as they were before sending the ECU off to henk. I wish I'd connected to it when it was running properly for comparitive readings!

If someone is available and willing, would you mind taking readings at idle and warm on the:

- 02 sensor voltage
- 02 sensor loop status
- MAF voltage
- Air intake amount

Just thinking (typing?) out loud now, but the first time the car started running badly was after fitting a brake line. That involved moving wires/knocking things around the ABS unit, fuse box etc.

The car ran fine over the weekend after sitting for 2 weeks, and now after moving the same area (and nothing else!) the car isn't running properly again. To me that sounds like far too much of a coincidence, especially given I drove the car around 200 miles over the weekend. The problem *must* sit in the ABS/fuse box/wiring area....

With the engine ticking over, and taking care not to touch anything moving or hot, gently wiggle each connection, and each wire, and see if it triggers a misfire. If moving a wire does it, gently move along the wire to find the bad connection.

When jiggling HT leads, use something insulated, like a good pair of insulated pliers, and do not touch the car with any part of you.