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Engine running fault following a damaged crank sensor
Engine Running Rough after a track day
 
Engine running fault following a damaged crank sensor
Question: Sorry to bother you but I am being driven to distraction with a running fault on a 9A4i system. It's a 1.3L Swift engine on new Weber 40 DCOE's. The car was running beautifully prior to breaking an engine mount and damaging the crank angle sensor. I fitted a new SBD unit, rechecked the air gap expecting all to be well. However, the car now has a horrendous running fault. As you snap the throttle open it bogs down until around 4000rpm, eventually picks up and feels ok until another definite (almost rev limit like cut) at 6800 rpm, picks up again after that until the limiter at 8000rpm

Any ideas or would it be worth sending you a log of the fault?

Answer: From a brief reading of your email, I think that it is one of three things;

1.  When the engine mounting broke, the damage to the crank sensor also damaged the connecting wiring and potentially maybe trigger wheel at the same time.

2.  There was always an underlying fault that was ready to have an issue and the breaking of the engine mount has simply brought the fault to light.

3.  There is a fault with the fuelling on the carburettors and this is creating the problem.

How to investigate whether the problem is fuel or ignition.  Initial checks can be done by simply looking at the rpm on Easimap 6 and taking the engine speed up to each area where the problem occurs, then look to see if the engine speed becomes erratic, i.e. different to that of what the engine is physically doing.   So, for example if the engine fault is at 4000rpm, and the engine speeds up and slows down again, the rpm trace should follow this.  If the rpm however, shown on Easimap 6 has a much greater change e.g. 4000, then 1500, then 3000 basically showing readings that the engine is not actually doing, this is likely to indicate that the ECU is getting corrupted information.  Then what should be done is to add 3 real time panels to Easimap 6 to help diagnose the problem, these are under the development section and you should use the Search function to find them; 1st - Bad missing tooth count, 2nd - Reset count and 3rd (only in later software versions) - Tooth count. 

The first panel will give you a random number when keyed on for the first time, for example it could be 202, when you begin to crank the engine, the number is likely to rise by 1 or 2, once the engine is running, this number should not change.  Basically what happens is each time the engine revolves, the ECU is looking for a tooth count that matches its trigger wheel pattern, so for example if the engine has 60-2, it looks for 58 teeth then a gap of 2 teeth.  If it does not see this for whatever reason, the ECU will start again and add 1 to the Bad missing tooth count number.  As I said this number shouldn't rise once the engine has started and if in the area where the misfire is occurring, the Bad missing tooth count increases, it indicates that the ECU is getting false information at which point you need to investigate the trigger wheel, crank sensor and wiring from the sensor to the ECU checking for damaged wiring or potential proximity to high energy outputs such as coils and alternator.  If the number does not rise, this indicates that the ECU is reading correctly the engine speed and there are no issues with the crank speed signal information.  Test at all points in the rpm range where the issues have been reported just in case you have more than one problem.

The second panel again is a random number, which will increase by 1 each time the ignition is switched on, also if there is faulty wiring to the power supply and potentially when vibration occurs, if contact is broken to the ECU, the reset count will again rise by 1 each time the ECU is reset.  It should be noted that the Bad missing tooth count panel will also rise by 1 at the same time, so care should be taken to look at both panels together, for example if only the Bad missing tooth count number rises, this indicates faulty crank signal information, but if the reset count and the Bad missing tooth count rise at the same time, it is likely that only the power supply to the ECU itself is being broken causing the Bad missing tooth count to rise as the ECU reboots each time. 

The third panel, the Tooth count counts each individual tooth and is normally only required on an engine that will not start so you can confirm that the ECU can actually see any crank tooth information.

Finally please ensure that you always run the latest Easimap 6 from the website, as new functions are always added and one panel which is very useful, which is on the basic page is the ECU status.  It describes potential faults as the ECU sees them as well as giving the current ECU status and if the ECU is getting poor crank signal information, a warning in this panel will be given.

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Engine Running Rough
Question: I went to a track day, the car was running a bit rough, but naively I put that down to the mapping being a bit out. I could not fix the noise issue so ended up bringing the car home - it was good to get the car running though, shame I could not run longer as the track was just starting to dry out.

Anyway - on inspection yesterday, the rough running was down to the injector wires for cylinders 3 and 4 being on the wrong injectors - not sure how this happened but the upshot is that, having run the car for a few laps like this, I think I may have knackered the pistons on these 2 cylinders - I will confirm for sure this coming weekend. Symptoms are very poor idle, removing ignition to these 2 cylinders does not make the idle any worse, swapping coils and plugs with cylinders 1 and 2 makes no difference (removing coils from 1 and 2 stalls the car), wet plugs, and colder exhaust manifold on cylinders 3 & 4, difficulty revving, would also explain why everyone was faster than me!

I know that if I am taking the engine apart to put in new pistons in I should probably upgrade everything, but at this stage I am keen to get the car running without spending a load more cash.

Replied on the phone: We received this email from one of our customers, you can see that he was obviously worried that he had a major problem. Since I hadn't see the vehicle that long ago, I knew that it was unlikely to be anything serious but it is quite often that a very small problem can lead the owner to think the worse.

I spoke to the customer on the phone and said from what he had described in the email, it sounded like a simple question that the butterflies had potentially closed down or gone out of sync, this lets in less air at tickover and means that the engine runs richer on the cylinder or cylinders where this has happened. This causes the spark plug to soot up and even if the spark plug is removed and cleaned when tested outside the cylinder e.g. laying on top of the engine will get a good spark. Unfortunately when the spark plug is placed back into the cylinder again, the pressure created within the cylinder increases the resistance and the spark inside of jumping the gap tracks down the side of the plug. The process that the spark plug has gone through when it has been playing up quite often prevents the spark plug from recovering. If the spark plugs are replaced with a brand new set, check that all butterflies are synchronised and that the correct kgs of air per hour is going into each cylinder correctly and that the TPS sensor voltage is correctly set up. This will normally rectify most problems.

His worry that the injectors plugged in incorrectly could have caused some damage, this would not be the case as the fuel being supplied was the same to all cylinders.

Obviously you can see from his final email, his problems are now solved and everything is running perfectly. This is a mistake that is regularly made by customers with engines that are perfectly programmed and then take them to a rolling road and end up spending large sums of money having the engines reprogrammed to rectify a fault which had nothing to do with the programming. Simply a small issue with the throttle butterflies going out of sync causing a rich mixture which gives very sooty plugs, when all that was required was accurate resetting of the butterflies.

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