So here we have a technical fault that was dealt with in the workshop recently, thought it may be interesting to see what you guys would make of it and see if maybe we have a budding technician or a right good guesser among the membership!! I can tell you this is a weird fault with a surprising conclusion, read it all through before making any conclusions.
So let start with some background first, a standard non turbo running well with no major issues that developed a small water leak, the owner with some tech help from Jamie here and some pipes removed the plenum and replaced the offending pipes, the work seem to go well but once all back together the first start up was less successful.
The owner went over his work and with the exception of switching the coil pack connections on number 4 and 6 cylinder could find nothing to cause the non starting.
However with a fresh battery charge and some long starter motor action eventually it started, this is where we gave some further advice on checking vacuum pipe connections, electrical connections etc. at this point it was realised the det sensor and near side variable valve timing solenoid connectors were the wrong way around and so with these correctly plugged in the owner happy to do a road test.
This is where it all went wrong! the performance was terrible with a huge performance loss, lethargic acceleration coupled with a low tickover, and a sheer reluctance to rev when stationary and in neutral.
The next stop for the owner was a very slow drive to the workshop for us to take a look.
So as mentioned this was very poorly running zed, as we knew the plenum had been off and the potential for air leaks after we went straight for a leak check. In all fairness there was a couple of small leaks and one major one where an air pipe had been left disconnected under the plenum on the n/side.
Further checks of the smaller vacuum pipes found the egr valve incorrectly connected and so this was sorted and confidently the engine was started, but argh!!! exactly the same! no improvement at all, static revving the engine just produced this weird really slow build in engine revs whether the throttle was opened slowly or wide open, a seriously muffled sound from the exhaust.
So to recap, the engine has serious performance issues, but will not rev, now we know there is no air leaks, no pipe work errors, no misfires on odd smelly exhaust was no surprise because clearly something's no right but either way time for the ConZult.
ConZult screen One
So here is the first screen shot, for the uninitiated the there is a fair bit of info on it that is important and some not to worry about but in short there is a faulty O2 sensor a good timing reading ( confirmed with a timing gun) a high iavc ( idle control ) valve reading but the temp is only 67C so again not to worry about yet, BUT take a look at the injection pulse 4.03 ms !!! this is practically double what it should be, but with a an A/F reading of 108 % it could be easy to miss it as excessive enrichment. High injection pulse can be cause by air leaks due to the readings at the air flow meter been corrupted by the leaks or and very common a failed afm can give poor or corrupted readings that are still in its total range so hence no fault code error readings.
ConZult screen Two
So trying to keep it brief the next screen shot is some time on, lots of things have been checked again and again including timing, air leaks , vacuum pipes, throttle balance tps o2 sensors disconnected and reconnected, spark plugs checked cambelt timing checked all with no improvement.
So this particular screen shot shows an amazingly odd set of readings if you look at the part throttle tps reading against the actual engine revs of 3,700, this again was a hard, slow and lethargic engine that was slow to pick up. The injection pulse of 12.5ms is worrying so was the awful smell coming from the exhaust serious incomplete combustion, luckily we have a very well ventilated workshop!!
A split second after this screen shot without any more throttle opening the engine revs to over 6k very suddenly, releasing the throttle the revs dropped to idle, each time we tried the it the same thing happened. Now this is all very odd but even more so when you consider that we had the air flow meter disconnected at this stage!!!! yes that's right an engine revving at 3,700 and upwards with the air flow meter disconnected.
AFM Disconnected
So now we have moved up a gear with an engine that does not respond to the expected fault finding procedures as with the afm disconnected the engine should not rev pass 2,500rpm, oh and no fault code appeared in the ecu memory.
Ok guys so what do you think? just a little bit of fun, I doubt anyone would guess the exact cause of the fault because it was a bit bizzare in a simple way but had big repercussions.
So to recap.
Poor engine performance
Very slow resonding revs
Odd smell to exhaust
Swapped checked
AFM
ECU
TPS
Timing checked
Cambelt checked
Leak check
Abilty to rev to 6k with out an air flow meter
Jeff TT
The term "Disk warp" is often wrongly used as in most cases the effects ie.shaking steering brake pulsing etc is due to pad imprint. This is where pad material adheres to the disc face in uneven levels causing highs and lows that can be felt on the brake pedal. Mostly this is caused by excessive pad material temp been forced beyond its max working temp, this itself can be caused by poor quality pads, wrong applications or seized calipers. Good caliper and brake system maintenance is the key, ensure calipers are free and the use of branded pads as well avoiding sitting at junctions or in traffic for long time with your foot on the brake pedal. Jeff TT