I am also chasing my tail to try and resolve a miss in my engine. Essentially the engine runs ok but is definitely down on torque and has a small miss. It is also chugging through fuel compared to normal and you can hear it over-running far more than it should. Whats making this stranger is it doesn't happen all the time. Occasionally it clears up and the engine feels fantastic again.
I am running it on 98 octane with the fuel plug removed as I always do.
I have checked for air leaks as best as possible. Replaced spark plugs (they were due anyway). Cleaned all the intake side of the engine (removed plenum and disassembled) including the idle air bypass. I have a fuel pressure gauge attached and the pressure appears good. Have done a few tests and all returned correct responses. Fuel pressure drops overnight from about 2.5/3 bar to about 0.5 bar - is this more than normal? However it starts fine from 0.5 bar.
Have interrogated the ECU and have no error codes stored. TPS appears to be set correctly. I have swapped a good AFM with no change.
What next? Could it be an earth for the engine beginning to fail?
Hi,
A couple of things,
As being twinspark having 2 sets of ignition components it's pretty hard for the engine to develop an electrical miss.
If it is an ignition related miss, it is likely that your engine is only running on one coil ( if it were running on both coils you wouldn't feel anything because the other system would disguise it). By unplugging one ignition module, run the motor and see what it's like, then plug it back in and unplug the other module and see what happens. If it runs both in both scenarios , the miss is likely to be non ignition related.. ie compression, valve ,fuel related or and intake runner issue. If it won't run when you try to run on one coil- Check back to your secondary relay that runs the 2nd coil and the start checking out the coil, module, fussy etc.
It could be a crank angle sensor - my track car did some weird shit once - missing, not revving and cutting out. Turned out to be a faulty crank angle sensor.
Because you're using a lot of fuel, having running issues and running on, I would be checking the fuel system.
Check fuel pressure at the rail- your fuel pressure regulator could be sticking and over pressurising the rail and flooding your injectors. Whilst checking your running fuel pressure take off the vacuum line to the reg, if the pressure climbs too high out of spec it's ok. If your pressure is too high and doesn't change when doing this i would be swapping the regulator. Of course, check you have vacuum at the regulator.
Have the injectors flow tested-maybe one is dribbling and putting too much fuel into one cylinder and snuffing out.
Check the Injector pulse with a noid light to make sure you have a good pulse on all injectors, if one injector has a pulse width that is too long that could cause problems- that would be ECU but I think this is highly unlikely.
That should enough to start with, keep us posted.
Luke
Hi GTVeloce
Had a similar problem with my JTS and due to the momentary misfire with the EMS light coming on then off, the fault code did not register. Refer to link below on how to diagnose the problem with diagnostic tool using I/M readiness mode.
http://www.alfaclubvic.org.au/forum/index.php?topic=2380.msg108161#msg108161
cheers
bonno
Hang on! WHICH type of Twin Spark are we talking about here? The type used in the Alfa 75 or a modern post 1999 Twin Spark?
We are in 160 series, so I assumed it was the 8v.
Bonno is talking 16v.
That's what I thought, just didn't want out original poster to get confused.
Sorry guys my mistake, thought it was the 932 series twin spark 16 valve.
Old 8V TS engine. Got it working finally this weekend.
Found a number of problems actually that all combined. So, I was fairly sure it was fuel related and checked or swapped almost everything on the fuel system side of things. I even got the injectors professionally cleaned. Interestingly they were in pretty decent shape considering how old they are. Finally she got so bad I basically couldn't drive it at all.
I'm fairly sure I had given the ignition a brief check early on but I have also found the ignition system fairly bullet proof in the past given the redundancy of two ignition systems and this was an over fueling issue so it is fuel related, no?
I Discovered that it wouldn't start on one coil and would start, but run poorly on the other. Closer inspection showed a rotor button on the cam dizzy that was basically burnt to a crisp! The centre electrode on both the rotor and the cap had fried itself and yet this was the dizzy that still worked. The crank dizzy looked ok. Hm. Decided to give her a birthday and bought both new rotors and caps. Better, but still wasn't smooth and and with a surging acceleration and plenty of over-run regardless of whether I ran it on one dizzy or both.
At this time I also discovered one of the cables going into the coil module had pulled out of its socket. This was an earth cable that doubles back and also provides an earth to the second coil. Interestingly the coils have two separate earth cables each. Didn't make any appreciable difference.
Decided to replace HT leads as well. New ones arrived and I measured the resistance difference between old and new. While they change depending on length, there was a clear difference between old and new. Old leads had around 4-5K ohms while the new ones were all (except the longest one) under 1K ohm. While replacing leads I checked and discovered that the leads on the crank dizzy were 90o out of phase. So the second dizzy was sorting working as a wasted spark which is not really the idea of it! Reorientated the leads and voila! She runs sweetly again.
So, in short, the leads were old and poor, the earth wire had pulled out, one of the dizzy's was burnt to a crisp and the other incorrectly configured.
I was so relieved to have it work properly again I decided to have another go at fixing the clock (seriously, probably the 20th time). This time I rebuilt it and she worked! Am going to buy a lotto ticket tomorrow.
Well done. Always great satisfaction when you get something sorted in the end :)
My joy was a little premature :'(
The quick blast around the block seemed very positive at the time. However, cold started this morning and she started beautifully and was about to settle into a nice idle but instead she stalled. Hm, not a good start. Tried again and this time she idled but not well. Smoothed out a little once she was warmed a little but still popping and missing slightly, both at idle and over-run (i.e. changing gears gets three or four pops from the exhaust). So she is still running rich. If I open the taps she runs really well but idle, low speed take off and partial throttle are clearly not quite right. Still, this is much better than it was so the work has not been entirely in vain.
Ok, what could cause a rich mixture, starting in order of likeliness?
1) air leaks - triple checked everything and can't see anything except the oil dipstick is a little loose
2) poor spark - just replaced or checked everything in the timing system and all seems in order...now!
3) AFM out of spec - swapped with a spare recently
4) TPS out of spec - fairly recently changed
Known problems: still to be rectified are
1) I have a small exhaust leak somewhere near where the manifold meets the downpipes and before the 02 sensor however, I am running the engine on open loop at the moment so that shouldn't have an effect, true?
2) oil dipstick is loose but you still get a change in idle when you pull it out which should signify it is sealing well enough
3) slight oil leak from cam cover
Any ideas where I should start next? I have a second TS engine which works well so have parts to swap (which I have been doing) but also need that car to drive so trying not to cannibalise too much.
Interested to see how you go with this - my Alfetta GTV is currently showing some very similar symptoms (twin carbs not EFI though obviously).
How does your TS start after you've been on a longish drive and then had it turned off for a while? Mine can be a bit difficult to get going again - kinda feels like its flooded.
Also have the problem of a bit of over-run when I come off the throttle, and hesitation if I suddenly floor it, like it's briefly either starved or flooded.
I know you might have checked it but perhaps have another look at the connector plug to your AFM. It is difficult to plug in as it is located under the AFM but sometimes you might have bent the pins and not notice it. Worth having a look?
poohbah - car starts well everytime, hot or cold, except it tries (and often succeeds) in stalling when very cold (i.e. the first start of the day).
bteoh - yes, I will turn my attention to the AFM plug next and check continuity on the wiring.
I didn't mention fuel in my list of possible suspects only because I have checked them thoroughly and nothing presented as a problem of out of spec. Plus, this is rich not lean which means I am getting good fuel delivery; either too good or not enough spark to go with it. Too much fuel can only be caused by a faulty ECU (swapped with no difference), faulty injectors leaking (been cleaned and flow tested weeks ago) or a sensor giving an incorrect reading that tells the ECU more fuel is needed than is actually the case. This is where I am heading now.
I should also mention the cars electrical system appears to be sound. I get 13.4V while running and 12.5V when stalled at the battery and similar figures at the ancillaries (except the fuel pump but I am not suffering form a lack of fuel! Plus fuel pressure is bang on all the time). So I don't think the issue is a lack of volts.
Have you changed the water temp sensor (and connections) for the ECU - sounds like it thinks it is cold all the time?
No, I have just been driving it as is recently. However, I have been thinking along the same lines and have bought a new temp switch but just need to set aside time to change it (it's not easy to access so will have to remove the intake plenum). Decided it is about time to change the coolant at the same time.
Hopefully I can report back on this in the next week or two.
Finally replaced the coolant temp sender to the ECU...and it made no difference. However, I did notice the wiring to the AFM is feeling a little hard so next step is to check resistance between the connector and the ECU plug and then see what readings I get when it is running. I'm tempted to get a pot and put it in line with the signal wires to the ECU for the CTS and AFM and see if I can 'fix' the problem by changing the reading the ECU sees. At least it would tell me if I'm on the right path.
It's frustrating because I just want to finish this and move onto the next thing to work on, replacing the clutch!
Has this got one of the old school Bosch airflow meters? There's a fairly interesting article on the net by a bloke going over one from a BMW bike (I think), he discusses the precision they were made with. Also he shows his careful relocation of the resistive tracks and testing setup. If nothing else it gives appreciation of how a hamfisted approach to tinkering with one, can really mess things up.
http://www.k100-forum.com/t11055-bosch-air-flow-meter-restoration-summary
Out of interest what spark plugs and heat range are you running? Would it be worth considering a warmer plug?
Henry.
Have already tried the warmer plugs but no difference. I have traditionally used Bosch FR5DC plugs and they run well but Bosch actually recommends the FR6DC so I have a full set of those that are fairly new. Didn't seem to make any difference and inspecting them they appear to be about correct.
That said, If I was buying another set I'd go the FR5DC as I never had a problem with them even on cold mornings.
I tested the wires going to the AFM today. Given the wire length (both from sensor to ECU and for testing) the readings seemed ok. I was getting 0.3, 0.4 or 0.5 ohms on every wire. Someone correct me if I'm wrong but I would think that should be fine and unlikely to cause significant problems. Next test will be voltage at the plug while the engine is running to see if load makes a difference.
After that, I am starting to get stumped. I would like to try the same thing with the CTS but not sure I can get access to that while having the engine running.
There is a small leak in the exhaust near where the O2 sensor is but again, I believe that shouldn't affect anything given I am running open loop at the moment. I disconnected the O2 sensor to double check and it made no difference as expected.
Personally I would try mixing some e85 into your tank (if application is compatible) and see if it runs any better.