Hello all, I’ve been having several issues with my mondial recently, the newest being a misfire which is stumping me. it started as a simple misfire which has been developing into all sorts of different issues. it seems to lose the rear bank at low rpms, as soon as you rev it’ll come to life and backfire badly due to the fuel build up at idle. I’ve replaced spark plugs and distributor cap, I’ve also tested a new coil. Would this be crank sensor? I’m a bit lost and confused now as there isn’t that much left? any ideas would be appreciated thank you
Also, I did start playing with the screw on the bottom of the throttle body, is there a set place to start with this as a standard and then adjust idle from there?
Sounds like you have a coil/ignition module on the way out. That's the guy that sits on top of the coils heat sync with the cover on top of it.
Don't disagree that the "ignition module" would be a prime suspect for losing a bank of ignition (along with the TDC sensor and the coil of that bank), but your memory is one generation off -- the QVs have the "ignition module" built into the Digiplex ECU. It's the follow-on 328/3.2 Microplex system where they got smarter and made the ignition module a separately replaceable part.
The screw at the throttle body is the air bypass. The warm idle should be about 1,000rpm. If you close the air bypass completely it should drop to about 600rpm. If that is the case, then your throttle plate screw setting is about right and it wont harm anything to play with the bypass to refine the idle speed. Being a bit on the higher side of the 1,000rpm is best for this type of fuel injection system. Did you replace one dist cap, but also the rotor on the bank that is cutting out? Any sign of arcing on the plug wire extenders? Are you sure you are loosing a full bank?
Only way that I know of is to send it to David Feinberg at Sarasota Italian Garage to have the internals replaced/updated: https://www.sarasotaitaliangarage.com/services/ However, if you can determine which bank is losing ignition, and then swap the Digiplexes or swap the TDC sensors (or measure the AC voltages from the TDC sensors at the Digiplexes when having the trouble -- it should be a small, 0.1~0.2V AC when the engine is running), you can better determine who might be the bad player rather than just throwing (rather expensive) parts at it.
... have you tested or replaced the HT leads/extenders? I have noticed the front bank HT leads to have a relatively short life span, probably due to heat from being in a confined space whereas the rear leads are being vented via the bonnet grill.
The early Bosch procedure (also in the Mondial 8/QV WSM) that got changed/evolved later. Also, the "balancing" doesn't/can't apply to a model with only one intake plenum (probably wrongly copied from something like a 400i procedure or some other MB/Rolls? model with two independent intake plenums). Probably OKish to do it that way only using throttle plate (but the idle speed will be more sensitive/variable to the unrepeatability of the throttle plate mechanism rest position -- the air bypass path has no moving parts).
Hi everyone, so I have had testers on the spark plugs to show when they are failing, and essentially it’ll rev freely if I raise the idle - but as soon as it drops to a standard idle it starts missing I’ve replaced the crank sensor which is towards the rear of the car on the side of the bell housing (I’m assuming that’s for the rear cylinders, closest to back of the car) and hasn’t really made any difference - if anything it’s worse. I’ve fiddled about with the connections to the ecu just to make sure they haven’t come loose - and hasn’t made a difference either. the only thing I have noticed is that the rev counter is a bit jumpy - does this come from a crank sensor or from the ecu? Im still tempted to put HT leads on but don’t want to just keep throwing parts at it any ideas what might be causing it?
The tachometer signal is created by one of the Digiplex ECUs. Just swap the connectors on the two Digiplex ECUs to see if the tach gets less jumpy (would be a bad sign for the Digiplex ECU with the connector that doesn't have the tach signal wire after the swap), or stays the same (a bad sign for the TDC sensor supplying the connector with the tach signal wire).
I’ve been playing around with the crank sensors, cleaning them up etc (the two I can get to) and cleaning the connectors, now I’m on 4 cylinders and got no rev counter reading, what have I done wrong now?
I'll try one more time Determine which bank has no spark (using a timing light or a spark tester). Swap the Digiplex ECU connectors: 1. If the same bank still has no spark = bad sign for that bank's TDC sensor signal. 2. If the other bank now has no spark = bad sign for one of the Digiplex ECUs. You can't just ignore one of the TDC flywheel sensors because it's hard to reach: Image Unavailable, Please Login PS This picture is mislabeled -- it should just be "RPM Sensor". The tach signal is created by one of the Digiplex ECU.
It’s bank 1-4 which is failing, looking at that diagram I’ve replaced the rpm sensor thinking it was for the 1-4 bank. interestingly putting the old sensor back in has no tach reading at all, the new sensor just jumps about completely off what it should be. I’ll swap over the ecu plugs and see if it changes
Right, so just swapped the plugs on the ecu, issues still exist the same (good news for the ecu I guess) so would you think the next thing to do is to replace the sensor for the 1-4 bank (the hard one to get to)?
Pop and bangs sounds like a fueling issue. I am having a similar situation with my Bosch K Jetronic on my 412. Sent from my MAR-LX1M using Tapatalk
Well, I feel like my lazyness and assumptions have failed me big time. swapped the new sensor I thought I had fitted to the bank 1-4 to the correct place as per Steve’s diagram and boom, running perfectly thank you all so much for your help. can’t believe it was the one sensor I didn’t check simply because I thought that was for the rear bank haha lesson learnt thanks again
The sensors are magnets, and don't generally seem to fail outright, they seem to cause poor or intermittant issue running conditions, I guess the magnetic feild wanes with time. I am curious, can you post an ohm reading on the old failed sensor?
I’ll post the readings this evening when I’m back with the car, it’s been intermittent for a while but only recently has caused the complete bank to fail, before it would just become an issue when you’re trying to park at low speeds - very annoying I’ll be road testing the car tomorrow too to make sure it’s still working well under load too
The stronger the magnet, the more it is sensitive to heat an vibrations. An engine bay is a terrible location for a rare-earth component.
No, this is an intermittent ignition fault. When the plug does fire, the fuel level has built up and BANG !
