[Paul S]

Have done a search but nothing jumping out at me.

Been having a tinker with our 2005 Quatroporte project car, it was bought with a known issue of not firing on all cylinders. Did a compression check and cylinders 5-8 are running around 120-125 on the gauge on a cold engine, where as cylinders 1-4 are down to around 25-50.

So a slightly puzzling one, all 4 plugs are light grey and dry on 1-4 and black and sooty on 5-8

Given there is some compression and also level of consistency with each bank its a bit of a weird one.

So throwing it out to the good people of Maserati life to see if anyone else has has similar in the past with this engine?

Possibly thinking a blown head gasket on the one bank that is somehow affecting all 4 cylinders, the engine is holding water though and no mayo in the header tank, but it could be misting, blowing out the spark and then heading out the exhaust.

 

[Paul S]

Thanks for the reply, I dismissed that as we do have compression, although low. If valves were opening at the wrong time, there would be no compression at all?

 

[Paul S]

Good to know that about this engine, thanks Jason. Will do. Battery died, so recharging that and may put a drop of oil into the tops of 1-4 to see if that ups the numbers at all, more for curiosity than anything.

Would a dodgy variator on these engines alter the timing sufficiently enough to allow the valves to be open ever so slightly early or late on the stroke, preventing a full hit of compression?

 

[Paul S]

Some very interesting stuff, thanks gents.

Will give feedback once I am back where the car is stored.

 

[Paul S]

Small update, but I also thought some background info on the car would help as well.

It was purchased directly from a salvage dealer, who had also directly bought it from the last owner.

No damage, but was advertised as miss firing and needing attention.

We were on the look out for a mechanical donor for a future project build, so as long as the engine was not seized we were willing to take a punt, and the asking price was reasonable.

Deal was done before inspection as it was on ebay and we did not want to lose the car, plus the dealer had good long term feedback.

We arrived with our trailer after a 3 hour drive to find it had a flat battery, had not run in months and was low on fuel. They did manage to get it to turnover but it ran like a bag of nails, but as the engine was moving we were ok with the condition.

The depot manager told us the verbal diagnosis had been blow back into the inlet manifold, but there was no supporting paperwork confirming such. Unusually for a mechanical fault car, the engine was all buttoned up, all covers in place etc, where as normally they are partially dismantled to a point where the fault is found and the customer calls a halt to further works due to cost etc.

Anyway this was a few months ago.

Over xmas we had a few clear days so decided to start investigating, first thing was engine covers off, undo coil lead covers etc which was not easy as most here will know how buried under the bulkhead this engine is on the Quattroporte, then coils off and start taking out the plugs to do a compression test.

We get to cylinder 6, whip plug cap off and go to undo the plug, only problem is there is not one fitted!!!

Weird I think, given everything had been put back together, but assume this is the offending cylinder.

Compression test then done, and further weirdness as bank 4-8 seems ok inc the one with the missing plug, where as bank 1-4 is well down to 25 in places and a max of 50 psi.

So this is how the thread started........

Anyway the update. The car is standing in its final resting position where it will be stripped in the coming months, but it would be nice to get the engine operating fully before then. New to this engine, and no access to diagnostic kit or even a leak down tester at the moment, so its all relying on old school "suck, squeeze, bang, blow" for now.

No local stockist of the required spark plug, so decided to oil cylinders 1-4, put one of the plugs from that bank into no 6 so at least one bank is potentially functioning, plug the missing plug hole with the compression tester and see what happens on a fresh battery.

She wanted to run, banged and farted a bit but would not catch, so off for some fresh fuel and try again.

Wham she fired straight up and once warm was ticking along nicely on 7 cylinders, and the compression tester was showing 150 psi in the 8th cylinder, where as it had been 30 ish before

Spark plug now on order to see if we can get all 8 firing before the dismantling starts.

Guess we will never find out why that plug vanished, sabotage for non payment of a previous repair bill maybe, who knows. I assume that standing for so long, plus old fuel etc caused the low compression in the one bank so the engine was probably only running on 3 cylinders in the end, the extra plug then allowing the second bank to fire correctly, a bit of oil dripped into the first bank, sealing up the bores to get them all firing again plus a squirt of fresh fuel may have all helped get the compression back up to normal.

Will do a final update once the plug is here, fingers crossed that is all it was in the end.

There seems to be little info out there for the DIYer/project builder on the Maserati version of this engine so I am thinking of starting a separate thread to try and pull together the known info with regards its potential abilities when used in alternative vehicles. We do not have the option of crate engines in the UK/Europe and these Maserati engines are now becoming plentiful and affordable so seem to be a great alternative, they appear strong, well engineered, and have most of the bugs ironed out now, and have the potential for much more power given what Ferrari get out of them in the flat plane version.

Ours is going in a track truck, standard to start off with then possibly a pair of turbos, fairly low boost as we want to remain at standard compression, it is not going to be a money no object build so most components will remain as factory. It will weigh half that of the Quattroporte though which will also help push it along a bit better.

Oh if anyone in the UK or Europe is in need of a complete undamaged bare bodyshell with all associated painted panels such as doors, bumpers etc etc and all glass still fitted, or a complete cream leather interior give me a shout by PM as its all surplus to our needs. Also lights, airbags are available.

Probably ideal for rebuilding using a structurally damaged donor car, it is HPI clear and comes with all ID/V5 registration document, service books etc

 

[Paul S]

Next update

Errant spark plug fitted and she fired straight up, ran a bit notchy still but slightly better, as soon as it got warm though it did not want to rev, and I noticed combustion gasses coming up from underneath banks 4-8 so I guess plug 6 was left out for a reason after all. Assuming the last owner told the garage just to button the engine back up rather than carry on with a repair, and they left the plug out to indicate where the issue they found was located.

Seems to be narrowing down to a head gasket issue in my mind around cylinder 6. I cannot get underneath the engine where the car is currently located to see exactly where the gasses are coming from. The low compression on banks 1-4 was probably a red herring due to the car standing for so long, once warm the compression was up over 150 psi again in that bank.

Next step is to pull the engine anyway in a few months time, so just before doing that will take a peek underneath to see if I can spot the combustion gas leak.

Engine will have a top and tail refresh as part of the transplant into the project vehicle, but it would be nice to narrow the problem down prior to that.

Thanks all for the input.