Marc arrived at my workshop unannounced on Monday morning. He told me about his car and its problems and asked if I could help. I knew about this problem Maserati from the forum and was happy and willing to help a fellow enthusiast who'd had more than his fair share of problems.
The diagnosis reported by Marc was overfulleling, following battery removal and filling up with Tesco's petrol.
I invited him to bring his car to my workshop at 8am the next day.
Marc had spent a great deal of time and money on this problem, having changed many parts, including sensors all over the engine.
I found 3 damaged spark plug leads, which I replaced.
When I started the engine, it revved to about 3000rpm for a few seconds before settling to a very lumpy idle and stalling. The spark plugs were sooted up. It was impossible to maintain revs, even by feathering the throttle.
I thought that maybe the knock sensor was giving false readings, causing the engine to cut out, so we disconnected it and tried again.
This time, the engine hunted severly, seeming like it had a huge vacuum leak, so off came of the air plenum to reveal the vacuum pipe from the manifold. It was not disconnected or damaged in any way, so it was reassembled it and I clamped off the pipe to the brake servo just in case the servo had failed. This made no difference, so it was time to think again.
With the throttle position sensor disconnected, it was possible to hold the revs at about 3500 rpm, so I thought that the problem may be with that component.
We traced back the wires to the ECU and found no fault, so suspected the throttle position sensor (TPS).
The only one which I had to hand was in my Ghibli. That was removed and fitted to Marc's car. We fitted that and it did seem to make his car run a lot better.
I knew that I was getting a 222 4v in for breaking the next day, and it was nearly noon (I had to leave at 1pm), so I suggested that we call it a day. Marc helped me with some bits and pieces and I dropped him off home.
The next day the 222 4v arrived and Marc helped me with attempting to start it until eventually we gave up and offloaded the car as it was.
With another similar car, it was going to be a lot easier to crack Marc's probem.
Marc substituted the TPS from the 222 4v, but desite the diagnosis, the engine refused to behave, so we were back to square 1.
We substutued the ECUs from the 222 4v, but they made no difference, so we then traced the wires back from the TPS to the ECU, but that all good.
We were running out of ideas, so screwed glass spark plug into #1 cylinder to observe the spark.
As soon as the engine fired, the mixture was rich, as you would expect, and sooned leaned down to give a healthy blue flame. After this, the flame became progressively weak, until the flame died, except for the odd random burn. This was associated with a slight rise in RPM. When the trottle was opened even slightly, the engine immediately stalled, so I concluded that the mixture was weak. As a corollary to this, Marc had observed that the engine would run well with Easy Start sprayed into the air intake. We decided that we may have an underfuelling problem.
It was close to 1pm again, so we decided that it would be best to leave it for today and swap out the fuel injectors from the 222 4v the next day.
The next day, when Marc arrived at 8am, he spoken to someone the day before, who had convinced him that it couldn't be the injectors, so we decided not to go down that route.
We were both stuck for ideas, but since Marc had brought with him a crankshaft/camshaft position sensor, we set our sights on getting the 222 4v running. The fault lay in the crankshaft position sensor and lack of electricity supply to the fuel pump. With these sorted, the engine soon settled down to a smooth idle. When the engine was up to temperature, I pulled off the connector to the air flow meter, the engine started to stumble, in fact it sounded just like Marc's at idle.
This was the clue to the solution. We substitued the air temperature sender, but it made no difference. We peeled back the wires on the back of the connector and tested for continuity to the ECU, but it was all good.
We then substituted the water temperature sensor from the 222 4v. No change, so we peeled back the wires on the connector to find them all frayed and maybe broken. When these were repaired, the engine failed to run at all when the plug was connected to the sensor, so we checked and re-checked the connections. All good, so what next?
The next in line was the MAP sensor. One wire was broken. This had to be it! Once this was repaired the engine ran just as it should. Marc was elated. I was glad too, because I don't like to be beaten.
All in all Marc's car was in my workshop for 3 days, with about 6-8 hours of time being spent on it, with Marc doing most of the the stripping out and me changing the steering rack on a Jensen Interceptor in between times.
I am glad have played no small part in getting another Maserati back on the road, and with Marc's help getting another Maserati running.
Duncan
