Twin spark motor woes

[Divano Veloce]

Hi all,

I'm posting in the 75 thread as its a 75 motor but installed in a 105.

When I bought the car the motor was wrong... no torque and it didn't rev.... I used this a a bargaining point when negotiating the sale.

On the first drive home had no torque, and when revved there was a rumble/vibration at higher engine/wheel speed. When home i peeled off the bonnet stripes and jacked it up to find 3/4 of a guibo. I also found that the VVT was permanently energised (with ignition on) but mechanically disabled.... With these things sorted I had no driveline vibration and loads of useable smooth and responsive torque up to about 4000 rpm. Beyond 4000 it became progressively less inspiring.

I now have a sorted 75TS on the road and it has no problem hitting the rev limiter and is delightful all the way to it. The 75 feels like it has less torque but I am fairly sure this is entirely due to the difference in gearing.

I thought I had found the culprit, a restrictive air cleaner arrangement adapted to the motronic AFM... which when removed did make a difference. But my experience at Broadford on the weekend is that there is still something very wrong above 4500rpm. The wrongness is no power and instead grumbling rumbling.... Goes away if next gear is selected.

I have started to suspect main bearings..... and will almost certainly pull the sump off this weekend and inspect.... any other areas of inquiry i should pursue???

[Divano Veloce]

Some suggestions I've received thus far include blocked or faulty injectors, fuel pressure, Motronic fuel maps wrong given that motor has extractors and may be breathing better.

I have observed the oil pressure and at idle its about 30 units (.1bar?) at 3500 rpm its about 50-60 units all when hot. When cold idle oil pressure is about 60-70 units. Oil pressure does not change with load which is apparently an indicator of worn main bearings.

[GTVeloce]

Hm, I would have thought any main bearing problems would be more evident at very low RPM. Personally I would be more interested in the top end of the engine. Assuming you have no issues with either distributer, I would be checking the timing chain for wear/slackness as well as that the chain tensioner is not at the end of its operation. Then I would have a look at the cams and again check for alignment (timing) and wear on the lobes. I'm thinking that as your revs rise, the valves are not opening or closing at the correct time and therefore you are losing your top end power. It could also be valve springs that have lost some of their 'springiness'. Not sure how to test that other than pulling them out which is a big job.

That said, I assume the static timing is bang on? Crank pulley; both distributers and both cams. Do you have the instructions for setting this? If not, PM me and I will send it to you.

[Divano Veloce]

Thanks Julian,

I did check the valve clearances, cam timing and chain tension when i first bought it, havent checked these since... Might be worth doing this as they're a bit easier to access than the main bearings....

I bought a 1750 motor many years ago that had been siting in a shed for many years. I installed it as a stop gap motor in my GTV and very soon after it developed a grumble/rumble whenever torque was requested of it. I pulled the motor and found main bearings 2 and 4 had starved of oil.. the crank galleries being fairly blocked with crud...  The berlina TS motor grumble/rumble symptom is very similar to what the 1750 motor exhibited, however the circumstances that it occur are very different - occurs at higher revs, not at higher torque.

[festy]

About the only advantage of the MAF is that adding headers etc doesn't require re-mapping because the breathing improvement is 'seen' by the MAF and the correct load point is calculated.

Based on your description, my first guess would be ignition - HT lead breaking down, faulty coil or ignition module, or bad wiring to the coil's LT side?

Have you checked for/cleared fault  codes?

[Divano Veloce]

Hi Festy,

thanks for your input. I haven't checked the fault codes on this motor/ecu since the diagnosing the VVT issue when I first bought it.

I have on hand three almost complete TS motronic motors to pilfer/swap parts from. I could do coils, ecu, injectors.....The fun part is testing.... I really need to get the motor to at least 5500 in 3rd, preferably fourth. Mr plod might not be very understanding....

[festy]

Actually, being a TS it shouldn't be a coil/ignition module/HT lead causing that (unless one of the ignition systems isn't working - have you checked?) but it could still be a dodgy power feed to the coils if they share any wiring.

Does your tacho jump around at all when you hit the problem? If it does, it could be the CAS missing teeth at high rpm due to misalignment or worn harmonic balancer - but I would think it would also do that just free revving because it's engine speed related and not load.

Other than that it could be something like a blocked fuel filter or failing fuel pump.
Is your alternator and battery healthy? It's not overcharging at high RPM?

[Divano Veloce]

Thanks Festy, brilliant! Would a wide band O2 sensor and cabin gauge be useful for diagnostics? Could you recommend one?

[festy]

Thanks Festy, brilliant! Would a wide band O2 sensor and cabin gauge be useful for diagnostics?

Yes - if it was a fuel issue that was going lean enough to cause a stumble, you'd see that for sure on the WB display.

But... an ignition issue can also cause lean wideband readings.
If the fuel from one cylinder isn't being ignited, the oxygen isn't burnt out of the mix and that's what the wideband measures.

If it's a fuel issue I'd expect to see the wideband start heading lean before the hesitation started, but an ignition issue would spike lean after the stumbling if that makes sense.

[Divano Veloce]

I wouldn't call it hesitation, it feels like the motor is making the power, but much of it is going into the vibration.. Its like the crank has its critical speed in this rev range (which it shouldn't). This is why i suspect main bearings as if one or more are gone as this will lower the critical speed... but it could also be the gearbox input shaft maybe the clutch/flywheel are loose? Stuff it I'm going to pull the sump off and have a look.

[Divano Veloce]

How does the ECU handle not having the vapor valve installed/connected?

[festy]

How does the ECU handle not having the vapor valve installed/connected?

I can't remember exactly what the impact is, but there's a code for it:

Code Select Expand


1-2-4-4         
a.Evaporation solenoid valve final stage short circuited to ground, or circuit interrupted.
b.Evaporation solenoid valve final stage short circuited to battery positive pole.

Check conditions: The malfunction is identified only during actuation of evaporation solenoid valve (sudden acceleration while standing, or engine under loads).


I vaguely recall hooking up a resistor to the evap solenoid wire to stop it from throwing codes...

[GTVeloce]

You may remember how much of a difference hooking up the solenoid valve (and charcoal filter) did to my car. Much smoother idle, better torque and generally smoother all over. The only thing it didn't seem to change was high end power.

[Divano Veloce]

Thanks guys!

When I last checked the fault codes I didn't get that one. My poor red 75 is going to get lots of bits taken off it this weekend (and even more once its on club plates....)

[Divano Veloce]

Given that I suspected main bearings I couldn't really go testing all these other things, potentially causing more damage to the crank and block. So I started with investigating bearings....

Number 4:


Number 2:


Although the wear looks fairly normal it is very localised but it doesn't seem to fit with the symptom, I was expecting worse.... I haven't driven it since Broadford and it seems to have leaked a fair bit of oil from the rear main seal so the motor will be coming out.

While its out I'll have the crank/block measured to see if there's anything fishy going on...