Will Engine Run Smoothly On Only Front Bank?

I know it will not run smoothly on the rear bank of cylindars because one of the connectors came loose just dangling there. Almost undriveabel. Recently, however, after warm up the car, and although running quite smootlhy, had WAY low power. Then suddenly ran normal as if four more cylindars kicked in.

1) One possibility crossed my mind: That there might be a timing retard temperature sensor.

2) Another possibility is the front bank of cylindars simply has an intermittent bad connector. I have jiggled them around but still experience a short power drop off once in a while of very short duration. The ignition modules are not all that expensive and wonder if it is worth while just switching it out.

3) On the other hand I know there are a series of timing sensors that might be a problem. Are these sensors difficult to replace?

Even if the problem becomes permanent there probably would not be an issue of needing a tow to get home, and it happens rarely to begin with. Just wonder if anyone else has had such a problem?

 

1986 QV coupe US spec

 

Hi Steve

My appologies for inadequate identification. I live in the US. The logo on the back of the car reads Mondial 3.2 QV. The door sticker lists March 1986 manufacture date, and the emision sticker in the engine compartment lists California Spec 1986. Registration is 1986.

I will search on TDC flywheel sensor as you suggest. However, I know the car woud hardly run when the front bank was entirely disconnected by the dangling connector. Yet in these latest episodes the car ran entirely smoothly without bucking, chuging or other indications to me one entire bank of the car engine was not firing. Just very low power that suddenly re-emerged.

And so I speculate there may be a larger timing issue but since I do not know these things I am hoping someone might explain how it could run so smoothly yet so weekly. Hence the question whether the entire front bank failing would be any smoother then the entire rear bank failing which made the car almost undriveable. Thanks to all who might have some speculations on the matter.

My research so far indicates there is such a thing as a 'timing switch' but not enough elaboration on what or where that is or what it does. I hope my search on TDC flywheel sensor will elaborate but I am open to any and all speculation.

Once again Thanks!

 

After reading up on my 3.2 I learned (maybe):

1) It has a single timing sensor.
2) It probably has a limp home mode.

One possibility is the car is slipping into limp home mode from time to time due to bad timing sensor connector or bad sensor itself. The problem is so rare, and the car is so drivable when it happens I plan to wait till the very intermittent problem becomes more chronic.

I have gone half barking dog mad at times with intermittent problems. I remember my Z-28 battery would go dead if left sitting for a week or two on business trip. Turns out the hood light never went off. One of the few times I took the car to the POTC GM shop(Pirates Of The Caribbean - DC Branch Office) and they managed to find it right away. I can tell you why my reluctance to use these people for anything.

Specifically, I took my 5 liter Z-28 HO 5 speed to Summit Point for track day and got fuel starvation in second gear. Took the car to POTC and was firmly told my 5 liter, HO Z-28 5 speed was not intended for such driving and forget about it.

I determined the in-carb itty bitty fuel filter that quadrajets alway have had now had a return fuel check valve restricting the flow. A sharp pencil fixed the problem. GM subsequently had a recall and fixed the problem by adding a SECOND fuel pump in the gas tank to jack up the pressure. I never bothered.

 

Our mechanical constant flow fuel injection, to my knowledge, does not have a 'single bank' cut off, though I may be wrong. Assuming there is no single bank cut off I now have some evidence my car is going in and out of limp home mode.

Why do I come to this conclusion? One time this problem apparently lasted from start-up to full warm with a total of about 5-10 minutes. Much of that was at full throttle up hill at 4,000 rpm in fourth gear which is when I noticed how weak was the engine power.

And why did I not notice this problem earlier? One reason may be the timing map I noticed during my research. The very bottom map shows very little timing advance below 3,500 rpm OR above. In fact, ALL of the other timing maps show a sudden timing bump at 3,500 rpm.

Accordingly, just driving along with light throttle shifting at even 3,000 rpm on level road might not be all that noticeable. And now into a non-sequitor: Why the odd timing curve? I have done lots of timing on my suppercharged cars and in every case these cars could vigorously tolerate lots more timing below 3,000 rpm then above. So I installed a boost timing retard system

One of the things about the Ferrari engine that has baffelled me from the beginning is the relatively smooth torgue curve all the way down and all the way up. One way to smooth out the timing curve, while still leaving full power at the top is to torgue manage through timing methods at lower rpms. Front wheel drive cars often, I believe, do torgue management through timing to reduce torgue steer on hard take-off and at hard shift out of first gear. Another reason for short timing might be emissions control in the test loop.

One thing I did not notice during my full throttle at 4,000 rpm was any sort of rotten egg smell from rich condition. Further, I did not notice flames or smoke or untword fumes of any sort issuing from the rear of the vehicle.

Just speculation - till I get full failure and can reliably diagnose the problem without a lot of curse words. I am just pulling speculation out my butt, but speculation did Isaac Newton little harm.

 

PS More Speculation

The two valve Porche of the era had a VERY pronounce torgue jump at about 3,000 rpms. Disconcertingly and potentially dangerously so. A smooth transistion to full cam power is very much a good way to help provide docile handling characteristics.

I love playing like Isaac Newton!

 

Hi ME308,

I do over think things but find it fun to do and appreciate critical commentary as part of the package. The problem has not recured but if it becomes a serious inconvenience I might simply replace both units if I can not isolate which bank is misbehaving.

 

I Love This Forum! My own speculative ramblings lead to an actual plan of action.

Thanx Guys!