1991 spark knock...

[Tiggie]

My mom's '87 T-Bird 5.0 has had spark knock issues since it came off the lot brand new. It's always required mid-grade. It depends on the car, I guess.

[Pirate]

OK, Got a slight problem with my 91... Want to see if anyone can give me a clue as to what is the problem...

When it is under 70 degrees outside... my car spark knocks like a bitch... And gets worse if I idle for a few minutes... Or turn a right hand corner... Then it sounds like it is about to blow up! However, when it is warm outside... it drives perfectly normal...

I have checked the computer for trouble codes... No codes in the computer, no warning lights... and the timing is right on the money... (And has less than 10,000 miles since the timing chain was replaced)

Any ideas???


Tom....

Some ideas....

1. Check the vacuum advance line routing from the carb, to the temp switch, and then to the distributor. The temp switch is supposed to either kill vacuum when it's cold, or advance it, depending on the setup.

2. Check water level in the radiator. Right-hand corners are pulling water away from the temp switch that sits up high on the intake..on the right side of the engine.

3. Check your vacuum advance. It may be that it's going bonkers, I can recall a 351C I used to own that would go 90-degrees advanced with the broken vacuum canister on the duraspark distributor that I installed into it...

4. Concerning everyone else with pingning issues: The 10%+ ethanol is only a hint at the future. These older engines are going to need more fuel pumped in, as ethanol is nowhere near as powerful as regular gasoline....

5. Run colder thermostats. Drop them to 180-185-degree units. Heat and ethanol don't get along very well. It might very well be a good idea to look at monkeying around with resistors to trick the computer into thinking it's running hotter, also...this isn't advice here, it's merely an idea.

[gadget73]

I believe he has an EFI 5.0 in his 91, no carb or vacuum advance.

[Pirate]

I believe he has an EFI 5.0 in his 91, no carb or vacuum advance.

Sorry, I thought he had the 5.8 in there...

[trwp72]

Nope.. Stock 5.0 F.I. I WISH it had a 351!!! Still it runs pretty good... just the damn spark knock driving me nuts... Oh well, it is getting close to summer... At least it won't be doing it until next fall / winter!


Tom...

[Pirate]

Nope.. Stock 5.0 F.I. I WISH it had a 351!!! Still it runs pretty good... just the damn spark knock driving me nuts... Oh well, it is getting close to summer... At least it won't be doing it until next fall / winter!


Tom...

Right hand turns, correct? It does this in right-hand turns?

If there is an air pocket by the coolant temp sending unit, water would pull away from the sending unit in right-hand corners...if I recall correctly, it's on the right-hand side of the intake...but I don't understand the pinging issue, if anything, it would try to go into cold-running mode, and back off timing....

I begin to wonder if you don't have water or oil pooling up in the intake manifold log after the engine sits, making right-hand turns could theoretically move fluid toward the intake ports, and try to cause hydro-lock in a few cylinders...

Just for giggles, I might recommend replacing the coolant temp sending unit, if it hasn't been replaced already.

[trwp72]

That is one thing it does do... but not all the time... I drive about 10 miles from work, and there is one corner going onto the interstate that it does that... (45 degree turn, slightly banked to the right) it spark knocks like a bitch, blows smoke out of the exhaust... And then after I REALLY get on it... it straightens out, and it quits smoking... Another time it did it after I sat idling for a while while going through a car wash... (One of those wash and go places where you stay in the car) The smoke is sort of grey, and alot of it for about 4-5 seconds.. Then it clears up, and quits spark knocking... Of course, come to think of it, I turned right out of the car wash... maybe i will get a new sensor this payday, and see what happens.... Tom...