95 993 C4 cab, the engine pings on fairly hard acceleration, worse when hot,I have tried Chevron injection cleaner and run Chevron super. My mechanic says there is no timing adjustment. The only way I can get it to stop pinging is to add a few gallons of VP112 unleaded race gas every few tanks. What's the fix? THANKS Bob

 

Any chance your car has an aftermarket chip?

 

Hi Bob:


Did your car suddenly just start doing this?

I too, would recommend that you look inside your ECU to see if you have an aftermarket chip. The '95's was socketed which made this easy to change.

Please let me know what you discover. I'll have some further suggestions depending upon what you find.

Its also possible that the dual-distributor internal drive belt has snapped and the "loose" rotor happened to have stopped and lined up on a cylinder. This is easy to check if you R&R the lower of the 2 caps and rotate the distributor shaft.

 

I second (or third ) the above comments about checking the chip. I had an east coast chip that knocked and pinged like mad. What a piece of....

 

Bob,

The simple solution is to move to a state that sells real gasoline rather than the crapoline we get in California. Since last summer we are limited to 91 octane garbage blended WITH oxygenates (sp?) like methyl tertiary butyl ether (MTBE) and/or ethanol. It's really pathetic... Every other state I've lived in allowed 93 or even 94 (Virginia) octane for far less than we pay. My local gas station charges $1.91 for "super"(??) unleaded.

I also blend a few gallons of 100 octane Unocal unleaded($4.05/gal) with the other garbage. I realize the 993's sophisticated engine management system theoretically makes this unecessary but it makes me feel better.

When I don't blend fuels I swear I hear a bit of pinging from time to time. It's not surprising, I couldn't light my barbeque with the stuff they sell at my local Chevron.

Sorry for venting. Good luck with your car!

Matt

 

This is a very bad trend. I had a tankful of 91 in my TT that caused the car to be way down on power. Changed to different brand and it was OK for a couple tankfuls. At that point, the car was sold and transfered to Scott. And I added some 100 that I had left when I gave him the car. He now tells me with his last fillup the car feels down on power.

I suspect some bad news - I am thinking that CA has further degraded the fuel. I no longer have anything that uses pump premium, but the CA folks should watch out and compare notes to see if this is a new problem. OUCH

 

Make sure you check to make sure the distributor belt has not broken...This always presents itself with detonation. It does not always throw a check engine light but can sometimes...I have had 3 different 3.6 litre cars that broke the belt and they feel down on power and detonate as the early symptoms. Never have experienced the late symptoms.....Very bad....

 

Hi:

Matt in SJ (H2ONOO) expresses a well justified frustration about the state of motor fuel sold in California.

I might mention that oxygenated fuels have been sold there since 1996 and the most popular oxygenate has been MTBE. While some folks have argued that MTBE is a carcinogen, there is no question about its suitability and superiority as an octane enhancer, compared to ethanol. If one blends enough ethanol into the gasoline formulation, its possible to maintain the same 92 octane level as the MTBE-fortified product.

The trouble is, the EPA has rightfully mandated that motor fuels containing more than 15% ethanol must be labeled and sold as Gasohol. So, at the current 10% level, the octane rating (R+M/2) will not meet 92 in most cases; hence the current 91 stickers found on the pumps. Believe me,...nobody would be pleased if 15% ethanol was used,.... That's another whole can of worms.

Mark D. also pointed out that using these 91 octane fuels can result in a distinct loss of performance which is quite true. All of these knock-sensor equipped cars will reduce ignition timing (and boost pressure in the case of turbocharged cars) to minimize detonation under load and in warm weather.

This places quite a bit of responsibility and extra work on the shoulders of chip tuners who offer performance-enhancing software. These people must offer a product that will make a power improvement using 91 octane fuels without triggering the knock-sensors that reduces output. Some East-Coast tuners have had some difficulties with this that has resulted in a net LOSS of performance.

The bottom line is that you simply might need to blend 100 octane unleaded racing gasoline when driving hard in warm weather or participating in driving events where maximum performance is expected.

 

Just to see how bad this creeping octane deficiency has gotten, I blended a half tank of 91 with a half of 100 sold at the 76 on Almaden ave in San Jose. Got about 95 oct per the formula on Steve W's website. What a kick in the pants difference, of course. Yet I have never experienced the dreaded ping, even under full throttle at low rpm. Must be something else going on with yours.

 

here in Santa Barbara county there are no!...race gas avlaible! I get to live on 91 octane!!!!!at least I dont have to pay for it!(bennys of working at a car dealership) <img src="graemlins/yltype.gif" border="0" alt="[typing]" />

 

To follow up to Mark's post: I filled up twice without adding any 100 octane and the car went from being rabid to merely quick. The second fill up was at a Shell station in Oxnard that I never used before. I felt no pinging under any conditions. Now, I am lead to believe the computer should back things off before we mere mortals could detect any kind of detonation.
I topped off with 5 gallons of 100 this weekend and the "Bitch Is Back" to quote Elton John.
My car is fairly comprhensively modified, so I expect Octane Sensitivity.

 

I have a '96 993 that I've had for the last 5 years. The car pinged badly on throttle originally, and even would have some hesitation. It didn't throw CE lights and I had no errors. Every time I'd make a change - like fix the gas tank vent, replace fuel pump, replace O2 sensors, and lastly replace the mass airflow sensor, the car kept getting faster and more responsive. Now the slight hesitations are rare, but they're still lurking. It's still pretty easy to get a ping on sudden throttle while the car is cold and feeling sporty.

The most noticeable thing that might be a clue is how the car feels great and like a sports car while the engine is cold. Just as it warms up, it loses perkiness and gets more dull on the throttle. It could be adaptation to pings, or it could be something engine temperature related. I just ran a tank of Techron at high RPMs hoping it can help a little, and it appears to not have had much effect. The distributor was rebuilt a few years ago and appears to be fine. Any thoughts? Could it be the cylinder head temperature sensor? Anything else I should test or replace as a precaution?

 

First of all, congrats on finding a 21 year old thread, thorough searching, that is to be 👏.
Steve ^ was the man, and he asked about potential ecu mods: Reading the above advice - and then considering the stuff you've tried or replaced, is there a chance your ecu was modified?
Again, just reading thro the above, octane booster is a cheap way to trigger a change/no change scenario that may help narrow decisions....

 

I can try 100 octane, but how would that narrow things down?

 

interestingly, the hammer reports that the ECU has 900 hours of engine running time, and the car has over 117K miles now. This suggests that the ECU was replaced at some point. The car was tracked (warped rotors in service records, paint chips on the hood), so I wouldn't be surprised if it was previously modified... How can I check if the ECU was modified?