Old BMW and SI-1 -what should I expect?

[Russell]

Glennc, I am using about 1 to 1.5 oz of SI-1 per 10 gallons of gas, usually 93 octane Chevron, BP or Shell. Temps in 90s now and car seems to run rather well. Fill-up to test with OBC Is seldom fill up anyore -too painful! good idea for a test.

 

[Johnny]

I emailed Red Line about adding some at each tank full Vs the method that I have been using of just pouring in a bottle every 4-5K. Here is the reply I received from Dave.

Johnny,

Thank you for contacting Red Line Oil, the maintenance dose is about 1.5 ounces per 10 gallons of fuel. Ideally it should be used on a continuous basis, for continued lubricity, to maintain the injector cleanliness as well as working to clean intake valve in combustion chambers.

Regards, Dave
Red Line Oil

 

[severach]

Originally Posted By: glennc
That makes sense, since it seems reasonable that a dirty injector would deliver a bit less fuel than the computer thinks it will be delivering.

An injector bank delivering less will be corrected by the oxygen sensor. Dirty injectors flowing different amounts can be partially corrected but at some point the PCM must richen for safety.

Quote:
The combination adds about $0.90 per fill-up. Not totally inconsequential, but less than the difference between top-tier and other fuel, for example.

Around here all fuels are the same price. Parking lot tail pipe scans tell me that Top Tier or not there's not nearly enough cleaner in any fuel brand. Premium might have it but regular sure doesn't.

 

[glennc]

Originally Posted By: severach
Originally Posted By: glennc
That makes sense, since it seems reasonable that a dirty injector would deliver a bit less fuel than the computer thinks it will be delivering.

An injector bank delivering less will be corrected by the oxygen sensor. Dirty injectors flowing different amounts can be partially corrected but at some point the PCM must richen for safety.


Continue your thinking one more step. The O2 sensor corrects and tells the injector to fire a bit longer, to inject the correct amount of fuel. The on board computer thinks that the actual amount of fuel that is being injected is the slightly larger amount that would equate to the slightly longer open time. Consequently it calculates a fuel economy that is slightly less than what the car is actually getting. When I fill the car up, I can track the difference between the actual FE and OBC FE.

Originally Posted By: severach
Originally Posted By: glennc
]The combination adds about $0.90 per fill-up. Not totally inconsequential, but less than the difference between top-tier and other fuel, for example.

Around here all fuels are the same price. Parking lot tail pipe scans tell me that Top Tier or not there's not nearly enough cleaner in any fuel brand. Premium might have it but regular sure doesn't.

I tend to agree. The same line of experimentation that I alluded to here has shown me that whether I use Shell gas or non-detergent off-brand gas, the same results occur at about the same pace. I have to use an added cleaner to keep the injectors clean.

I suspect the major-brand fuels do have cleaners in them, just very small amounts. Enough to keep things from getting crudded up badly, but not enough to keep things squeaky-clean. Maybe, wild guess, 1/10 the maintenance dose I'm now using or something like that. This jives with some old posts here from tanker drivers saying that detergents are added to the fuel at the depot, but in "very small" amounts.