B-12 Chemtool jumps mileage on '89 525m

B-12 Chemtool jumps mileage on '89 525m. Never seen more than 24+mpg, even on way to coast with a 325' elevation drop from Raleigh, NC.

Ratty looking plugs and strange intermittent cyclic chugging until full temp plus 2-4 miles, led to B12 try. Prev experience with similar products like Techron and even the limited availability super stuff BG 44K, did not show much improvement.

Followed B-12 instruction of one can to 16g. Difference was 120 mi round trip at 70-75 mph. First 25m around 23.5 mpg then noticed avg improving. Reset and avg around 26 mpg and growing for next 10 mi. Reset again and mpg improved to nearly 27 at end of 120 mi run.

Interesting that there was no "chugging" from cold start at beginning all the way to 120 mi end of trip.

Return trip mpg grew to 29.8 for the last 50 mi. Maybe this is common for '89 525m, but it surprised me.

However, on return, 1/4 tank fuel level, the chugging that had been limited to cold start, first few miles, came on at 75 mph and persisted, intermittently, for about 20 miles. Off I85 to avoid traffic jam, we added about 8 gal of Exxon 93 and drove next 15 mi at 45-50 to avoid I85 traffic problem. No chugging.

Filled up with Conoco 93 and ran the 50 mi above with only a couple of very minor chugs. Next day the chugging was back with a vengance.

Sorry to be so long, but

1) problem is a real PITA with no solution in sight, and
2) Effect of running injector, etc. cleaner in fully hot engine for extended time, 240 mi here, may be a worthwhile report.

berryman's is going to improve your mpg dramatically while it is still in your gas. if you have that much of a problem, try two cans to a quarter tank for city driving, followed up by 1 can to half tank, followed by your oil change.

Was this a $3.69 injector cleaning?

maybe you have crud in your tank clogging your pump once the fuel gets low?

Quote:

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Originally Posted by Gene in NC

Was this a $3.69 injector cleaning?

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I don't know if that was directed at me, or to anyone in general. No, it isn't going to do the same as the on-car injector cleaner, but you can get pretty close (if the injectors are in serviceable, non leaking condition. Have you changed your fuel filter lately?

Fuel filter replaced recently.

Fuel tank appeared to be surprising clean when fuel pump recently replaced. That being said, the logic of sucking up something to temp reduce fuel flow is appealing.

Backing off on throttle to stop chugging and the rythmic/cyclic pattern add support.

That leaves chugging from cold start to warm up beyond full temp on guage unexplained, but will retest the 1/4 tank 75mph chugging ASAP.

I had my mechanic shoot some injector cleaner through a week ago. It feels maybe a little smoother but my motor has always ran pretty well. I had a weird power loss once since putting the cleaner through that I have never had before. I don't have the same symptoms as you but I'm posting because suspect mine is fuel related / m20 too. It is just the odd warm-start fail. It catches if I give it gas. Sometimes on cold starts it starts almost too fast and it feel like it nearly floods itself. It's not a huge problem but I feel like I should address it if it is fuel-supply.

I have always had this starting problem (among others) and along the way I have replaced the fuel pump, filter, and regulator. Before I replaced the pump I put in a check valve so now I have 2 check valves. All the ignition parts have been replaced at some point and I am pretty confident the air supply is good because it runs so well all the time.

Here is my next suspect... I think the crack in the return hose is new, I am sure I would have noticed that before, but it is definitely old hose so I am goint to replace them both.

***- is it possible that a tank vent is plugged and you are getting a partial vacuum in your tank or something like that?

Next day after the 240 mi trip running Berryman's the chugging from cold came back . After three days of that crap refilled the tank and CHANGED THE OIL TO M1 15/50.

ALL RUNNING PROBLEMS AND THE 1252 ( INJECTORS ) CODE WENT AWAY. Running clean.

Suspect may still be sensitive to low fuel level.

Acts flooded on cold start, lotta throttle reqd. and runs rough until cleared.

It could be failing fuel pump.