MFI sputtering/crapping out @ 3k ~ 4k...

[Danny_Ocean]

Just got my '71 2.4 MFI car on the road today. Appears to run fine with one exception. Under hard acceleration, at about 3k ~ 4k rpm, it kinda sputters/chugs. If I take my time accelerating, no problems. It will run smoothly and keep pulling. This only happens when I'm accelerating/pulling hard. Both fuel filters and pump are new. Tank was flushed/sealed and new screen installed. I don't believe it is a fuel starvation issue.

FWIW: Car sat for 15 yrs. I added some ChemTool B12 & MMO to the tank and ran it hard today for about 1 hr.

[Flieger]

MFI typically ends up on the rich side. How do your spark plugs look? Is there any black smoke while going through that rev range? You may want to look into an LM-1 air/fuel ratio meter for measuring AFR on the fly.

[Danny_Ocean]

No smoke (had someone driving behind me). Haven't checked the plugs. What should they look like? The air/fuel meter you mention...is it a portable unit or is it something permanently installed on the car?

[Flieger]

LM-1 can be bought on Pelican. It rides in the car with you.

Plugs should be a nice, light tan color on the ceramic. White is too lean/hot. Black or dark is too rich, too cold, or it may be carbon deposits from oil getting in through worn valve guides, etc.

[Flieger]

Jeff Higgins would be a good person to PM about the LM-1 operation and fuel mixture, spark plug diagnosis. He wrote the MFI thread about opening the pump for the mid+high speed screw mixture adjustment on the flyweight govenor.

[911st]

Danny,

Have you removed the pump or changed the belt?

The reason I ask is I built a 2.8 twinplug once with MFI.

It ran great to around 3500rpm then sputtered badly than ran well to red line.

After spending hours on it and having the experts give it a try, not one could figure it out.

It was a fresh RS pump and should have been great.

What happened is the pump was installed out of phase. I finally found this by removing plug number one and loosening the injector line at the pump and turning the motor by hand.

I found that when the fuel seeped out around the fuel fitting was not in time with intake stroke.

The other think is if the pump has sat for any length of time they can gum up and the rack progression gets restricted.

These may not be your issue.

[911st]

Thinking about it I may have removed all the plugs except number one to check the injectory timming.

[Danny_Ocean]

Originally Posted by 911st

Danny,

Have you removed the pump or changed the belt?

No and no. The pump and the belt are as they were when the car was "retired" 15 yrs. ago. I did all the usual stuff to get the car running again (plugs, oil, valves, filters, etc.).

Is there an easy way to check the pump timing? (Well..."easy" may be the wrong choice of words).

As mentioned, if I don't floor it, the car pulls nicely right through the 3k ~ 4k band. If I'm pushing it, I get the sputtering/flatness. Once it gets above 4k, it's smooth the rest of the way to redline.

[911st]

My guess is it is gummed up and the rack movement is restricted.

Most say you need to send it in to Guss and Pacific Fuel Injection in SF which will in the long run make for a better running car.

You may get away with taking it off, removing the side cover and flushing it with cleaner and working the rack.

[Zeke]

I had a '71 MFI car that I bought as a non running car. After going thru all the steps and getting it to run, I started in on the MFI. The ignition is the first place to start. You can't even think about the rest of the CMA until the ignition is spot on. The biggest one step improvement for me was new plug wires. They just don't live forever and I'll bet yours are way past due to be changed out. At least I didn't see where you did change them. Dwell and timing (full advance) are very important on an MFI car.

Let's take it from there if you still have the mid range sputter. Oh, and the belt timing is important, but the cars will run pretty well even 2-3 teeth off. It's something to look at for sure, but unless it's like 5 teeth off (like my friend's was), I wouldn't dive right in on that until you KNOW the ignition is perfect. BTW, this includes a full distributor service to make sure your advance is working properly.

Back to my friend just for laughs: his so called crack mechanic looked at everything on that car for over a year of in and out of the shop. The car ran well at low speeds, and since it was a Sporto, it mostly ran at low speeds (it was a T). But if my buddy wanted to juice it, it acted like yours. They finally found the belt timing was almost a full half gear off! Still, I say go for the wires first.

[Danny_Ocean]

I haven't got around to new wires yet. Did change the sparkplugs.

Timing is another issue. I can't see how to reach the distributor/set timing while the car is running. Is there a way to static time these

I should add it's a 914-6 clone. Distributor is in "front".

[Zeke]

Yes, you can static time it, but you do need to know total advance at 6K. Only way to do that is to put white marks on the pulley and use a good timing light. If you don't want to move the distributor while the motor is racing, don't. Shut it down and make your minor adjustment and recheck. You do need to know that the weights are moving. I'd get in that thing and give it a service that must be due after 15 years of sitting. You don't say if it's a T or what, but they all take a different total advance. The '72 should have a vacuum retard as well, IIRC.

I can't say from memory, but I think your 900 RPM timing is 4* ATDC. Better check me on that. Honestly, I would not set the idle timing and assume anything.

[tobluforu]

Biggest mistake I ever made was "thinking" that my car could run better. Low and behold the pump was 2 teeth off so I adjusted it. Wrong as the car ran much better when the car was off 2 teeth. No matter what I tried I could not get it to run perfect so back I went to 2 teeth off and it runs great.
I too have a A/f gauge that I use for 3 of my cars and the 2.4 mfi is a bear to get right even with that device. All logic, for the most part, seems to go out the window as the only way I can get the car to run great is pig rich. Also, with my car I could not get it to run good with NGK plugs and have been running the 4 electrode bosch plugs for years now. I have tried all sorts of plugs and configurations, but that is the only plug that works for my car. These cars have a mind of their own and what works for one may not work for others.
Plus there is no way I can get my car to run with the timing that it is supposed to run, so I advance the crap out of it. Basically I time it by ear. It seems like a lot of these mfi cars have "break-up" problems at that rpm. Time to CMA.
Heck, I just noticed your car has a 914-6 motor, so good luck and have fun.
Yes you can static time these cars, do a search as it is explained better then I ever could.
^^^ beat me too it.

[Danny_Ocean]

Originally Posted by tobluforu

Heck, I just noticed your car has a 914-6 motor, so good luck and have fun.

The car is a 914 with a transplanted 911 2.4 (T or E?) motor from '71. It isn't the 2.0 914-6 motor.

[Danny_Ocean]

Where do you shoot the timing light? I can barely get an eyeball in there to see what's going on. Can you mark/view the timing from underneath?

Originally Posted by milt

Yes, you can static time it, but you do need to know total advance at 6K. Only way to do that is to put white marks on the pulley and use a good timing light. If you don't want to move the distributor while the motor is racing, don't. Shut it down and make your minor adjustment and recheck. You do need to know that the weights are moving. I'd get in that thing and give it a service that must be due after 15 years of sitting. You don't say if it's a T or what, but they all take a different total advance. The '72 should have a vacuum retard as well, IIRC.

I can't say from memory, but I think your 900 RPM timing is 4* ATDC. Better check me on that. Honestly, I would not set the idle timing and assume anything.

[Zeke]

I didn't realize we were talking 914. Many have cut out an inspection hole in the firewall. You can't time a 914/6 very well without some mods. It wasn't easy with the 4 cyl, but there was a plugged hole in the housing to see the fan.

[Danny_Ocean]

Originally Posted by milt

I didn't realize we were talking 914. Many have cut out an inspection hole in the firewall.

Yeah, that's in the plans. Will make changing/adjusting the belt easier, too.