Sputters

[calbrat]

Right around 2000 to 2500 rpms my car sputters. Normally this is on the freeway at 50 mph. This isn't a real big problem but irrating if I try to gun it. It doesn't happen all the time either. The problem is more apparent now since I put a racing muffler on the car, which seems to have lower rpms at higher speeds. For example, at 3000 rpms I was going 60 now I am at 68 or so. So at 62-63 mph I am in that rpm range where the sputtering begins.
What do you think? Injectors? Intakes? Throttle?
Steve

[scotty914]

well the speed change is impossible everything is a solid connection there is a direct relation between rpm and speed and it not change unless you change gears

now with the sputtering i think that is the throttle postion sensor i think you can check this by disconnecting it ( i own a 1.8 not a djet so i am probably wrong )

it could also be the mps but dont ask me

[calbrat]

Uh... I am not seeing things... the car is FASTER!!!! And at lower RPMS! Something changed and that's all I did was change the stock muffler to the racing one. More HP I think has a direct correlation to it!! I changed the tire size last week but I discovered all this before that. And actually the tires aren't as tall so hypothetically, my rpms would go higher at a different speed. If threw 35's on for example I'd tach out at 4000 at 65, (I would guess) instead of the 75 series tire I had on before. Tire size though is different than raising HP by putting a high flow muffler on. The engine doesn't have as much resistance.

[Dave at Pelican Parts]

The speedometer gets its reading off of the transmission. It doesn't "know" anything about the tire size, it just "assumes" a given size.

The clutch connects the engine directly to the transmission. A given gear always has the same ratio of input speed (RPM) versus output speed (wheel speed).

The only ways you can drive a different speed at the same RPMs, are to change gears or slip the clutch.

Your speedometer reading may have changed (did you mess with the speedo cable??) or your tach reading may have changed, so it may look like you are going faster at a given RPM. But that isn't really the case.

If you swap a good quality muffler on for the stocker, you will get up to that speed faster. And that's the point, right? Get to whatever speed faster than you used to...

Check the ignition system thoroughly, check that the fuel and vacuum hoses are routed correctly and not leaking. Check compression and also fuel pressure. Then start checking the FI components. Which FI system do you have?

--DD

[calbrat]

Interesting...

Noticed the different RPM reading at speed, immediately after leaving muffler shop!! I just changed the tires from 165/75's to 195/65's a month or so later. My car is taching consistantly lower at 65 mph. I had the problem with the sputters starting at 2500 rpm when I was going let's say 53-55mph, and nowI am almost 60 mph, which made the problem more noticeable near top speed on the freeway, or going 60 down country roads because I am taching down there now. You are telling me this is impossible and I want to believe ya, but... this is what's happening!

I have the stock injection system on a 74 2.0 liter. I tuned up the engine about a year ago. Installed new muffler mid July

[campbellcj]

Your tach may be malfunctioning. The connection at the coil is just a little crimp connector that can work loose easily. If it's loose but not totally off, then your tach needle will swing and bounce.

[Dave at Pelican Parts]

Unplug the throttle position switch. The car should run pretty well without it, though the idle may get worse and acceleration will suck most fearsomely. If your sputtering goes away, then the throttle switch probably needs replacement.

That's one of the classic D-jet wear problems.

For good D-jet info, see http://www.914fan.net/djet.html .
For just about all the info that exists anywhere, see http://members.rennlist.com/pbanders .

--DD