I got a RPM question

RADARsx 2.0 · Post by **RADARsx 2.0** » Fri Oct 02, 2009 2:27 pm

Hey everyone I got an 04 sx2.0 (stock) automatic and it's got aprox 270k kms (167k miles) and I am wondering if it should be running at 2450rpms(+-10-20rpm) at 100kms/h (60m/h) and it runs at that at 50kms/hr (30m/hr)

Just asking cause I know my father in laws focus with the same siz motor runs almost 500rpms lower than mine..

Thanks for any input.

Post by **racer12306** » Fri Oct 02, 2009 2:28 pm

It's all about gearing. Someone with an auto will have to step up and answer.

Post by **occasional demons** » Fri Oct 02, 2009 3:31 pm

It runs the higher RPMs at 30 mph, due to the fact that it is not in O.D., and the TC is prolly not locked. Most ATX's will not shift into 4th until 40 to 45 mph.

RADARsx 2.0 · Post by **RADARsx 2.0** » Fri Oct 02, 2009 4:52 pm

Ok, well i don't have traction control on my car I think.

And the situation has developed about 10 min after I posted this.

I now have a missfiring issue and I have done the leg work and found that my compression is good (140 on all 4 cylenders) spark to all the plugs...and then checked the injectors and it seems that the #1 injector is fouled (not injecting right 50% of the time)

Got one on order (get it monday) This issue wouldn't affect the rpms at all would it?

JeffM · Post by **JeffM** » Fri Oct 02, 2009 5:06 pm

RADARsx 2.0 wrote:Ok, well i don't have traction control on my car I think.

TC = Torque Converter

And to answer you question: I would think if you were having an injector problem that it would actually drop your RPMs - not raise them.

SOKADAO954 · Post by **SOKADAO954** » Fri Oct 02, 2009 5:13 pm

JeffM wrote:
RADARsx 2.0 wrote:Ok, well i don't have traction control on my car I think.
TC = Torque Converter

And to answer you question: I would think if you were having an injector problem that it would actually drop your RPMs - not raise them.

canadian... eh?

esteinmaier · Post by **esteinmaier** » Fri Oct 02, 2009 5:17 pm

Nope. Ever ride a bicycle with more than 1 speed and try to push the pedals faster without travelling faster? That's similar to trying to change how fast a car goes at a particular RPM in a particular gear. Just doesn't work. I don't care if you're Peewee Herman and don't have any strength. It's still not going to make a difference in how fast your legs have to go to make your bicycle go a certain speed.

Post by **occasional demons** » Fri Oct 02, 2009 6:21 pm

JeffM wrote:TC = Torque Converter

Thank you sir!

A bad injector could raise the idle speed if it was leaking, but that would be the only scenario I can see it happening. Once the throttle is open enough to cancel out the IAC valve, I don't think it would have much effect, other than maybe a CEL if it was bad enough.
But IDK how much the throttle has to be open for that to happen. When My IAC failed, it would run @4000 rpm with the TB shut. So it could possibly run that high to attempt to correct the A/F ratio. A short in my Jeeps injector harness basically did that same thing. When all the injectors open, the idle speed gets a little out of control. Thankfully it only happened when I was wiggling wires trying to find another problem.

So the moral is, never under estimate how well the engine can run breathing through a straw. It is a weird feeling knowing the throttle blade is closed, and the engine is revving it's happy ass at you.

So I guess with an ATX, It could raise the RPM, only because it would have the TC unlocked, and would be utilizing it's stall speed. (That RPM rise when you mash the pedal, and nothing happens but engine noise, then you start moving a little faster.)

But like Eric said the RPM is not going to change, (unless the clutches are slipping). Once the TC stabilizes, it is going to remain the same ratio.

In your case if it is misfiring, the injector is not opening/opening enough, and would cause a drop in idle rpm, only if the IAC can't correct for it. It will definately cause a drop in power.

You really can't compare the rpm of one engine/trans combination to another, expecting them to be similiar, especially with an ATX. there are just too many variables. Hell even the exact same ATX combination will be slightly different, due to tolerances in the TC. At lockup, they should be identical tho.

RPM doesn't matter as much as matching the torque output for the specific engine, if it is running the same rpm as the other one. If it is not at peak torque/efficiency, then it really isn't a benefit. Even tho it is running slower, it will use more fuel, and have less power.

RADARsx 2.0 · Post by **RADARsx 2.0** » Fri Oct 02, 2009 6:57 pm

Ok. thanks. It's iddling at about 700rpm but occasionnally before this missfiring it would drop to 500rpm idle. (not all the time just once and a while)

I checked how it performed and it would respond farely well but gets to about 3000rpm when "stepping" on it and then it stumples over it's self.

I am almost 100% sure the injector is gone tho. I take it off and the car doesn't stumple more of less now. But take the plug wire or injector wire off of another cylender and she really starts to miss nad stumple at Idle.

It's a little wierd but i know compression is good and spark is good and the wiring all appears fine and voltages are fine...so it's gott to be the injector in my books.

But thanks everyone for the info on the rpms..so from what i can understand i seem to be just fine cause she is responding properly in all gears and ain't slipping at any time....so guess my car just runs at those rpms

excon · Post by **excon** » Fri Oct 02, 2009 8:30 pm

To answer your original question: yes, rpms should be around 2500 when you're doing 65 mph and at 30 mph you should be doing around 2000.

Weird trick though: when traveling between 30-35 mph, you can shift manually into "3" and you'll drop by about 300 rpms... Be careful though, if you forget that you've got it in 3 and not D, you'll hit 29 mph and it will downshift to second causing your rpms to shoot up to around 3000. It's also different from the next gear that engages ~35 mph because the rev range is completely different than the "3" gear...

Maybe mine is just weird. I'll try and record it one day.

RADARsx 2.0 · Post by **RADARsx 2.0** » Fri Oct 02, 2009 8:37 pm

I only have a 3 speed auto...1 3 and D...but when i shift from drive to 3'rd...it gets more rpms.

Post by **racer12306** » Fri Oct 02, 2009 8:40 pm

Nope, you have a 4 speed.

the 3 speeds go P-R-N-D-2-1

plus, all 02+ have 4 speeds.

RADARsx 2.0 · Post by **RADARsx 2.0** » Fri Oct 02, 2009 8:46 pm

Nope...mine goes P R N D 3 1

how is that a 4 speed frank? unless were counting R? (just curious cause the parts guy told me it was a three speed auto)

thats how mine goes. and it's an 04.

Post by **racer12306** » Fri Oct 02, 2009 8:49 pm

1 - 1st Gear
3 - 3rd Gear
D - 4th Gear

You can't put it in 2nd.

Sounds like your typical parts guy, aka a dummy.

RADARsx 2.0 · Post by **RADARsx 2.0** » Tue Oct 06, 2009 6:04 pm

Well finally got the part in from the dodge dealer (injector). I put it in, car ran like crap for about 5 min then ran normal but was spewing a bluish white smoke. no oil in the exaust that I could find and it didn't have the antifreeze smell. Went away after it warmed up.

But it sputered a bit when i took it for it's first drive. Is that to be expected? It isn't doing it now but just want to keep an eye on it and get an isight that someone else might have.