So im having this issue and im normally pretty good with diagnostics but cant seem to come up with this one. when my car is cold or after sitting for a good amount of time when i drive off i can run say 70mph in 5th gear at 2k rpm but once ive been driving for a while and its heated up i will be running 45 to 50 in 5th gear at 2k rpm. this really sucks because any time im out on the highway and should be gettin good fuel consumption im actually getting terrible gas mileage because im running 75 mph at 3k rpm instead of right around 2k. Any ideas? Im stumped!
Also not sure that this would effect it as it never did before but my cel is on due to insufficient egr flow(aka i need to clean my egr passages)

 

What Is Insufficient EGR Flow? | eHow.com
It sounds like a good idea to start there and get rid of the CEL.

If the problem still exists:
When was your last tune up?
Have you cleaned out the throttle body and IAC yet?

 

As GP advised, check for codes. There could be a trans code stored that will provide a clue.

My 94 EX runs about 2300 at 60 mph in lockup from memory. 3K at 75 mph doesn't sound too far off. I have an excel spreadsheet (mainshaft rpm vs. mph) that I put together when I had a torque converter lockup on a 2.5TL. PM your email address and I'll forward if you want.

If you know overall gear ratio (from specs in manual) you can calculate how much "slippage" is occurring. If you have a P0740, the Torque Converter is not locking.

A quick check suggests that 75 mph = 2900 rpm w/ zero slippage. This is based on 94EX specs I have; 0.674 for 4th and 4.133 differential reduction.

good luck

 

TX, he has a stick shift?

I'm with the CEL being on. Cold and before going to closed loop the "rpm's" seem fine, then once into closed loop they seem to be off....just me.

 

Thanks, I missed MT.

I recalculated based on MT 5th gear ratio (differential ratio is same) and this indicates 3K at 75 mph is correct. Note, this is from 94 accord manual.

good luck

 

this is a manual tranny - fixed rpm to mph ratio.
so the above suggests that either the speedometer or tach changes accuracy with temp.

my '92 5 spd is 3000 rpm somewhere around 70mph in 5th gear

 

If 3k at 75mph is normal, 1) why when its "cold" does it run so much "better" aka 65 at 2k and also 2) why do i get such GREAT fuel mileage at 2k but such HORRIBLE fuel mileage at 3k? i just dont get it, there is something im missing unless because at it "heats up" it builds more exhaust gasses over time and the fact that the egr passages are blocked it cant recirculate properly and that is whats causing the issue. Thats the only thing i can come up with right now and like i said earlier i feel like if thats not it then there has to be something im missing.

 

At 65 your rpm should be about 2550 rpms.

Either your mph is reading high (you're going < 65) or your rpm is reading low (your going 65 but rpm gauge is low). Suggest checking your distance traveled over 6 minutes on highway, using mileage markers as a cross-check. Multiply mileaage by 10 to get avg mph over 6 minutes. This should determine whether MPH or RPM gauges are incorrect.

good luck

 

I'm back to closed loop vs open loop.

You have a stored code, I'm for addressing a known issue before getting into others that are not cut and dry.

 

yeah im going to be taking care of the the egr passages any day now.

so on my to work this morning

As you can see here i was doing 60 mph at 1750 rpms, so had i been able to increase my speed to 65 i would have been running 2k rpms, on my way home tonight as i neared my house (on the same stretch of road) i found myself running 55 mph at 2250 rpms. Ridiculous! something is definitely going on here and im missing something thats causing it. I just cleaned iacv about 2 or 3 days ago but im noticing that sometimes when stopped in neutral no clutch i idle at "750" rpms and sometimes (seems like when warm) idling at 1k?

Is my iacv acting up? does this have anything to do with this other issue?