19mpg on the interstate. Loss of power at high RPMs.

[Sulaco]

As the title implies.

I hooked up my bluetooth OBDII interface, loaded the torque app on my phone. I wanted to check my highway mpg. My city mpg has been hovering around 14mpg. I thought I would get something more normal on the interstate at 75mph, but no. Could not break 20mpg! When I first got the car, it was getting almost 30 on the highway and about 22-24 in the city. Also, I've noticed a drop in horsepower in the higher-rpm range. If I give it full throttle, it feels normal until about 3.5-4k RPMS, then the power doesn't increase anymore at all. The RPMS keep climbing and the speed keeps increasing, but it's definitely got a serious issue delivering the available HP it's always had at those RPMs.

I understand it's an old car, but maybe there's something I'm missing. I doubt it could lose compression to that extent, that quickly. It does have the original throttle body, and the MAF is about 8 or 9 years old. I've done head gasket, wire harness, plugs and plug wires (recently), o2 sensors (recent), fuel filter (recent), engine vacuum lines (recent), and some other things I can't remember off the top of my head.

Could something be causing a rich mixture which also results in a loss in power? Help?

I think my signature has it wrong. Now it's up to 250k miles. It still purrs like a kitten!

[SD202]

Cats, When have they been replaced ? The packing is bad around 200k . check those out next. Did you inspect the fuel pump when changing the fuel filter ?
IF the cat is the culprit you luckily live in a state where you have no SMOG testing and Ca Air and resource board to deal with, You could cut out the factory cats and weld up some fresh ones.

[Sulaco]

ugh. cats. dont' they cost like $1500??

[strictlyspeakin]

Can your bluetooth interface track if the car is running rich or not?

[Sulaco]

I'm not sure. I'll definitely check on my way to work tomorrow.

FYI, it's getting 14mpg city.

Also, my timing chain is factory original. Fun fact.

[Sulaco]

Cats, When have they been replaced ? The packing is bad around 200k . check those out next. Did you inspect the fuel pump when changing the fuel filter ?
IF the cat is the culprit you luckily live in a state where you have no SMOG testing and Ca Air and resource board to deal with, You could cut out the factory cats and weld up some fresh ones.

you mention inspecting the fuel pump. as far as I've always known, a fuel pump doesn't really ever perform poorly. it either works or it doesn't. is there something I'm missing?

[benzfan]

Don't look for fuel delivery issues when the mileage is poor. I would go after the exhaust restriction every time when you see a loss of high end combined with low mileage.

[202brabus]

You have a bad MAF sensor, Replace it (even with a cheapie unit but it wont last long) Happened to me. I got a code for fuel trim. It would hesitate after 3.5k RPM's if I romped on the gas pedal. Im 99% sure that's your problem

[Sulaco]

It's not hesitating after 3.5k. The power just seems to hit a plateau at that RPM. Plus, has only been throwing 1 code for the last year: clogged EGR.

[strictlyspeakin]

Did a quick google about clogged EGR. Several sources there mention the your symptoms.

Have you checked this thread about cleaning it?
http://www.club202.com/forums/showthread.php?10843-P0400-Egr&highlight=EGR

[Sulaco]

Did a quick google about clogged EGR. Several sources there mention the your symptoms.

Have you checked this thread about cleaning it?
http://www.club202.com/forums/showthread.php?10843-P0400-Egr&highlight=EGR

Very interesting, indeed. This kind of revolutionizes what I thought about the whole point of EGR. I thought it was some misguided attempt at being green by making engines recirculate exhaust gas (and thus robbing them of MPG and HP). I apologize for the way my brain works.

FYI. When repairing my A/C evaporator, I found a far easier way to remove the EGR pipe on the m104. I'll clean it and see what happens.

Then I tackle the gummy, slipping, flaring transmission. 200k miles on a rebuilt tranny that's never had a flush or fluid change. Even if it's a total loss, I can't really complain. Plus I have spare everything on my parts car.

[strictlyspeakin]

It can't hurt to clean it. You know that your car is throwing that code. I did read that it might be good to see if it the EGR valve holds vacuum first in case that's the problem before you set about removing it.

[Sulaco]

I suppose the EGR is pretty much the only place to start, you're right on that one.

I did notice it appears easier to replace if you remove that firewall at the back of the engine. Otherwise it's impossible.

[horgantrevor]

change ERG

also on the m104 engine under the air pipe going across the top of engine their is a copper, brass . pipe sticking up an inch or so get some one to open and fit a pressure gauge to it and check fuel pressure

also at the end of that rail near the fan under the plastic black cover their is a second connection their is a inline filter in their they can get blocked remove and clean with a air line do not damage it very fine mesh

i would check throttle body also and clean easy job

the mot valve down on the right hand side of engine bay near abs pump it ticks like a fast heart beat make sure it is ticking

this valve is normally closed when car off and opens and closes when car is running remove pipe larger of the two back side put finger over you should have a vacuum put a large bolt in the block it and take car for spin and see if its faster i think it will be as the mot i think also may have had its day after 250,000 miles

keep us posted

[Sulaco]

http://www.peachparts.com/shopforum/showthread.php?p=1744307

That thread has a very helpful pictorial for identifying engine components. From what I can gather, US models don't have an MOT valve? I believe MOT is UK only?

[Sulaco]

Ugh, really wish I could chase this demon down. While driving my wife's 1994 E320 (also M104) on the interstate today, I had to hit the kick-down at 70mph for some busy lange changing. I really miss when my car accelerated like that. Nowadays I have to make sure there's no one for quite a while behind me before I change lanes, because full throttle in 3rd feels more like half throttle in fourth.

[C230KJaun]

Did you ever fix this issue on your car? I feel like I might be having the same problem. Thanks.