pe6opto
Hi I have a 1989 740 GL A/T (Sedan) with about 144000 on the clock. I bought it last fall when it had 137000 miles. When I bought it the O/D solenoid was bad, but in the first few days owning it, I pushed it to 105 down a local highway. Point being, it HAD at least a little more power than right now.

I noticed in the first few days that a few of my exhaust mani bolts were loose. I tightened them up and meant to replace the gasket but never have.

The transmission went just a few hundred miles and a few weeks after i bought the car. Totally my fault, this car obviously had sat for some time before it was brought to the car lot and then sold to me. The rear seal was most likely leaking, but I never took notice. I sourced a good running transmission from a 940 or a 960 and thats been running well for me ever since. The transmission has about 70000 less miles than the engine and frame do.


In the interim, I have replaced the plugs and wires, air filter, fuel filter battery,.

Anyway I am rambling at this point but the point im making is I have maintained this car but I have noticed recently especially a loss of power. I understand that this is a 3100lb car, with a 113 bhp motor, thats 21 years old yada yada yada but I know it shouldnt take 20-25 seconds to reach 65 mph! I can remember it being much faster and estimate it has done a sprint to 65 in under 12 seconds since I have owned it.

The car will only accelerate to highway speeds if I am careful to apply correct accelerator pressure to make it shift at the right times. If i do push too hard and it kicks down, sometimes i actually start going slower in the new higher gear!!
All that considered, when i get it up to a cruise at around 70 or so, it feels fine. At first. After a while that all changes.
The car has always been pretty slow, I know that and honestly its a good thing from a saftey and a me not getting tickets standpoint, but its lack of power becomes very evident on longer trips, and the symptoms become greater and harder to ignore.

When driving to and from cleveland and columbus, my car rides real nice at first and then all of a sudden it seems like its being choked and i notice i am on the middle of a long uphill. Bear in mind a long uphill in ohio is about a mile at best, which is no sweat for seemingly every car and most of the trucks on the road. I can feel the car slowly, oh so slowly being to lose speed as i travel down the road. If i give it more gas I downshift because of the kick-down and now Im in the situation I described earlier, a downshift that actually causes the rate of my deceleration to increase (I'm going slower, faster!). Anyway I reach the top of the hill going 55, 60 if im lucky and 50 if im not. I continue on my journey by gunning it downhill (reaching 70, 75 absolute tops) and slowing to 55 or less over the hills. This problem has been getting worse since i have owned the car. On my cleveland - columbus trips, this would only happen if i was driving very fast for extended periods and would go away if i eased off the gas for a bit. Now it happens about a quarter the way through the trip (about a half hour) with speeds of only approx 75. And even if i back off, it wont get better till the car cools.

So my question is, what can be causeing this. This car passed ohio e check emissions testing when I bought it. It does not have a CEL and never has. The temp gauge is always steady in the good range. I once had a radiator leak develop and I noticed this because I saw the gauge rising, but after patching the leak and refilling this has not been an issue either


My thoughts are, insufficient fuel/ fuel pressure. As I explained this loss of power is only really noticed on longer trips. My hypothesis is that extended periods of hard driving cause the fuel pump to work at 100% duty to attempt to keep the fuel pressure at appropriate levels. Hard highway driving will over time bring this pressure down. One thing that stands in the way of this is that if i stop the fuel system should quickly re-prime itself but this doesn't seem to be the case. perhaps it is something to do with the in tank pump?

bad seal at exhause mani and head causing leak and misrepresenting afr to downstream 02 sensors. I found this to be loose and tightened it. I retightened 2 of the bolts that became slightly loose over the winter and spring. I have put off replacing the gasket because I fear that some of the studs may break when removing the manifold nuts and dont want to deal with it. could a leak developed there be causing enough exhaust gas to leak past the gasket to seriously adversely affect performance.

bad or stretched throttle cable
My throttle cable might be worn because it seems like i can never give the car enough throttle to get it into what i would believe is its peak power range. Anything after about 3000 to at the absolute most 4000 rpms ( in first gear), will cause a kick down. I have tried loosening the kickdown cable to see if i can give it more throttle before kicking down, but it really seemed to make no positive difference.

clogged or partially blocked exhaust or cat
this car did pass e check, but in Ohio e check is sort of a joke, just a plug into the obd port looking for a cel, a check for a gas cap and a cat, so who knows. could my exhaust have collapsed baffles whose back-pressure causes this loss of power?

sludge?
I have been keeping up with oil changes, using synthetic. The oil does not seem especially dirty after some time but could it just be a dirty engine? I'm about to sea-foam this very soon if I don't think of anything soon.

should I maybe do a cylinder compression test on it? I have seen no signs of a bad head gasket but im really stumped.

What can i find my lost ponies!?!

Anyway thanks for all your help and time reading this. I hope it all made sense. Sorry it was a bit long but I wanted to explain everything I know because there are about a million things that I feel are relevant to this issue If there's anything else that is unclear just ask!

Alex

the day after posting that, I opened the hood and found the air intake hose between the throttle body and the MAF was kinked badly. There was also a hole in it too! Didnt I feel stupid right when i realized this. haha. I got myself a new hose in there and the car has run great ever since. I averaged 30 mpg on a long highway trip (700 miles) and the car has never felt stronger

It almost sounds like the cam timing has slipped a tooth. Do you know when the timing belt was last replaced?

Your car has an intank pump along with the one under the car. The intank pump could be bad causing loss of power most likely seen on acceleration. Make sure the new plug wires are ALWAYS Bougicord brand and the new plugs are plain-Jane cheapo copper plugs. Nothing fancy. Check the air filter and air filter box thermostat. Make sure it closes when the engine warms up. Constant heated air will eventually fry the MAS and produce bad fuel mixture signals.

stay away from the seafoam, that is not going to help you in this case IMO.
I'd stay away from the exhaust/cat also for now.
I'd start with compression as it seems you're onto that and its something good to know in any case, but mostly check fuel pressure, actual pressure with a guage, and see about the fuel filter. Your symptoms can be those of a filter meeting its limit, and running is stirring up deposits in it making flow more and more difficult as the trip wears on.

I got a new filter put in a few months back. They said the old one didnt look too bad either?

In a way it's almost seductive to think of all the things it 'could' be, but data rules. Again, check compression, check fuel pressure.