orcfromthesouth

I have my TD on Sunday and I noticed a limitation of power at about 5500 rpm. It feels like the engine was being braked very slightly and would not go over 5500. Definitivelly a significant power loss. Runs fine otherwise. No misfires or hesitation. Completelly normal in lower gears, 1-2 stoplight drag. Seems the power loss happens in high gears 4-6 and at speed.

Very recent ocurrence, as I took her to 168 mph last Sunday and the engine ran fine. No overheating or any other problem, except for a errant ABS sensor failing every so often.
Only event was changing to a new Shell 97 oct gas that claims to help efficiency.

Other theories: Gas filter, second distributor belt broken, MAF wire or oxigen sensor. Car has 40M miles.

At first i thought it was a clogged air filter (K&N). Cleaned it and loss remains.

Thanks

orcfromthesouth

I already did a search, and found similar questions , but not the same issue.

JasonAndreas

Have you checked the operation of the resonance flap? At 5500 RPM and with a throttle angle less than 60 degrees it should open.

BrokenE

I'll take a shot... I think it's either lack of fuel or lack of spark.

If it's lack of spark, then when you experience the problem, you might be able to immediately stop the car to tell if you smell unburned fuel. This is not exactly a definitive test, but it might be worth a shot. Lack of spark, or mis-fire, would normally give you a CEL though, so it's probably not likely you have an issue here.

For lack of fuel, however, there are some problems that will leave no evidence either physical or that the computer would catch. So my bet is with this one. Fuel filter could be partially clogged, fuel pump may be starting to go out, power to the fuel pump is not to consistent, lack of good ground to the pump, fuel tank ventalation and or fuel vapor return is not normal. Just a few guesses.

Saludos a todo Chile.

orcfromthesouth

Thanks.

How can I check the operation of the flap? I feel it works as the intake howl changes as usual. i haven't noticed any audible changes.

I have a new filter and haven't got around to change it. Fuel pump is new.

Is there any vacuum sensor that may not be working? Say a WOT vacuum sensor that adjusts high speed timing?

Saludos from Chile too!

Red rooster

With the flap not working you would notice a small loss from around 6000rpm onwards. The motor would still pull to the rev limit.
Power loss associated with big load is generally a fuel problem.
Does the motor go to 6800 in 2nd gear ?

Geoff

orcfromthesouth

Geoff,

Yes, the motor will pull strong to redline in 1-2 gears. I am zeroing on the fuel filter as the loss comes at, it seems, higher fuel feed/higher load situations. Given I used up my wrenching hours this week end on my sons Blazer, I will do the filter the next (or a few week evenings).

orcfromthesouth

Some more info. I have a recurring problem in that the ABS/ABD stops working and the warning lights come on. Cleaned all sensors. Thought it was a faulty sensor, but checking over a slippery surface found both fronts were locking. Searching the problem here gave a possible weak battery as the culprit.
Well. Checked the battery and it is weak, due for a change. Left it on the trickle charger overnight and will buy a new one monday.

orcfromthesouth

Amazing how cars have soul. Mine ran great almost the whole TD, and only did it start acting up at the end, when both the ABS/ABD went off, and the 5500 plus flat spot also appeared. I managed to shave off 0.5 sec on the autocross, and did a lap that puts me in 12th best. I love my car.

Tomorrow I will but the best battery I can get for it. Its earned it!

orcfromthesouth

Well. Changed the battery yesterday. Testdrive shows no power loss over 5500. Not sure, as it may be suggestion, but I feel the engine running sweeter than before.

ABS/ABD light has not come on either.

Will report progress.

VNTGSPD

Since electronics govern how most of the systems operate these days (and sometimes very low voltage), having a bad battery, alternator, and especially bad ground wires can wreak havoc on the whole cars systems.

Sounds like you may have found the issue. Good Luck!

orcfromthesouth

Yep. Wondering if anyone else has experienced this problem at the end of the battery's life?

Red rooster

I would be inclined to check the charging voltage . Your weak battery could be a dodgy alternator !
At 5000rpm the alternator is suppling the system volts. The battery is along for the ride .
Just a thought,

Geoff

orcfromthesouth

Red,

Agree. I was suspecting the alternator too. The battery was a old Volvo unit the PO had put in, probably at least 3 years ago. But I will check the charging anyways.

orcfromthesouth

Update on the 5500 power loss. First things first: fresh battery cured the ABD/ABS light and ABS loss.

Finally changed fuel filter today. Did a high speed run and loss remains. Help.
Will chech service manual to understand intake flap details. I know how and why they work. Its now my main suspect.