Car slow during WOT

[Spetz]

Hi everyone,

My 2003 Mitsubishi Diamante with 150,000 miles on it seems like it accelerates slower at WOT than at moderate throttle positions.

At WOT it seems to make more noise yet accelerate slower and feels almost like something is suffocating/restricting it.

What could this be?

 

[Chris142]

Fuel pressure? Filter?

 

[Spetz]

Fuel filter was recently replaced.

Unsure about fuel pressure though

 

[WobblyElvis]

clogged CAT?

 

[Spetz]

How would I check that?
It is the original one currently.
I have been doing some reading on symptoms and I do sometimes get rpm dependent rattling which I thought was the exhaust

 

[Danno]

I suspect the cat as well, they tend to overheat if plugged. A shop checks upstream vs downstream pressures to determine if it is plugged

 

[das_peikko]

Unscrew the upstream oxygen sensor and install an exhaust backpressure gauge. 2 PSI max.

 

[Dylan1303]

My cruze is faster at 80% throttle than wot. My cruze goes into open loop at wot. Maybe yours does too?

 

[eljefino]

Originally Posted By: WobblyElvis
clogged CAT?


x2

 

[NHGUY]

TPS bad at the upper end?

 

[dlundblad]

Unscrew and remove all 02 sensors from the cat.

 

[zrxkawboy]

another vote for a clogged cat

 

[another Todd]

Another clogged cat vote here.

 

[Spetz]

Why would a car be slower on WOT compared to part throttle if there is a clogged cat?

The car would burn a fair bit of oil (1 quarter per thousand miles) due to valve stem seals - Could this clog a cat?
The valve stem seals have since been replaced and there is no visible oil usage.

Also... silly question, but can I remove the cat and clean it out with something like brake cleaner?

 

[SteveSRT8]

clogged cat can be difficult to figure out but is easy to eliminate.

Pull the forward O2 sensor and take her for a spin.

 

[Trav]

Originally Posted By: Spetz
Why would a car be slower on WOT compared to part throttle if there is a clogged cat?

The car would burn a fair bit of oil (1 quarter per thousand miles) due to valve stem seals - Could this clog a cat?
The valve stem seals have since been replaced and there is no visible oil usage.

Also... silly question, but can I remove the cat and clean it out with something like brake cleaner?


Back pressure. Sure you can take it off and knock the insides out then run an anti fouler on the rear O2 if you have no emission inspection.

 

[Silverado12]

Apparently This Works. LINK

 

[punisher]

First step, pull codes. Look for lean and or catalyst efficiency codes. Verify you aren't going lean at WOT. Use scan tool first, monitor fuel trims on accel, and WOT. Many control systems go open loop at WOT so there is a possibility you might not have trim displays. After that verify fuel pressure, MAP/MAF voltage, then ck for clogged cats. SOP for "lack of accel" concern.

Oh, if it has a distributor, check timing. Got bit a couple of times by not checking that.

 

[Spetz]

Thanks everyone.

The car is a 2003 and only has 1 o2 sensor (before the cat) and I don't believe is intelligent enough to throw any codes etc.

Could a clogged cat cause rough idle issues at all?

I will try pulling the cat off and looking inside it to see if it looks bad in any way and if it does I will replace it