Latest update. Mechanic has had my car for 2 days.....went to see him today and he says its probably the fuel pump. He's having another person check it out tomorrow. Anything I should know or questions that should be asked. Setting my pride/ego aside, I know nothing about cars

 

Just be aware that the STR has a unique fuel system that is not shared by any other S Type! It has two pumps that feed the engine directly with both of them running full out from about 3000 rpm and up.

Each pump is about $900-$1100! So test them good as they are not a known problem but several have been replaced. You also have fuel rail pressure sensor which can fail but will give a code.

Do you have any codes?
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There are also 2 fuel pump modules on the STR (and only on it). Proper dealer diagnostic tool can help here

 

Spoke w/ my mechanic & his other specialist believes its the fuel pump(s) BUT my mechanic doesnt think thats the problem. He said the fuel pressure is fine. The MAF sensor is fine & the only thing i can think of (thanks to Google) is a vacuum leak. I dont know what else to do
Here's the codes P0171 and P0174

 

True enough those may but need not be due to an air leak. Most likely the air filter, its box or the trunking from the box to the engine. Next step is to check LTFTs (see my sig below) at idle and about 2500rpm - post them by all means - using any OBD tool with what they call "live data", such as an elm327 (about $10). If it's an air leak you'll have LTFTs well off zero at idle which flatten out as you rev.

 

hmmmmm mechanic did change the air filter with the initial problem

 

Well if you think it's an air leak lets dig a little more.

The plastic intake tubes can get holes especially the corrugated portion where the hole can hide in a wrinkle.

The air box lid is a SOB to latch properly. I remove the entire plastic intake system air box and all when I change the air filter. It's pretty easy and then you can clean the dirt out of air box too.

There have been several people get bit when they have a vacuum leak from the power brake booster lines. They are not easy to check and as time goes by there are rubber seals on the hoses that can deteriorate. I would use an unlit propane torch and/or spray carb cleaner around all the possible leak areas. Listen for an RPM change.
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And he may not have closed the box properly, or the intake hose cracked during the procedure. Check all of it carefully. Everything between the airbox and the throttle body.

Oh ... see the post directly above by tbird6.

 

Just a quick update..
Mechanic changed the power brake booster lines but the car is still running lean (even at idle)
I gave him a list of everything mentioned above & still dont have a resolution, FML

 

Still sounds like an air leak.
Have you had time to check the fuel trims as JagV8 suggested?

Still not sure if the air box and lid have been completely removed? I like to latch the air box off the car and install the whole thing as an assembly. It really is a tight fit and most mechanics won't take the time to remove the intake tract.

After clearing the codes are you only getting the 171 and 174 codes coming back? No other codes? The EGR codes stopped repeating?
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Are you in Oakland California? If so and your car can make it or tow it bring it to Sacramento to Stewarts Auto. If you've read my post before you will see that after some initial misunderstanding on my part I think they are a great shop. Give them a call and talk to Matt. Tell him Diamond recommended you call.

Stewart's Automotive Specialists of Sacramento

 

Oh yeah I forgot to add that I had the same codes when I first got my car a while back and it ended up being the airbox it wasn't put back together correctly by the dealers mechanic.

 

The results came back from the new mechanic after they replaced the MAF Sensor
sorry to say we started your car this morning and the engine light was back on with the same codes, we checked again for air leaks and we found a leak behind the supercharger, it could be the back plate or even the EGR valve. Having done a few of these I appreciate how hard it is to get back there and put all this back together, they really are a nightmare...
I suspect it is something that's not gone back in correctly, the end plate on the supercharger is also the air intake, it has a big rubber seal around it which is attached to an aluminum plate, it's extremely hard to get back into place, we've spent a couple of hours on one in the past getting it right, and that's just getting the gasket, bolt holes etc. lined up.

Hopefully thats the fix!!!!

 

Well that's a new one!!

I have never heard of the back plate on the super charger leaking. Since most of the time the super charger should be making pressure? Do you have any stains from this leakage?


Here is a picture of the super charger with the back plate removed.




Did he remove the back plate on the SC when he changed your coolant hose? It does not need to be removed. Did he get the vacuum hoses on properly?? If the EGR is leaking there should be specific EGR codes not these general air leak codes.

Something is not adding up? Not sure what it is?
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Took the car back to my original mechanic...be was certain it wasnt the back plane, but it did lead him to a vacuum hose (didnt advise of the location) that needed to be replaced (think it was the clamp). he fixed that and all was good....until!
Yesterday was driving on the freeway, check engine light w/o a warning of Restricted Performance, which i was a little happy about.
Checked the code, P0400
Mechanic told me that its the EGR Valve that most likely needs to be cleaned
Need to get my car smogged, so i guess I have to do this myself

 

It's a shame that the EGR valve and tube was not changed when you had the super charger off. It's getting common to find EGR problems and holes in the Exhaust tube. Just miles of driving as this was not reported until the cars have been on the road for a few years.

Looks like the SC will need to come back off? All those gaskets too.
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