Rail Pressure on 2010 Cadillac SRX 3.0

Rick Technician New York Posted   Latest   Edited  
Delayed
Driveability
2010 Cadillac SRX 3.0L (Y LF1) 6-spd (6T70) — 3GYFNEEY3AS545010
Lt Fuel Trims
Rough Running Cold

Hello all, First time posting a question here. My main question is what the rail pressure should be, can't find a solid spec. . I'm getting 200 - 400 psi on the scan data which seems way low, but no code for sensor out of range or anything like that. 

The story is: the engine failed - rod through the block. We put in a used engine from same year and model vehicle. The tech ran it, drove the vehicle, signed off on it and the customer took it. Later the same day, she said it was running very rough, CEL was on. The tech said there were multiple misfire codes and lean codes for both banks. P0171, and P0174. 

The tech is no longer working here ( another story, unrelated ) so now I'm trying to figure out what's going on with this caddy. I've smoked it - nothing, vacuum is around 11-14in at idle which might be low but I'm not familiar with these vehicles since we're a Euro shop primarily. Low side fuel pressure is normal at around 50 - 60psi, ( gauge and scan data) I have a wps500x but if the scan data is lying and the pressure is actually in the thousands, I'm hesitant to even try that. 

Short term trims are normal all the time. long term fuel trims are +20's at partial throttle, but come down to more normal at idle. O2's all look completely normal. Vacuum gauge doesn't indicate plugged exhaust, and an in cylinder pattern doesn't show pressure in the exhaust either. There are exhaust leaks, but they're after the CATS. MAF is 3.5 - 5 gs/sec at idle and responds with no glitches. 

I've looked over all the connectors etc, and can't find anything crossed, unplugged or damaged. 

At this point I'm focusing on rail pressure. I drove it on the expy twice and it's not setting any pending or current codes, but it does run rough cold and the long term trims are definitely a problem. 

Perhaps someone has some insight on these vehicles, or can point me to something obvious that I'm overlooking. Thank you in advance.

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Josh Instructor
North Carolina
Josh
   

Dlid the replacement engine come complete? If so, can you swap throttle body with the original? These 3.0 engines had issues with the phantom fuel trim codes that were caused by the throttle body. There is no TSB or service info that will tell you this that I am aware of.

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Sherman Owner
Texas
Sherman
 

My experience is that about 500 or so pounds display on GDI engines at idle. The pressure rapidly goes way up when the throttle is depressed. 3000 PSI or so is what I've seen on average at about … RPM. I suspect carbon on valves, filthy injectors, etc; a maintenance item. Go to mode 6 and see if you show any sign of misfire counts, regardless of fuel trims or running. Mode 6 picks up on…

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Rick Technician
New York
Rick
 

The used engine did come complete, but unfortunately my parts guy sent it back to the salvage yard already. We called them and they've already buried it under a pile of other engines and can't be retrieved. I agree that it could be carbon or dirty injectors, Right before the other tech left, he had tried the top end cleaner. I got the car yesterday to start up and clear the county of mosquitos…

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Sherman Owner
Texas
Sherman
 

I have the Escan Elite…. and it is worth every dollar I paid for it. It allows fast, accurate diags for air, fuel, and correction! You should invest in one!

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Matt Technician
Texas
Matt
 

I'm sure you know but you can google a free VE calculator and plug your numbers in, not as nice as the eScan but gives you a basic idea.

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Matthew Owner/Technician
Oregon
Matthew
 

It's not hard to do a VE test without an Escan. I bought one just because I wanted to be lazy instead of doing a WOT and recording my numbers and punching them in a VE calculator, but it's just as accurate. Put your scanner on record and go do a quick drive and you'll have everything you need.

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Paul Mechanic
Illinois
Paul
 

You can use a regular scanner and select the appropriate pids to do ve test and/or pull up the load pid and record doing 1-2 shift. I like to include rear O2S also to verify that stay rich during test. Check fuel quality and achohol content just to be sure, however, won't effect pressures

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Robert Technician
Michigan
Robert
 

Just a quickie here 300/1300 sounds low without actually looking up a 2010 Caddy or any other info .. 550 @ Idle & above 2,000 psi Brake Torqued is about the quickest test for a failing pump and what you want to see . Lift pump remaining same with gauge bouncing is normal …Couple other things check the cam follower that drives the high psi pump and GM and 3 camshaft lobes also GM says its a…

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Juan Technician
California
Juan
 

The simplest & easiest thing on these cars is the purge valve. You can disconnect & plug the valve & recheck the truck.

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Caleb Diagnostician
Indiana
Caleb
   

So if you go WOT from a dead stop what does the rail pressure get too?? Do the 02s go full rich or full lean under WOT??

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Helpful
Geoff Diagnostician
Hawaii
Geoff
   

The "Fuel System" data list, in the ECM, should show Desired FRP and Actual FRP. They should mirror each other. e.g. on my 2008 Pontiac Solstice GXP, they read about 4 to 5 MPa idling, and then revving it in neutral, they both go to about 11 or 12 Mpa. (5 MPa is 725 PSI)

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Rick Technician
New York
Rick Delay
 

Thank you for all of the suggestions and information. sorry for the delay and lack of useful info for everyone on this. The customer decided to take the car and drive it. It’s not setting any codes, current or pending, I drove it over a weekend. I did try a HP pump, and the pressure increased to 400-500psi at idle and would get to … driving but the long term trims stayed high even after…

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