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Discussion Starter #1
Today, I just installed a new downpipe (catless) from SJS on my 93.5 Esprit. It also replaced the exhaust backpressure valve. The install was very straightforward, but on my way home, I noticed that my boost was low. the stock gauge never went past 0.4 Bar of manifold pressure. Also, about half way home, my check engine light turned on. I checked with the diagnostic plug and it revealed a code 23 (low mass air temperature.) Currently, I can't get my laptop to connected to the ECM (usb-serial adapter issue i think).

Would a code 23 limit boost pressure? Also, has anyone had a code 23 before? COuld it be totally random that my MAT sensor took a dump? seems unlikely.

any help would be appreciated
 

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I decatted my 88 by building my own replacement pipe and I had no issues at all except for a slight backfire on decelleration, however the 88 is the last year of the Bosch CIS system, you have the GM FI, but I still have a O2 sensor and it caused no issues at all with the driveability. Are you certain you didnt disturb any vacuum lines at all.
 

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Discussion Starter #3
I am not seeing where the MAT sensor issue is coming from, at all.

I'll take it for a drive tomorrow and see if the boost issue is still there.
 

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My car (1994 S4) also has the "track pipe" (straight pipe in place of cat--from JAE) and my car also has the short EBP valve replacement pipe (also from JAE). Never any problems at all. Did you remember to tie off the EBP vacuum line???
 

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I installed the SJ downpipe in my 89 SE a couple years ago. The pipe replaced the cat and the EBPV valve.
I used my existing O2 sensor, plugged the vacuum lines on the EBPV solenoid, and the throttle jacking solenoid which I also disconnected from the throttle.
Car sounds awesome. Engine felt stronger, but runs slightly rich with a bit of off throttle exhaust pops. It is a bit louder. I had also done the "ram air conversion" at the same time. The only negative is that it stinks a bit. I am considering a "high flow" cat for that reason. BTW the previous owner had installed a Magnaflow dual outlet exhaust.
I had no other issues, and in fact my car ran at least as strong as before.
So if you did all the steps correctly, then you either disturbed something or have a new issue
 

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Discussion Starter #6
Thanks for the replies. Seems out of place why I have these new issues. I guess I'll get them sorted out. Btw, is there a way to clear trouble codes without using freescan?
 

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It would certainly be a big coincidence for the sensor to go bad at the same time as the cat pipe install so it's more than likely there's a loose wire/bad connection somewhere.

Check the connections for the MAT sensor, ECU coolant temp sensor and MAP sensor and also the wastegate and EBPV solenoid connections and pressure lines.

Should be something simple in the area you were working.
 

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Discussion Starter #8
I think I know why the MAT sensor is triggering the CEL. 2 days ago, I checking vacuum lines, and I removed the charge cooler. I then started the car to listen for any vacuum leaks. likely, the code was triggered when I started the car with the mat unplugged, but it didn't set the light off until yesterday when I was driving the car. I just need to reset the CEL to see if that is all that is going on. Once I get that out of the way, then I'll move onto the boost issue.
 

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Discussion Starter #9
update:

I found my old laptop (10 years old) docking station that has a serial port on it. I was finally able to get freescan working from the engine compartment ALDL connection. (the passenger footwell ALDL doesn't seem to connect.)

The code 23 I was getting from counting the CEL wasn't there. What was there is a code 26 (quad driver circuit.) one item listed as part of the QDM is wastegate control. hmm.......off to figure this out.
 

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Discussion Starter #12
replaced the fuse. cleared the codes, and went for a test drive.

so far so good! I wonder why the fuse blew though......
 

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I remember something about having to cap off a waste gate vacuum when I did mine.
No, don't cap the waste gate pressure line but cap the vacuum line that went to the EBPV that was eliminated.

If you cap the waste gate line, you'd be limited to the mechanical setting of the spring which should be .65 bar.
 

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Discussion Starter #14
No, don't cap the waste gate pressure line but cap the vacuum line that went to the EBPV that was eliminated.

If you cap the waste gate line, you'd be limited to the mechanical setting of the spring which should be .65 bar.
that wouldn't be a good plan. ha :no:
 
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