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3 inch exhaust, dies off throttle?

D

DavePolyakov

Member
Joined
Aug 3, 2020
Location
Shoreline, WA
1990 740 Turbo with 15g + 3-inch downpipe and high flow catalytic converter. I will weld on the muffler when I have the time.

Since I've installed the exhaust the car will shut off when I let off the throttle and shift to neutral when in boost. It dies gently, as it would if you shut off the car normally. Rpm's drop to 800 then it shuts off.

At one point I had larger injectors and 012 AMM installed and I thought that was the issue. After going back to stock injectors and AMM the issue has persisted with no change. I've tried multiple different AMM's and no change. The only thing I've changed was the exhaust.

Anyone else experienced similar symptoms after installing 3-inch DP and exhaust?
 
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Where is your O2 sensor in the exhaust? Makes a difference. 3” exhaust won’t make it stall. Everything in exhaust is aft of what does that. Have a good look at false air leaks and all basics that will make a car with an air mass meter stall.
 
Are you sure the idle switch is working correctly? Another thought is the throttle plate closed all the way? It should be adjusted slightly open.
 
I'm going to readjust the idle and see how it runs. I'm pretty sure it's idling low. That would make sense right?

I've done a battery disconnect and the o2 sensor is new and in the stock location.
 
The sensor is new, but is it the correct Bosch one?
If some other aftermarket brand: Just ditch it.
BR
 
Maybe base idle is too low. Set to 500 rpm with halfway warmed up engine. Set it via the throttle stop screw and pinch the IAC hose closed. Then adjust TPS again. Solved the stalling of my 240 when coming of boost.
 
Yep, the throttle linkage rod just needed a very fine adjustment, now the problem is gone! I found it easiest to adjust by leaving the car running and adjusting while it's on. It needed to be very exact or the car would keep stalling. I basically did trial and error.
 
Adjusting the idle didn't actually solve the issue, it still occasionally dies and it is not boosting properly at all. I decided to check fuse #11 for the in-take pump and found out that it wasn't even there:omg:
I put a fuse in and went for a drive assuming that this was the issue but there was no difference. Does this mean I should look into replacing the in-take pump? The main pump is pretty loud and I've read that this can be a symptom of the in-take pump not working.
 
The o2 sensor is in the same location as stock just flipped 180 degrees so it's on top of the downpipe but the same distance from the turbo. I thought this was fine to do? Here's a video of the issue that occurs in boost. It gets much worse at a higher boost, with lots of bucking and such.

https://youtu.be/D8lh794DNqs
 
You may have a big air leak somewhere you missed. I would perform a smoke test.

The oxygen sensor has nothing to do with breaking up at high boost. The ECM isn't "listening" to the sensor once you are in open loop. On the throttle and in boost= open loop.
 
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