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Guest Message by DevFuse

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87 turbo running very rich (solved)

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11 replies to this topic

#1 Skip


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Posted 17 August 2003 - 06:09 PM

note: this is a continuation saga from the old EZ board
Vehicle: 87 turbo wagon 5 speed 4wd "James Bond button" on gear lever
Modifications: IC and boost pressure control valve, plus a few other go fast goodies
Problem: at about 7 psi of boost, engine goes extremely rich, stumbles and black smoke is evident out of exhaust pipe.
History: Problem came on all of a sudden, one day it was fine, next day problem. I made no modifications.
Power delivery is still fine at lower boost levels and car idles well.
(I have a boost gauge and air fuel ratio meter)
Boost appears to come on gradually as normal - no evidence of collapsed cat.
A/F goes to full rich as normal when intake manifold goes positive.
Engine is going into closed loop indicating coolant sensor is operating. A/F meter "tick tocks" as usual at normal cruise speeds.
No Check engine light.

Have tried
new MAF
new spark plugs
disabling hi energy ignition
changed timing through entire arc
removed By Pass Valve
tested and checked TPS operation against FSM
verified all vacuum/pressure connections
checked cap and rotor

Next stop?
Fuel pressure regulator? Why only at elevated boost levels?
ECU is out to lunch (never heard of this but first time for everything?)

Thanks for reading and any suggestions.
All comments will be addressed

#2 byb555


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Posted 17 August 2003 - 06:23 PM

My brother (Subaman) had a similar problem with his. Turned out to be the coolant thermo sensor. On the block just in front of the turbo. It was spewing enough fuel out the back to run a top fuel dragster when it was faulty. Changed it and problem solved.

May be the same thing.

#3 Skip


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Posted 17 August 2003 - 07:57 PM

Thanks for the reply, Brett
I have watched the A/F meter and it is definitely going into closed loop, I think this tells me the ECU is seeing the engine temp via the coolant sensor, but I will check it.
Thanks for the idea.

#4 gravelRX


    Driven with both feet.

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Posted 17 August 2003 - 10:09 PM

A small thread hijack

I've got the Autometer LED gauge and just wondering about what range does your gauge "tick tock" when sitting at a light after running for a while.

I take it during closed loop it's static?

Mine goes to the one red lean LED sporatically ( you can see the ECU compensate for it on the gauge) when idling and going down the mountain off throttle the light will actually go out on the lean side.

Guess knowing if we have the same gauge would be a good Q too.

Looking for a reference to see if mine is correct. Runs great, idles a bit rough though. Can listen to the idle change with the light fluctuation. Doesn't miss.

Curious and good luck with your quandary,


#5 Ozsubie


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Posted 17 August 2003 - 10:26 PM

Skip, I had a problem with over-rich mixtures on boost caused by the fuel return line going back to the tank getting blocked. Mine was slightly different in that as soon as the computer switched to open loop mode black smoke started pouring out the exhaust. This problem did happen very quickly though, one moment OK, the next smoke everywhere!! The FPR was initially the suspect component until I disconnected the return line in the engine bay and found it was pressurised. In my case the blockage was caused by the length of rubber hose connecting the return line to the tank. I had just replaced it a day ago with what the shop assured me was EFI hose. Turns out it wasn't EFI hose and the rubber all swelled up and it blocked itself:eek:

#6 Skip


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Posted 18 August 2003 - 08:32 AM

I would like to clarify some terms I used
open loop - this is when the engine is cold and the ECU is using pre-programed maps for fuel enrichment, it ignores the 02 sensor in this "mode" as it also is not up to op. temp. My meter sits static slightly lean at this time (02 sensor is not putting out due to this)

closed loop - this is the mode the ECU switches to after the FI coolant thermosensor tells it that the engine is approx. 140 deg F
The ECU now watches the 02 sensor output and switches the fuel delievery map from a rich condition to a lean condition, thus the "tick tock" seen on analog meters.

Jay, I have an analog (swing needle) type A/F meter.
It swings from a rich condition to a lean condition, the frequency of this metronome action varries with engine load and speed.

Pat. thanks I'll test it, no lift on this wagon, no changes in the fuel delivery sytem but worth a look.
Just seems to my feeble mind that if this were the case it would be rich at all speeds esp. lower power delivery as less fuel is needed. This is not the case, it is fine under 7 psi of boost.
One reason this may be the case is that after a certian MAF reading is reached (high air flow) and the engine RPM is high enough the ECU switches all fuel control over to the FPCR as the injectors are at their saturated state. (I have seen this on my 0-scope when I had it connected to the injector pulse output)
At this point if the fuel pressure where at an elevated point the car would go super rich, as is the case.

Thanks for the replies

#7 archemitis


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Posted 18 August 2003 - 10:23 AM

just turn the boost up till it runs stoic:headbang:

#8 Skip


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Posted 18 August 2003 - 02:26 PM

The ideal stoichiometric ratio is a very dangerous (read lean) condition to run in a turbo car when on boost.
The extra fuel is used to cool the combustion chamber temp and avoid the dreaded detonation.

#9 archemitis


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Posted 18 August 2003 - 03:25 PM

but if everything is in tune, and you are intercooled, the most hp is right at stoic. i'de rather run stoic than rich and melt my manifold and turbo

#10 Skip


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Posted 18 August 2003 - 06:42 PM

ARCHE Do what you want but you have it a bit backward.
an IC helps but does not bring down the combustion temps to a level below detonation. The extra fuel helps.
Your max HP without longevity is not what I want.

Now for an update
I have recently

watched warm up and it is transfering from open to closed loop, the FICS must be working.

checked the return line to the tank - open

got my CIS fuel pressure test gage out and rigged a fuel pressure tester - when the over rich condition happens I'm showing 45 psi. The FSM calls for 33.6 psi above intake manifold pressure (stumble occurs at ~ 8 psi) I deem it close enough.

I removed, cleaned and recharged my K&N using the factory recharge kit as per instructions.
This is a minor PITA as it is mounted under the the inner fender. Any one that thinks these don't work have never cleaned one!!
Result - no change exactly the same

Guys I love a challenge as much as the next guy but I'm running out of options.
Could the cat be partialy collapsed? It idles fine, thi holds a good vacuum at cruise and has power until the over rich condition happens.
My next check is maybe trying a different ECU.
Any other ideas?

#11 calebz


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Posted 18 August 2003 - 07:06 PM

Running stoichiometric raises combustion temps in comparison to running rich. thus giving you a much greater chance of melting your turbo and manifold. at the stoic ratio, one false move and you are in detonation mode.


If you can't figure it out, it must be one hell of a problem.

#12 Skip


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Posted 24 August 2003 - 10:42 AM

Connected my 0-scope to check spark voltage
Looked great??
Decided to rev it abit so grabbed the throttle cable and pulled.
She stumbled but then rev'd fine and the spark got better as it should with my ignition system.
Did it again as I felt a strange "wind" blowing on my hand??
No mechanical fan on her so where was the blowing coming from?
Did some searching and---
I have the IC connected to the factory intake plenum in such a way as to cause a forced fit - this done so it could not "blow apart", so I thought.
Well it had moved to a less than tight fit, therefore at low boost levels and off boost, it fit and sealed fine. Read no leak.
BUT when the boost pressure got high enough, the hose blew back a bit and allowed leakage. Lower the boost and the design pushed the hose back into a sealed position.
So much for over engineering?? I am designing a better solution for the intake plenum.
Well --
Same fuel squirt with less air yields a rich mix - bingo.

Thanks for all the help on this one, it did have me going for a bit.
Thanks especially to ______,as he had suggested this but at a different connection location.
As an aside, I like to look at the positive side of everything - a lot of things got cleaned and adjusted in pursuit of the solution.
She is running better than before the problem.
Still no CRX killer (I am a realist) but keeps up with traffic.
Boost on brothers but keep them hoses tight.

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