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Topic: OBD Confusion (Read 1911 times) |
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the_pot_noodle_kid
Newbie
ULT1M
 
Posts: 41
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OBD Confusion
« on: Nov 28th, 2004, 7:04pm » |
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Hello all. I hope someone can shed some light on my dilemma! Using OBD I have found the following on my 97 24 valve:
Bank 1 pre cat sensor sits at 0V - duff
Bank 1 post cat sensor jumps erratically between 0V and 1.275V - duff?
Bank 2 pre cat sensor switches between 0V (?) and 0.7V
Bank 2 post cat sensor switches between 0V and 1.275V - duff?
Short term FT 1 frequently increases to 32% in an effort to make O2S11 work
Long term FT 1 hovers around 0 (+/- 10%)
STFT2 hovers around 0 (+/- 4%)
LTFT2 hovers around 0 (+/- 3%)
Bank 1 sensor 1 has been replaced twice now, the latest one now seemingly dead. The car runs ok, but I am worried about #1 cat being flooded with fuel.
I have posted the scans on anyboard, reference 2711a. Any help or comments would be most welcome.
Cheers
Dave
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Eric_R
Administrator
Cosworth Owner 1998 - 2006 & site co-founder
Posts: 1792
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Re: OBD Confusion
« Reply #1 on: Nov 30th, 2004, 9:15pm » |
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Dave,
I've run through your scan and graphed it. It does indeed appear that the HO2S11 has failed - there are long periods of 0.00v and then it spikes to 1.25v, while the LTFT1 climbs to the max to shock it into operation.
The LTFT appear to working okay and it doesn't appear to be a fuelling fault - sometimes if the fuelling is incorrect the HO2S sensor will not 'switch' because the fuel/air mixture doesn't change. On the plus side the HO2S12 sensor is working satisfactorily, which tends to rule out a general loom problem.
Leaving aside the after-cat sensors for a moment, (they are not used for fuelling) it worries me that you have changed the sencor before and a new one had gone faulty - these sensors should work for years without problems. When you installed the new one did you check the wiring very carefully for chafing and the connection for security. The signal voltages are very small and they are susceptable to wiring and connector condition.
On the other hand perhaps the new sensor was faulty. I can only suggest you check the all the wiring to the sensor carefully before replacing it again, and while you're at it the HO2S22 as well. Then clean the MAF with residue-free cleaner.
When that's done run a new scan selecting
RPM (it's always best to know when the engine is at idle to check the fuel trims)
HO2S 11,12,21,22
LTFT1, 2
Make sure the engine is properly hot and then let it idle as part of the scan.
Could you also go to the CODES page and download any DTCs the car is showing.
HTH
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After a Cosworth, anything else is just ... ordinary
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the_pot_noodle_kid
Newbie
ULT1M
Posts: 41
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Re: OBD Confusion
« Reply #2 on: Dec 1st, 2004, 5:15pm » |
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Thanks for the reply Eric. I wondered if it was an earth problem, I've cleaned the earth strap connections, but don't know if there's any other earthing point that is relevant. I will do as you say and get the trouble codes.
Thanks again
Dave
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