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Topic: MAF - help needed! (Read 1625 times) |
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OHC
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MAF - help needed!
« on: May 3rd, 2005, 11:35am » |
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Hallo!
I' d like to check the MAF and HO2S output, but I have no OBD lead. I know that it's possible to read the signal by multimeter but I don't know what contacts I should apply multimeter's probes to! Yes, I saw 'troubleshooting' section in HO2S and MAF data page. I'm not a car electrician so it helps but not so much!
Please, that pins of MAF plug should I apply positive and negative multimeter's probe to measure return signal!
Please, also explain the same about HO2S11!
It will help me so much!
Best regards and thanks in adv.
OHC
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Eric_R
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Cosworth Owner 1998 - 2006 & site co-founder
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Re: MAF - help needed!
« Reply #1 on: May 3rd, 2005, 7:08pm » |
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OHC
I take it you have the 16V engine?
In the case of the MAF, leave the multiplug in place and read the voltage across the white/blue and brown/blue wires, pins 1 and 2. (You can do this by using thin wires trailing out from the plug - but don't let them short or touch ground). With the aircon off and the gearbox in neutral (if Auto) you are looking for a voltage of 0.234 at idle. This value should change consistently at higher revs.
With the HO2S sensors there are four wires. One pair are supply and ground for the heater - the other two should show a voltage switching between 0.1V and 0.8V or thereabouts. The wires you need are white and brown.
If 'switching' between the lower and higher voltage does not take place it doesn't automatically mean that the sensor is faulty - there are other causes too.
HTH
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OHC
Junior Member
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Re: MAF - help needed!
« Reply #2 on: May 4th, 2005, 5:47am » |
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Thanks, Eric!
I tried measuring HO2S signal as you say! The voltage gradually rises: 0,02V..0,1V..etc. up to 0,93V and then drops: 0,93V..0,63V..etc. till 0,02V and then rises again! Is it 'switching' as it should be or HO2S should only literally switch from 0,1V to 0,8V and show no other voltage! Please, help, low MPG will ruin me!
Best regs,
OHC
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Eric_R
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Re: MAF - help needed!
« Reply #3 on: May 4th, 2005, 9:27pm » |
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OHC,
Yes, the voltage can show voltages in between 0.1 and 0.8. There should be a regular switching from the high voltage to the low votage every 0.6 of a second. If you have a DMM it might be slow to register a change - some analogue voltmeters might be better at showing the change. The actual voltage (as long as its not zero or a negative) is not as important as the actual switch itself.
If there is not a negative voltage, or a 0.0 v reading the HO2S would probably be okay.
How did you get on with the MAF?
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OHC
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Re: MAF - help needed!
« Reply #4 on: May 5th, 2005, 6:38am » |
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Thanks, Eric!
I,ve measured MAF voltage at idle! It says 0,68 -0,69 V at idle! And I'm slightly confused: in TROUBLESHOOTING section MAF signal should be 0,6V and you say 0,234V! Where is the true? All the same my volts are not correct and I have to replace MAF- all the simptoms are here: low MPG, greatly increasing when at idle, sooty exhaust pipe, loss of power at full throttle! I've tried to clean MAF but to no avail! 
But what if idle RPM are sligtly more due to faulty TPS! The volume of air increases so does the MAF voltage! Can i disconnect TPS at idle to eliminate its influence?  IACV is new and OK!
Best regards,
OHC
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Eric_R
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Re: MAF - help needed!
« Reply #5 on: May 7th, 2005, 12:16pm » |
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OHC,
The MAFV reading of 0.234 shown on the Troubleshooting page was not at Idle - the load of the engine is 75% - this is intended as a guide only. I'll have to make that more clear.
If you read further you'll see that the MAFV should not be greater than 1V at idle, with the autobox in N and the aircon off. My own reading with the gear in P and the aircon on is 0.789 V at 741 RPM.
The trouble here is that without an OBD lead we can't see the values of the other sensors, or the fuel trims or whether the fuelling is in Open or Closed Loop.
On the basis of that voltage reading it appears that the MAF is not to blame. We need a proper reading using all of OBD in order to determine the cause. It may well be that the engine is in Open Loop, or that the fuel pressure regulator is too high, or that one of the ECT or IAT sensors is faulty - without the OBD lead we're not going to get any further.
Is there anyone you can meet in your area with an OBD lead?
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OHC
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Re: MAF - help needed!
« Reply #6 on: May 7th, 2005, 3:21pm » |
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Thanks, Eric!
The problems is here in Russia even FMD doesn't know much about OBD! If they see no DTC - they consider everything OK! I tried to explain them they what to do with their expensive WDS but to no avail! They obliged me to replace IACV saying it's faulty if engine doesn't stall if IACV disconnected at idle!  Now from your brilliant site I know that it won't!
Meanwhile I've found the garage specializing on Fords (particularly frog-eyed Scorps). In phone talks the owner said that he usually checks all the sensors' values, RTFT and STFT! So I hope it's a right person! Moreover, he has spare parts available from brakers so I needn't look for anything!
Meanwhile I cleaned MAF and choke butterfly unit with better carb cleaner! Slight improve in performance! And next weekend I'm going to OBD check!
Wish me good luck and many thanks to you and your sight!
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