850 MAF and TPS

Post by **Jack Rock** » 17 Jun 2010, 10:05

I've been having trouble passing my emissions test and with many parts and $ later it still won't pass. New part; plugs, wires, cap, rotor, flex pipe, catalytic converter and O2 sensor. My local shop (dealer is 1hr away) is not able to fully diagnose the problem with their equipment. He said that the car keep going back into open loop when opening the throttle. He suspects the MAF or TPS but is unable to test them. He said he was able to verify that the temp sensor is functioning good. The O2 sensor was the first part changed based on code 0136 (if memory serves me right). He said that the voltage from the O2 sensor is ranging from .8 to 1.2 which it isn't even supposed to do (max .8 I guess). This afternoon he's going to put the old O2 sensor back in (I did this job at home and kept the old parts - maybe it was ok) to see if he gets this right voltages. There are no codes. My question is how does one test the MAF and TPS without Volvo diagnostic equipment? Any help would be great!

Post by **dcarlson12** » 17 Jun 2010, 13:55

Edit: Sorry I missed in your 'profile' your vehicle is a 97 850 Turbo
I have now uploaded the Input Signals file which describes output signal values for both the MAF and Throttle Position Sensor after putting your vehicle description into VADIS.
Have left the other file also. Perhaps it is the same, not sure....
I have attached a .pdf file from VADIS. For a vehicle spec I just put in 1995 850.
If you can give more info then perhaps we could provide more help. i.e. if it has any DTC's or ???

Post by **Jack Rock** » 17 Jun 2010, 14:24

Sorry about the lack of info, I'm new here and I thought the vehicle info I entered when signing up was automatically attached at the bottom of the post. It's a 1997 850 T5 and there are no DTC's. That's a great file, I'm assuming my model is slightly different but fundamentally the same.

850tech · Post by **850tech** » 17 Jun 2010, 15:44

Can you post your drive clean test readings, both ASM 25/25 and curb idle.
Also is this test for sticker renewal or ownership transfer and is the shop doing the work drive clean repair licenced or inspection only?

Post by **Jack Rock** » 17 Jun 2010, 17:44

I'll have to post the results tomorrow, I'm at work. This is an ownership transfer so I don't qualify for a conditional pass and yes, they are licenced for repair.

Post by **Jack Rock** » 18 Jun 2010, 14:43

Thanks for the 97 info. Here's the readings, after this first one is the new O2 sensor, after the second is the new ignition parts (it got worse again but I also used a can of "guaranteed to pass" which my mechanic said was a bad idea), after the last test shown in the picture is when they put in the new cat but I don't have that test - it's in the car.

Just got back from the shop, compression test shows cylinder four low, it improves when putting a small amount of oil on top. I guess this means I likely have a cracked ring allowing oil to get to the combustion chamber, burning and causing high HC readings. Any ideas of what the cost of an engine job would be?

850tech · Post by **850tech** » 19 Jun 2010, 15:10

Well compression could cause high readings across the board. A lean missfire caused by a vacuum leak or poor fuel pressure could cause these readings as wel as carbon build up on the valves and pistons or a failed a cat, but you've replaced that. Do you know how low #4 compression was? Also does the car run perfect? no stumbles, rough idle, etc?

Post by **Jack Rock** » 20 Jun 2010, 12:37

The car runs great as far as I'm concerned, no stumbles, idle is 95% smooth, idles at about 1000rpm. Here are the compression test results; 1: 142/165, 2: 143/167, 3: 138/166, 4: 125/155, 5: 136/165 (dry/wet). I'm no expert by any means but although four is lower and probably getting a little tired, I'm not convinced that it's a concern considering all cylinders have a 25-30 pound difference between wet and dry. That leads me to think that all cylinder rings are performing the same. Maybe carbon build up on cylinder four's valves is allowing this pressure leak or drop. The strange thing is that the mechanic said it's cycling into open loop as it sits on the diagnostic machine, I'm not sure at what interval (I'll call on Monday to find this out). He also said that at this time it gives a puff of blue smoke, then goes away as it enter closed loop again. I'm going to double check my vacuum lines, especially the elbows I've recently read about.

ronnieleetwist · Post by **ronnieleetwist** » 20 Jun 2010, 16:00

To test the MAF, with the car running, tap the MAf housing sharply (don't need to WHACK it) with a screwdriver handle. If the engine stumbles, you have a MAF problem. The other I can't help you with. Good luck

Post by **Jack Rock** » 20 Jun 2010, 19:14

MAF seems to be working, no change when tapping, mechanic tested it and said the return voltages were according to spec. When checking my vacuum lines I did notice a deteriorated fuel line under the intake manifold cover. It's the 3 or 4 inch long rubber line with the vacuum attached, not sure if it's return or send. I'll replace it tomorrow, likely not my issue though. Anybody have any input on my compression results?