Background

Most others have simply not cared to pursue the delete because 96+ ECUs are not terribly expensive on eBay. However, I have just recently purchased an IPD tuned '95 ECU from a guy on Facebook because it was such a great deal so simply buying a cheap stock ECU was not an option for me, I wanted to keep my IPD tuned ECU. Also, the reason I wanted to delete my EGR was not because the system was malfunctioning and throwing CELs or because of a stuck open valve. I pursued this because during a boost leak test, I found a large leak around the diaphragm of the EGR valve. I would assume the stem seals around the shaft that connects the diaphragm and the valve have gone bad and are letting air leak through the diaphragm. At full boost even though the EGR valve is closed, a boost leak is created because of this. Believe it or not, this was the only major leak I found during my boost leak test and I am underboosting about 4 psi so it's making a huge difference. Yes, I already thoroughly cleaner out the EGR valve during a PCV job 1 year ago. My issue is not a stuck open valve which would also cause a significant boost leak and I think is a more common problem.

I am now wondering if the use of carb cleaner (which others have used to clean the EGR) could have destroyed the stem seals which I assume are some type of rubber. There is really nothing I can do to repair it and I have already been looking for a replacement, but in the mean time I figured I would try the delete. If I could successfully keep the CELs away, I could install a block off plate between the EGR valve and intake manifold and block all flow but more importantly, block my boost leak.

Previous work

So it's labeled 2.0 because if you google Volvo 850 EGR delete you come across a pretty infamous thread back from 2009 where a guy fooled his EGR temp sensor with a 1k ohm 1/4W resistor. It held his CEL at bay for maybe two days before ultimately returning.

https://volvoforums.com/forum/volvo-...success-27022/


My research

So I started in the same area as my predecessor. I disconnected the temp sensor and hooked up a multimeter to read the ohms the temp gauge reads since it is an RTD sensor and measures via resistance. Predecessor guy mentions that he was reading 4.5 ohms. I think maybe he missed the little K in the top corner of his multimeter because I measured nowhere near that. So even before I started the car, I read out 300k ohms because the sensor was at ambient temp (about 50F that night). As soon as I drove in EGR conditions, that number began to drop rather rapidly. In EGR conditions, I read anywhere from 0.5k to 10k ohms which makes sense why predecessors 1k ohm resistor worked for a while and not his 10 ohm. So upon further investigation, I found that when cruising on the highway at 65 mph, the temp sensor would read around 4k ohms when coasting down a slight slope and it would only go down to 0.5k ohms if I was cruising up a steep incline. I guess this makes sense because although the engine speed (in RPM) is the same, there is alot more load uphill and hotter exhaust gases. So you would expect the resistance number to fluctuate like that even at constant wheel and engine speed.

So I tried to figure out why my predecessors 1k ohm resistor did not work. I figure it's because dropping below 1k ohms on the RTD sensor was rare. Like I mentioned, it would only happen when chugging uphill and as soon as the ground leveled out, it would jump back up to the 3k-5k range. My guess is that the ECU interprets the low reading as an error because unless you are on a really odd road with a constant uphill slope for miles and miles, reading a constant 1k ohm is unusual. If the RTD sensor was super accurate, the ECU could predict exactly what resistance should be measured based off of engine load and expected exhaust gas flow. I noticed from field testing, the RTD fluctuates like crazy so my assumption is that the ECU has a certain range it is happy with and 1k ohm may have been to low for a prolonged period.

Because assorted resistor packs are super cheap on eBay I decided to just buy a huge variety and start my testing. They are all 1/4W resistors but that should not matter because the wattage rating only tells you what they can withstand until they burn up, 1/2W resistors would work fine too. Since 0.5k ohm was the bottom of my range I measured and during highway crusining 3k-5k was "normal", I decided to start with a 2.2k ohm resistor and work my way incrementally until I got to 10k ohms. If none worked, I would conclude that a fixed ohm resistor cannot be used to trick the ECU. I was fearing this may be the case.


My results

Of course I am jumping the gun because I am excited I may have conquered what no one has conquered in the past (according to hours of google searching) .I have been driving 4 days to and from work (about 30 miles round trip) and no CEL has returned. To make sure I wouldn't have engine running issues when I eventually block off the EGR, I disconnected the vacuum signal from the EGR controller so the valve has also not been opening the last 4 days. I confirmed this by driving with my multimeter hooked up to the temp sensor and when I hit EGR conditions, the temp sensor doesn't fluctuate at all meaning no exhaust gas is being recirculated. Absolutely no stumbling issues with the motor.

I will update as time goes on and each time I ahve to switch resistors if the 2.2k ohm fails