Fuel Trims/codes- 4.2l 2000
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Junior User
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Ok, here is another part of my dilemma. This engine is running pretty rough and the fuel trim numbers never really stay in one place. This makes it very hard to check for vacuum leaks by spraying because it is hard to tell if the numbers are changing because of me spraying or just because of the way it is running. I know that if I spray right down the intake the engine bogs down a lot, but so far none of my spraying has made that happen around the intake or elsewhere.
Any thoughts? Ive ordered itake manifold gaskets, but I am just worried that they won't fix it... ARGH!
Any thoughts? Ive ordered itake manifold gaskets, but I am just worried that they won't fix it... ARGH!
Elder User
Joined: Jan 2008
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You have to decide what strategy you're going to takel. Are you going fix the misfire DTC or the lean DTC? Make up your mind instead of jumping all over the place. If you spray in a COMMON area both Bank 1 and Bank 2 are going to change, not just Bank 1. If you spray in an area that is not common then Bank 1 could change by itself without effecting Bank 2. You say you have three sensors that are 25% to 32% which then drop to -25%. That's a huge change to happen instantaneously. The STFTs might change that quickly, but not your LTFTs. You didn't give a POS or NEG designator for your 25-32% value. Are they POS or NEG? Are you saying they switched all the way from +25% to +32% to -25%. You do see what a big jump that is don't you? I have a hard time believing you have 3 sensors that are ALL reading the same value of +25% to +32%. One would have to be an S2 be it on Bank 1 or Bank 2. When you spray directly down the intake you sent the whole system RICH. Doing that isn't going to find your problem. Go to your first DTC and work on that one then move to the next if there is still a problem after you fix the first one.
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OK, sorry if I made this unclear.
3 out of 4 read 25-32 + fairly consistently. The STFT B1 is the one that varies from -32 up to +5. The problem is that sometimes it goes way up to +32 and then the B1 LTFT drops to 0.
My main concern with diagnosing is that all of the sensors seem to fluctuate 5 or more points regardless of me spraying or not. So it seems hard to tell if the change in fuel trim is caused by me or by the engine.
The reason I sprayed down the intake was to see how the carb cleaner affected my readings. I figured if I could observe the differences when I knew it would be affecting the readings then I would know what I was looking for when I sprayed around the intake. But again, my problem is that the readings never seem to stay in one place.
3 out of 4 read 25-32 + fairly consistently. The STFT B1 is the one that varies from -32 up to +5. The problem is that sometimes it goes way up to +32 and then the B1 LTFT drops to 0.
My main concern with diagnosing is that all of the sensors seem to fluctuate 5 or more points regardless of me spraying or not. So it seems hard to tell if the change in fuel trim is caused by me or by the engine.
The reason I sprayed down the intake was to see how the carb cleaner affected my readings. I figured if I could observe the differences when I knew it would be affecting the readings then I would know what I was looking for when I sprayed around the intake. But again, my problem is that the readings never seem to stay in one place.
Elder User
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O is a perfect value for either STFT or LTFT so be glad you LTFT is 0 instead of max lean or rich. When the LTFT goes max lean or rich and the STFT also goes to max in the same direction there is no more adaptive strategy left and a DTC is going to be set. If your trims are jumping all over the place whether your spraying or not there's no need to spray. Why not just deal with B1S1 and B2S1 for now and leave the post cats for later. This means you have one bank lean and the other rich. There are two ways too look at lean and rich. Lean can be too much air or not enough fuel and surprisingly rich can mean the same thing. If you're above 14.7 you're lean and if your below 14.7 you're rich. Vacuum leaks due to bad hoses or gasket, fuel pump, fuel filter, fuel regulator, faulty (not opening) or leaking injectors. There are many more.
Elder User
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Are your O2s switching? They should repeatedly transition above and below 0.450mVdc. You didn't mention what scan tool you're using. Can you display your O2 outputs as an o scope waveform or a voltage. If so do it and watch for the 0.450mVdc switching. They will go from about 0.300mV passing 0.450mV then to around 0.700mV then back to 0.350mV and repeat over and over aging. If you see this switch your O2s are OK unless the switching is very slow in which case you might get an insufficient switching DTC which you don't have. Yours are misfire DTCs. With as many problems as you have don't rule anything out including the intake. If your misfire DTC are at the top of the list work on those. Do you have a procedure for troubleshooting a misfire DTC? You need one. Do you know what could cause a misfire DTC on a specific cylinder. At least you know what cylinders to work on rather than having P0300.
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I can honestly say that I think the misfires are related to the lean condition. But, whether I am wrong or not, I am going to try to fix the lean condition first.
My OBDII reader isn't the best, it's the schucks/checkers/kragen special. I've got live data, but limited info. I'll look to see if I have voltage readings on the O2 sensors.
My OBDII reader isn't the best, it's the schucks/checkers/kragen special. I've got live data, but limited info. I'll look to see if I have voltage readings on the O2 sensors.
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Update, for all of you who have been eagerly awaiting...
I found a 1/4" hole in the 90 degree rubber hose that goes into the throttle body off of a hard line from the pcv. I've heard of other people saying that their pcv hoses have worn through. Mine was at the TB, others were at the pcv. So, if you're having these problems, make sure you check both places. I couldn't even see this rubber hose until I lifted the upper intake manifold up. (I was preparing to replace the intake manifold gaskets.)
I hope this fixes my misfire DTCs as well. We'll see...
I found a 1/4" hole in the 90 degree rubber hose that goes into the throttle body off of a hard line from the pcv. I've heard of other people saying that their pcv hoses have worn through. Mine was at the TB, others were at the pcv. So, if you're having these problems, make sure you check both places. I couldn't even see this rubber hose until I lifted the upper intake manifold up. (I was preparing to replace the intake manifold gaskets.)
I hope this fixes my misfire DTCs as well. We'll see...
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