2bfast Posted November 5, 2013 Report Share Posted November 5, 2013 Run the truck let it warm up to temp use a temp gun check the temp before and after the cat if its cold after the cat by a lot then you my friend have some clogged cats. Reason I know is this all has happened to me go get some high flow cats welded in and you should be fine or delete then and tune them out this is probably the best thing I think I have seen you ever post To the OP, do not throw 4 oxygen sensors at it and cleaning the MAF and TB wont cure it. Most likely you have clogged cats. Check what Aldofoshow suggested and report back Quote Link to comment Share on other sites More sharing options...
Blown 346 Posted November 5, 2013 Report Share Posted November 5, 2013 ok, ill be the first to admit, im not a pro with modern obdII engines. for the last 8 years ive been working on diesel, so this is all familiar to me, but i cant make heads or tails of what most of my scantool was telling me. using my scanner, everything seemed to be reading ok, all self-tests were ok, i didnt detect any misfires (neither did the truck), i simply used an infrared thermometer on each header primary, and theyre all firing, so i dont have a consistent misfire, if at all. the o2 sensors were running in the 374mv area, one seemed to jump around more than the others, should my scanner be able to turn on the 02 heaters to test them? all IGN fuses were good. ill ask the dumb questions because id rather do that then ruin a MAF or something. how do i clean them properly? i didnt want to just douche it in electronics cleaner, same question for the throttle body. should i remove it and clean it in parts cleaner or can i simply spray it out? heres a screenshot of what the truck had going on when the misfire code appeared: get some electrical parts cleaner and clean the MAF and the TPS sensor. I use brake clean for the TB... Quote Link to comment Share on other sites More sharing options...
misterp Posted November 5, 2013 Report Share Posted November 5, 2013 (edited) The job of the PCM is to know exactly how much oxygen is in the motor at any given instant - with that knowledge, it knows how much fuel to add in order to get clean combustion. To know how much air is in the motor, these sensors have to be working correctly: IAT, MAP, and (optionally) MAF. (The O2 sensors come into play later, in the fueling correction/trimming strategy.) Some thoughts I would consider, in no particular order - From what you tell me, it sounds like the truck is not being fueled correctly. I would guess it is running lean and cutting out at 4000+ rpm. I would verify that the MAP and IAT sensors are working right, can you monitor them with your scan tool? Make sure the IAT at cold-start matches outside temp, etc. Make sure idle MAP is a sane and steady value. Maybe you have a weak injector? A weak fuel pressure regulator? is there 52-psi measured at the fuel rail? Cleaning the TB - this is an easy job, I would go ahead and unbolt the unit from the manifold because it's sealed with a really good reusable silicone rubber gasket, and once you get it off there you will find a crap-load of buildup in the "throat" of the manifold, behind the throttle body. But in all honesty, I don't think that a dirty TB will cause an outright misfire - my TB is *very* dirty and the symptoms it displays is the RPM taking longer to return to idle, and a racy idle at times, but never an outright rough idle or misfire. Mr. P. More: O2's: The O2 DTC codes you have are HEATER performance - this means that the PCM sees that the O2 sensors are failing to physically get warmed-up fast enough. In trucks with aftermarket headers and/or gutted cats, this is a fact of life (cold O2 sensors) and we have to instruct the PCM to ignore these errors. But as you have factory cats, I am going to assume that you also have factory manifolds, too - which means to me that there is no reason for these O2 sensors to be failing to heat up and I would replace the front two as soon as you can afford and the rear two at your next financial opportunity. O2 sensors on these trucks should be replaced at 80K-miles anyways, I've seen several cases (including my own truck) where fuel mileage instantly got better after replacing aged O2 sensors. The blinking light on the dash just means that the PCM sees the crankshaft slowing down i.e. it is detecting a misfire - but you already know that in the moment you are driving the truck! I agree on using the infrared gun to verify the cats are still good, and from there check the fuel pressure regulator. I would also spend $7 and replace the fuel filter, too (it might be clogged?) Edited November 5, 2013 by Mr. P. (see edit history) Quote Link to comment Share on other sites More sharing options...
Blown 346 Posted November 5, 2013 Report Share Posted November 5, 2013 A dirt MAF can cause a mis fire code. I just did the same job to my buddies TBSS and his codes, mis fire, and reduced engine power were fixed after the MAF/TB cleaning. Quote Link to comment Share on other sites More sharing options...
crawlinss Posted November 9, 2013 Author Report Share Posted November 9, 2013 well, the backpressure tester i ordered on ebizzle showed was here when i got home from work at 1 am, so naturally i went out in the garage lol. left cat is definitely clogged. i talked to one of my tool dealers, he has a friend at the gm dealer that should be able to tune out the front o2's, i need to talk to my local exhaust guys and see if theyll weld in straight pipes, im not a fan of clamping exhaust together if i can avoid it. are there any other issues that might arise from tuning out the o2's? i have a hypertech on the truck, that wont affect anything, correct? Quote Link to comment Share on other sites More sharing options...
Blown 346 Posted November 9, 2013 Report Share Posted November 9, 2013 Tuning out the 02s will not hurt anything. You can get 02 simulators that will allow the computer to think its reading the 02's when it actually isnt. I did this with no ill effects for years. Exhaust shops cannot legally weld in off road pipe in place of the cats as it is illegal and the fines go into the thousands. Unless you have a buddy there then it wouldnt be a problem. Otherwise they wont do it unless its going to be like it was factory. Quote Link to comment Share on other sites More sharing options...
Cramer Posted November 9, 2013 Report Share Posted November 9, 2013 Tuning out the front O2's won't be a good idea. The rear O2's there isn't a problem. The fronts measure the afr pre cat and regulates everything. The post cat sensors just measure the residual that has passed the cats and tells the pcm the difference pre and post. Sent from my Motorola RAZR MAXX using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
crawlinss Posted November 22, 2013 Author Report Share Posted November 22, 2013 well guys, i got everything all straightened out. the left cat was completely clogged, cut them both out, drove it open headers to the local muffler shop, got some straight pipes welded in, then drove it to a guy my tool dealer recommended. he tuned out the cats, i drove it to work and then home, its running awesome, and is loud as hell LOL. thanks for all your help and advice!!! Quote Link to comment Share on other sites More sharing options...
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