When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Well with your scan tool if you have one is to look at your IAT then disconnect the AIR fitting and see if the IAT is now lower…if it is lower then that is most likely your issue and no need to do a back pressure reading…curious what your fuel trims look like and your driveability issues like your idle surging…you may have negative trims on the left back and positive on the right side.
I'm having a hard time seeing a correlation between the IAT and left bank AIR check valve. It's clear to me how you could measure back pressure at the disconnected check valve in the event the cat is partially clogged. I do not see a path for intake air temp to be impacted by the increased CAT temp.
I'm having a hard time seeing a correlation between the IAT and left bank AIR check valve. It's clear to me how you could measure back pressure at the disconnected check valve in the event the cat is partially clogged. I do not see a path for intake air temp to be impacted by the increased CAT temp.
I said you measure back pressure at the check valve instead of at the O2 sensor…if the cat is restricted where is that hot exhaust gas going ??…it’s not going out the tailpipe.
I said you measure back pressure at the check valve instead of at the O2 sensor…if the cat is restricted where is that hot exhaust gas going ??…it’s not going out the tailpipe.
113*F and 125*F are typical heat soaking temperature. Relocate the IAT to just before the throttle body. Use a high quality GM sensor with a plastic isolation washer. Furthermore to aid in diagnostics you may wish to add a 1500Ohm variable resistor to the IAT wires (either wire, inline) so you can manually play with and adjust the IAT for timing compensation as desired. 1500Ohms is worth about 14 to 18*F, its not linear with respect to the starting point, the hotter you are the more influence it has.
A true solution to underhood heating of intake system air is
1. cold air ducting (NOT cold air intake system, use the same old FILTER just get lower temp induction if possible)
2. Thermal barriers around the engine e.g. exhaust wrap, ceramic coatings, blankets, shields, sheaths, etc...
3. I don't recommend heat extraction venting because it is an uncontrollable energy leak when the engine has no insulation. But if it helps in a pinch... a small hole somewhere...
Imbalance a/f ratio can be caused by many things, such as clogged injectors. As routine maint probably clean the injectors, new spark plugs, wires, do a general tune up. Get a fresh start on consumables to rule them out of your variation in diagnostics, prevent wasted time.
The most responsible way to lower IAT is to insulate the engine. Lower underhood heating = lower IAT. The intake manifolds LS1/LS6 plastic surface should run around 125*F Iirc. That is typical temperature from my recollection. You can check with a IR gun any LS1 intake manifold. The highest IAT you should see during WOT is around 110*F usually. If you are more than 115*F during WOT then that is some oddity and a possible problem. It is normal however for IAT to creep up during sitting, heat soaking, due to location and contact surface area, as nearby heating, and especially when shut off and sitting in the hot sun mid-day it can reach 130 140*F
Def follow through diag wit hthe cat, I don't normally tune cars with cats and air system I mostly deal with extremely modified engines without those items. I'm not distracting you from that diagnostic I'm just supplementing with ideas and followthrough
I just went back checked my shielding video my actual intake LS1 surface temps are around 150 to 160*F, My air filter is under the hood but I am heavily insulated and turbocharged 600rwhp my IAT is about 108*F at wide open throttle. The IAT is rate phenomnum, phenomiom... phenomenon, the more power you make the more air you move the faster it comes from outside without getting heated as much. I suppose its sort of like a self fulfilling prophecy as the power increases the rate of air ingested increases and has less time to warm on its way to the engine making the air density better and better as you increase power more and more. So... yeah. Add a supercharger and your problems go poof I bet. hehe... up in smoke
[QUOTE=C5 Diag;1607896932]Video by John Thornton the top automotive instructor in the country…IAT and restricted exhaust…start at the 17:30 minute mark.
/QUOTE]
More pieces to the puzzle. This morning I got up early while there was no traffic and it was cool outside. I decided to take a short drive with the scan tool recording the live data. Ambient temp was 66, IAT was 77 degrees. It was running amazing, pulling hard, responsive..
Then about 15 minutes in, the scanner beeped and the I/M light came on. It said there was a Fuel System 2 CL-Fault, and my fuel trims went nuts.
SFT at 24. No CEL or MIL, but it threw two pending codes. I had this code once back in February after the car had been in the garage most of the winter, but I cleared it and it didn't return until this morning. I assume this is why the fuel trims are off the charts. I can totally smell cats burning.
I brought it home and parked it. I'll clear the codes tonight and give it another cold-start sequence in the morning. If it does it again, does this mean I have cooked O2 sensors? I don't know what CL-Fault means, unless that means an open circuit?
“CL” means “Closed Loop” which means the PCM uses the O2 sensors for fueling strategy…in “OL” the PCM uses inputs like ECT, IAT, TPS, MAP for fueling strategy…O2’s are not used….yes a restricted exhaust can set a P0300 which is a random misfire…P0161 is an issue with the downstream O2 sensor either a bad sensor (heater circuit) or a wiring issue…these 2 DTC’s are “2 trip faults” which means during the next ignition cycle if they reoccur it will go from pending to current.
O2 sensors especially narrowbands behave as a product of mechanical balance in the fuel/air distribution/combustion of an engine. Remember they are averaging several cylinders.
A misfire in any cylinder can throw off an entire bank, O2 sensors will detect unreacted oxygen present
'O2 heater circuit' seems to point to the wiring and oxygen sensor itself. But this would not lead to a misfire unless a cylinder has been fouled previously. Or has some air leaking at the intake manifold port. Or some issue with spark delivery. Or perhaps bad gas stuff like that.
I will tentatively suggest your heater circuit malfunction is perhaps a bad oxygen sensor consuming excess current. This and the conditions of the spark plugs from running an unknown mixture and unknown problems is why I mentioned tune-up. Replace the oxygen sensor and inspect some spark plugs on either side is a kind of first trial and error.
A misfire could be caused by excess exhaust gas pressure due to clogged exhaust one side which is what C5Diag showing in that video. I'm not sure if it can damage an O2 heater element or what that has to do with it, maybe coincidence.
You might be able to see the exhaust clog in a compression test by comparing sides if that is what it is. I doubt it but its not hard to try.
If we assume there is no exhaust restriction, the followup is to replace oxygen sensors and spark plugs, and inspect the plugs for differences. Then the rest of a tune-up.
If you are not replacing tune-up items and inspecting spark plugs you do not know what sort of decay and long term wear/damage has been done previously which is influencing your results and diagnostics now.
The random sort of its runs fine then suddenly has some faults, does not sound like a blocked exhaust system to me, I wouldn't think it would be intermittent. But maybe a cat can do that sort of thing when it heats up, perhaps some of the materials inside are loose and sort of crumbling around blocking the cat inside guessing
The crazy fuel trims are from whatever is ailing the oxygen sensors - a leak into the exhaust system, a failed oxygen sensor(s), a misfire due to the things I listed or other.
Strongly recommend a compression test on at least 1 cylinder from each side.
O2 sensors especially narrowbands behave as a product of mechanical balance in the fuel/air distribution/combustion of an engine. Remember they are averaging several cylinders.
A misfire in any cylinder can throw off an entire bank, O2 sensors will detect unreacted oxygen present
'O2 heater circuit' seems to point to the wiring and oxygen sensor itself. But this would not lead to a misfire unless a cylinder has been fouled previously. Or has some air leaking at the intake manifold port. Or some issue with spark delivery. Or perhaps bad gas stuff like that.
I will tentatively suggest your heater circuit malfunction is perhaps a bad oxygen sensor consuming excess current. This and the conditions of the spark plugs from running an unknown mixture and unknown problems is why I mentioned tune-up. Replace the oxygen sensor and inspect some spark plugs on either side is a kind of first trial and error.
A misfire could be caused by excess exhaust gas pressure due to clogged exhaust one side which is what C5Diag showing in that video. I'm not sure if it can damage an O2 heater element or what that has to do with it, maybe coincidence.
You might be able to see the exhaust clog in a compression test by comparing sides if that is what it is. I doubt it but its not hard to try.
If we assume there is no exhaust restriction, the followup is to replace oxygen sensors and spark plugs, and inspect the plugs for differences. Then the rest of a tune-up.
If you are not replacing tune-up items and inspecting spark plugs you do not know what sort of decay and long term wear/damage has been done previously which is influencing your results and diagnostics now.
The random sort of its runs fine then suddenly has some faults, does not sound like a blocked exhaust system to me, I wouldn't think it would be intermittent. But maybe a cat can do that sort of thing when it heats up, perhaps some of the materials inside are loose and sort of crumbling around blocking the cat inside guessing
The crazy fuel trims are from whatever is ailing the oxygen sensors - a leak into the exhaust system, a failed oxygen sensor(s), a misfire due to the things I listed or other.
Strongly recommend a compression test on at least 1 cylinder from each side.
Thinking P0161 is just a coincidence…either using a vacuum gauge or looking at the MAP sensor on scan tool under load or actually hooking up a back pressure gauge is the way to go…I’m lazy so I’d hook up my First Look Sensor or Pressure Transducer without having to crawl underneath the car to hook up a back pressure gauge down there.
Thinking P0161 is just a coincidence…either using a vacuum gauge or looking at the MAP sensor on scan tool under load or actually hooking up a back pressure gauge is the way to go…I’m lazy so I’d hook up my First Look Sensor or Pressure Transducer without having to crawl underneath the car to hook up a back pressure gauge down there.
oo so much fancy tools. I don't know how people put up with those scan tools. Insert joke about gutted cats being equivalent to all of those diagnostic tools.
oo so much fancy tools. I don't know how people put up with those scan tools. Insert joke about gutted cats being equivalent to all of those diagnostic tools.
So, some heat wrap similar to what guys put around their headers?
One more question. If heatsoak is an issue, do headers make it worse from more radiant heat? Or do they make it better with more flow? I assume moving the IAT isn't going to gain me more than a couple HP then. I was looking to see where I left about 50-75 on the table. The cam is supposed to run 450 WHP. On a good cold day with plenty of headwind, I might crack 400. She's making 390 on the dyno.
No header wrap, use a foil faced insulation. The foil will reflect the radiant heat away from the air inlet tube. This is not the magic bullet to solve your reduced power, though it will reduce your IAT's. Save this for one of the last things you do.
As far as headers making more radiant heat, Yes they do. This is why half the wiring loom gets melted in the engine bay.
Thinking P0161 is just a coincidence…either using a vacuum gauge or looking at the MAP sensor on scan tool under load or actually hooking up a back pressure gauge is the way to go…I’m lazy so I’d hook up my First Look Sensor or Pressure Transducer without having to crawl underneath the car to hook up a back pressure gauge down there.
The power went out for four hours yesterday, so there was nothing else to do but jack it up and put it on jack stands. The downstream O2 wires on both banks look pretty old and crunchy. I imagine all the heat I added from the cam and tune didn't help. I saw the H-pipe just tossed on the floor when the shop was building it. I think the mechanic expected I would put headers on it while he had the engine out, but I chose to not fight the EPA for now. I think the wires were already fragile and disturbing the H-pipe caused it to throw intermittent pending codes, which also made it dump gas cranking my fuel trims. I would have never seen this if I didn't run the scan tool while I drove yesterday.
I reset the codes last night and rode it hard this morning for an hour and a half. It had no pending codes when I got back, and it drove amazing like it usually does. I am going with an intermittent downstream O2 sensor for now. A pair of them is only 40 bucks. Harbor Freight has a vacuum kit for $12. I am going to pick one up today. I figure the easiest place to check is the elbow in the exhaust manifold right before the flange. I can reach both sides just taking the front tires off. I'll drill the hole and install the fitting there. I know the cats aren't going to last forever, and the plan is to replace the whole thing with the Magnaflow anyway. I may as well periodically check the vacuum until I do to see just how plugged the cats are. I watched some YouTube videos about checking vacuum at the intake, but couldn't really find a place to do that on the LS1. I only see crankcase ventilation hoses that seem to be in front of the blade.
I'll post the vacuum numbers as soon as I get them.
O2 sensors especially narrowbands behave as a product of mechanical balance in the fuel/air distribution/combustion of an engine. Remember they are averaging several cylinders.
A misfire in any cylinder can throw off an entire bank, O2 sensors will detect unreacted oxygen present
'O2 heater circuit' seems to point to the wiring and oxygen sensor itself. But this would not lead to a misfire unless a cylinder has been fouled previously. Or has some air leaking at the intake manifold port. Or some issue with spark delivery. Or perhaps bad gas stuff like that.
I will tentatively suggest your heater circuit malfunction is perhaps a bad oxygen sensor consuming excess current. This and the conditions of the spark plugs from running an unknown mixture and unknown problems is why I mentioned tune-up. Replace the oxygen sensor and inspect some spark plugs on either side is a kind of first trial and error.
A misfire could be caused by excess exhaust gas pressure due to clogged exhaust one side which is what C5Diag showing in that video. I'm not sure if it can damage an O2 heater element or what that has to do with it, maybe coincidence.
You might be able to see the exhaust clog in a compression test by comparing sides if that is what it is. I doubt it but its not hard to try.
If we assume there is no exhaust restriction, the followup is to replace oxygen sensors and spark plugs, and inspect the plugs for differences. Then the rest of a tune-up.
If you are not replacing tune-up items and inspecting spark plugs you do not know what sort of decay and long term wear/damage has been done previously which is influencing your results and diagnostics now.
The random sort of its runs fine then suddenly has some faults, does not sound like a blocked exhaust system to me, I wouldn't think it would be intermittent. But maybe a cat can do that sort of thing when it heats up, perhaps some of the materials inside are loose and sort of crumbling around blocking the cat inside guessing
The crazy fuel trims are from whatever is ailing the oxygen sensors - a leak into the exhaust system, a failed oxygen sensor(s), a misfire due to the things I listed or other.
Strongly recommend a compression test on at least 1 cylinder from each side.
I may pull one of the plugs on bank 2 just to see if it is getting fouled. They are NGKs with less than 3000 miles on them. I replaced them and the wires during the build. I am pretty sure I have plenty of compression. It just runs to well to have issues with internals. I have had issues with grounds and cooked wires since the build, though. The starter solenoid wire was the first to go. Now it appears the O2 harness is getting crispy. I agree with your analysis of the intermittent issues. During my early morning run today, it pulled as hard as it ever has, exhaust sounds great, etc. However, I do know I left power on the table when I didn't change the exhaust out. It's going to have to be done eventually. I am just thinking it doesn't have to be today. I am going with the O2 harness. It's a $40 part, and see where we go from there.
The “downstream” O2 sensors do NOT control fueling…the upstream sensors do !!…downstreams only monitor the cats…why are you buying a vacuum gauge ??…if you are trying to check back pressure before the cat you need a pressure gauge…like I mentioned 2 psi max at 2000 RPM…a clogged cat is an effect and NOT the cause of your issue…if you have an issue like a rich mixture, misfires, coolant or oil getting into the cats your new cats will soon be “nuked” !!…get that issue fixed THEN install your new cats !!…and where are you buying your O2 sensors from ??…$40.00 a pair ??…don’t buy them off Amazon or EBay !!…go buy some Denso’s or AC Delco from NAPA or Autozone if they carry them…watch the video !!
[QUOTE=C5 Diag;1607901506]The “downstream” O2 sensors do NOT control fueling…the upstream sensors do !!…downstreams only monitor the cats…why are you buying a vacuum gauge ??…if you are trying to check back pressure before the cat you need a pressure gauge…like I mentioned 2 psi max at 2000 RPM…a clogged cat is an effect and NOT the cause of your issue…if you have an issue like a rich mixture, misfires, coolant or oil getting into the cats your new cats will soon be “nuked” !!…get that issue fixed THEN install your new cats !!…and where are you buying your O2 sensors from ??…$40.00 a pair ??…don’t buy them off Amazon or EBay !!…go buy some Denso’s or AC Delco from NAPA or Autozone if they carry them…watch the video !!
/[QUOTE]
Got a hold of a lift today. Drilled holes in both manifolds upstream of the cats. Never got above 1 lb. of pressure at any RPM. Even WOT.
Near Zero at idle.
Drove it hard for 90 minutes before testing. Surface temp on the inlet weld was 820 degrees on bank 1 and 860 degrees on bank 2. Outlet was 970 on B1 and 982 on B2.
Everything looks in order and it flows well and still makes great power when up to temp. I am back to the intake. The first gen LS1 intake and TB has got to be what is holding me back.
One thing I did wonder about, the downstream 02 sensors cross the wires over and plug into harnesses on the opposite side, so the B2 cat 02 wire runs along the exhaust shield, and then crosses over and plugs into a harness on bank 1, and vice-versa. Is this correct? Or did the shop that built my engine switch them inadvertently?
[QUOTE=dainon;1607919421][QUOTE=C5 Diag;1607901506]The “downstream” O2 sensors do NOT control fueling…the upstream sensors do !!…downstreams only monitor the cats…why are you buying a vacuum gauge ??…if you are trying to check back pressure before the cat you need a pressure gauge…like I mentioned 2 psi max at 2000 RPM…a clogged cat is an effect and NOT the cause of your issue…if you have an issue like a rich mixture, misfires, coolant or oil getting into the cats your new cats will soon be “nuked” !!…get that issue fixed THEN install your new cats !!…and where are you buying your O2 sensors from ??…$40.00 a pair ??…don’t buy them off Amazon or EBay !!…go buy some Denso’s or AC Delco from NAPA or Autozone if they carry them…watch the video !!
/
Got a hold of a lift today. Drilled holes in both manifolds upstream of the cats. Never got above 1 lb. of pressure at any RPM. Even WOT.
Near Zero at idle.
Drove it hard for 90 minutes before testing. Surface temp on the inlet weld was 820 degrees on bank 1 and 860 degrees on bank 2. Outlet was 970 on B1 and 982 on B2.
Everything looks in order and it flows well and still makes great power when up to temp. I am back to the intake. The first gen LS1 intake and TB has got to be what is holding me back.
One thing I did wonder about, the downstream 02 sensors cross the wires over and plug into harnesses on the opposite side, so the B2 cat 02 wire runs along the exhaust shield, and then crosses over and plugs into a harness on bank 1, and vice-versa. Is this correct? Or did the shop that built my engine switch them inadvertently?
Yes, the O2 harness from the right side plugs into the connector on the left side bank 1…is that gauge accurate ??
