Backfiring through the throttle body
#21
12-20-2014, 11:30 PM
Legend
-36.6% is not too far out of line, but means there's a ton of fuel going in the motor when there shouldn't be, OR it's not getting burned efficiently.
During these same windows, what is the ignition timing doing? If it's going dead rich, it should be adding timing and taking fuel away (the negative STFT). I have a hot tune from Sean plus an MSD, and my PCM reported timing is usually between 35 and 45 degrees, minus the 10 degrees I take out via the MSD box when on pump gas. I think stock should be between 25 and 35 (What I should be around with the 10 taken out in the box).
Cherokee @ -36%: http://www.cherokeeforum.com/f2/bad-...3/#post2627059
http://www.easterncatalytic.com/educ...agnostic-tool/
During these same windows, what is the ignition timing doing? If it's going dead rich, it should be adding timing and taking fuel away (the negative STFT). I have a hot tune from Sean plus an MSD, and my PCM reported timing is usually between 35 and 45 degrees, minus the 10 degrees I take out via the MSD box when on pump gas. I think stock should be between 25 and 35 (What I should be around with the 10 taken out in the box).
Cherokee @ -36%: http://www.cherokeeforum.com/f2/bad-...3/#post2627059
* When the [STFT] numbers are negative, the computer is subtracting fuel to compensate for a rich mixture. The most likely reason is a dripping injector. This will drive the other cylinders extremely lean, almost to the border-line of misfiring. The result is that on quick acceleration from a dead stop, the engine may hesitate, stumble and stall.
A leaky injector will be less detrimental at higher speed (2000), since the number of drips is only 30% of what it would be at idle. To prove this, increase speed to 2000 RPM and observe the short term percentage number dropping toward zero.
** Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
A leaky injector will be less detrimental at higher speed (2000), since the number of drips is only 30% of what it would be at idle. To prove this, increase speed to 2000 RPM and observe the short term percentage number dropping toward zero.
** Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Short Term Fuel Trim
Short Term Fuel Trim (STFT1 and STFT2) is the computer’s immediate response to adjust the air/fuel ratio. In positive corrections, fuel is added to adjust for a lean condition, while negative corrections respond to a rich condition. STFT corrections represent the current engine run cycle and react very quickly to O2 sensor input. If you were to create a large vacuum leak at Idle by disconnecting the PCV hose, the computer would immediately add positive fuel trim to balance the mixture. Short Term Fuel Trim is not stored in Keep Alive Memory (KAM) after shut down and automatically resets to 0 for the next start/run cycle.
Long Term Fuel Trim
Unlike STFT, Long Term Fuel Trim (LTFT1 and LTFT2) is learned over time while in closed loop operation. It is stored in the KAM and also used for open loop fuel calculations (like start up and wide
open throttle). LTFT is a coarser adjustment and also works to keep STFT within specification.
Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
Short Term Fuel Trim (STFT1 and STFT2) is the computer’s immediate response to adjust the air/fuel ratio. In positive corrections, fuel is added to adjust for a lean condition, while negative corrections respond to a rich condition. STFT corrections represent the current engine run cycle and react very quickly to O2 sensor input. If you were to create a large vacuum leak at Idle by disconnecting the PCV hose, the computer would immediately add positive fuel trim to balance the mixture. Short Term Fuel Trim is not stored in Keep Alive Memory (KAM) after shut down and automatically resets to 0 for the next start/run cycle.
Long Term Fuel Trim
Unlike STFT, Long Term Fuel Trim (LTFT1 and LTFT2) is learned over time while in closed loop operation. It is stored in the KAM and also used for open loop fuel calculations (like start up and wide
open throttle). LTFT is a coarser adjustment and also works to keep STFT within specification.
Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
Last edited by magnethead; 12-20-2014 at 11:45 PM.
#22
12-21-2014, 02:02 AM
I had some weird idle and takeoff problems for about a year and had a two year old TPS in it so I didn't think it could be the TPS but everything pointed to the TPS. I finally decided to replace it as everything pointed to the TPS and what do you know all my problems vanished.
Get an OEM brand or a good name brand TPS like airtex wells see if things improve.
Get the more expensive airtex wells not the cheap model
One other thing you may want to check is if you have binding, rubbing going on with the throttle cable or something binding in the throttle body.
Is the throttle body functioning smoothly/properly or is binding going on.
Get an OEM brand or a good name brand TPS like airtex wells see if things improve.
Get the more expensive airtex wells not the cheap model
One other thing you may want to check is if you have binding, rubbing going on with the throttle cable or something binding in the throttle body.
Is the throttle body functioning smoothly/properly or is binding going on.
Last edited by 98DAKAZ; 12-21-2014 at 02:04 AM.
#23
05-21-2015, 06:02 PM
Given the mileage that I have, I'm sure those gaskets need changed. Yeah, I saw an aftermarket plenum plate made out of 1/4" aluminum plate that's guaranteed to fix the leak and keep it fixed. I think it was from hughesengines.com. I also plan to replace every vacuum line I can find to try to eliminate any possible vacuum leaks. Did you have any trouble getting the distributor reinstalled correctly? Right now, that would be my main concern. The rest would be a piece of cake.
#24
05-22-2015, 12:06 PM
Join Date: Mar 2014
Location: Danville, IN
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I'm sure that the plenum leak issue has been resolved. A friend of mine has given me the name of a guy that he says is a wiz on the type of problem I'm having. I've decided to take it to him to see what he says about it because, quite frankly, this is starting to get beyond my knowledge and expertise.
#25
07-11-2017, 10:07 PM
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I'm reviving this old thread because I think I finally figured out the answer to the problem I was having.
For the past 2 YEARS I had this problem of the truck's short term fuel trim bottoming out going lean upon restart after driving it. When I would try to give it the gas, it would stumble and backfire through the throttle body. Obviously that was due to the lean condition. I stumbled upon a discussion in a forum somewhere else on the web that made me think that this could be my problem. The discussion was about O2 sensors and which would work best for my truck. Almost everyone was saying that the Bosch O2 sensors were junk and didn't work in a Dodge truck. Almost everyone agreed that the Denso brand worked the best. As it turned out, Bosch is what I had in my truck. So I decided to order all 4 Denso O2 sensors from Rockauto and give them a try.
I ordered:
Denso #234-4767 (downstream, left)
Denso #234-4771 (downstream, right)
Denso #234-4770 (upstream, right)
Denso #234-4766 (upstream, left)
I installed these O2 sensors this past Sunday. I've been driving the truck and so far, it has been running perfectly. Not even a hiccup. Idle is even smooth when previously it was a little shaky and uneven. It's my understanding that Denso is the OEM brand. Everything is fine right now but I've only been driving it for two days. Unless I start having more problems, I'm going to call this a fix.
For the past 2 YEARS I had this problem of the truck's short term fuel trim bottoming out going lean upon restart after driving it. When I would try to give it the gas, it would stumble and backfire through the throttle body. Obviously that was due to the lean condition. I stumbled upon a discussion in a forum somewhere else on the web that made me think that this could be my problem. The discussion was about O2 sensors and which would work best for my truck. Almost everyone was saying that the Bosch O2 sensors were junk and didn't work in a Dodge truck. Almost everyone agreed that the Denso brand worked the best. As it turned out, Bosch is what I had in my truck. So I decided to order all 4 Denso O2 sensors from Rockauto and give them a try.
I ordered:
Denso #234-4767 (downstream, left)
Denso #234-4771 (downstream, right)
Denso #234-4770 (upstream, right)
Denso #234-4766 (upstream, left)
I installed these O2 sensors this past Sunday. I've been driving the truck and so far, it has been running perfectly. Not even a hiccup. Idle is even smooth when previously it was a little shaky and uneven. It's my understanding that Denso is the OEM brand. Everything is fine right now but I've only been driving it for two days. Unless I start having more problems, I'm going to call this a fix.
#26
11-17-2020, 11:31 PM
Same issue
I'm sure that the plenum leak issue has been resolved. A friend of mine has given me the name of a guy that he says is a wiz on the type of problem I'm having. I've decided to take it to him to see what he says about it because, quite frankly, this is starting to get beyond my knowledge and expertise.