5.3 DBW will not idle
06-14-2015, 09:57 AM
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5.3 DBW will not idle My 2003 5.3 in my 85 truck will idle for about 2 mins and then it will not idle at all until another cold start. Not showing any codes. I replaced the fuel pump the fuel regulator and it just will not idle and will tend to run like crap. The vacuum port behind the DBW throttle body I have plugged, this wouldnt be a problem would it? It will only run if i hold the peddle and let it idle at about 2,000 rpm. Please help me before i spend more cash.
06-19-2015, 03:12 PM
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Just replaced another fuel pressure regulator and still no idle and running like crap. So i got good fuel pressure and new injectors as well as all new fuel system. I just do not know where to turn.Sent the puter back for another tuning and still nothing. Where does that vacuum line behind the throttle body supposed to go?????
06-19-2015, 05:43 PM
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I am running open headers right now with front O'2s. Not getting any codes to help either. Seems to rev ok but stumbling a little. Its a new motor i just rebuilt with new gas tank and external real walbro 255.
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06-21-2015, 08:17 AM
#8
Try disconnecting the MAf and letting it run on the VE tables. Do this while it is running. You will notice a stutter, then it will start running again.
Edit-But you will not solve your problem until it is tuned. You may try a diablo tuner to see if this helps.
Edit-But you will not solve your problem until it is tuned. You may try a diablo tuner to see if this helps.
Last edited by casias; 06-21-2015 at 08:22 AM.
06-21-2015, 10:45 AM
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Anyone know anybody close to Goldsboro NC for a tune???
06-22-2015, 04:45 PM
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If you can't find a tuner that's closer to you, you might try a different mail order tuner that can do data logging like Black Bear. They can send you a roughed out custom tune along with a hand held to do the data logging so they can see what it's doing and then refine it for you. Hopefully you can figure something else out but that'd be another option for you...
06-22-2015, 05:52 PM
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If you can't find a tuner that's closer to you, you might try a different mail order tuner that can do data logging like Black Bear. They can send you a roughed out custom tune along with a hand held to do the data logging so they can see what it's doing and then refine it for you. Hopefully you can figure something else out but that'd be another option for you...
06-22-2015, 08:19 PM
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The port i'm assuming you are referring to on the rear of the engine is for brake booster. Make sure when you are running with the MAF that you have a filter on, otherwise gusts of wind or basically any wind causes issues during running.
06-22-2015, 11:55 PM
#13
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Since you said it runs ok for the first two minutes, try disconnecting both O2 sensors. This will force it to stay in open loop. If it stays running ok then the O2 sensors are messing things up. Most likely because they are reading lean (but not really) because it's open headers. This will cause the PCM to keep adding more and more fuel to try to get the O2 sensors to read rich. Which it won't because they are still reading the oxygen coming back from the open exhaust.
06-23-2015, 06:00 PM
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Since you said it runs ok for the first two minutes, try disconnecting both O2 sensors. This will force it to stay in open loop. If it stays running ok then the O2 sensors are messing things up. Most likely because they are reading lean (but not really) because it's open headers. This will cause the PCM to keep adding more and more fuel to try to get the O2 sensors to read rich. Which it won't because they are still reading the oxygen coming back from the open exhaust.
06-24-2015, 08:16 PM
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I suggest that you get a speed density tune and ditch the MAF. You will probably need to get an intake air temp sensor since most are integrated into the MAF. I'm willing to bet if disable the MAF that it will start running right. You will need an expensive tune to get the MAF running right and it only improves gas mileage a little.
06-25-2015, 03:51 PM
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Since you said it runs ok for the first two minutes, try disconnecting both O2 sensors. This will force it to stay in open loop. If it stays running ok then the O2 sensors are messing things up. Most likely because they are reading lean (but not really) because it's open headers. This will cause the PCM to keep adding more and more fuel to try to get the O2 sensors to read rich. Which it won't because they are still reading the oxygen coming back from the open exhaust.
I will try and run at least some pipes and possibly mufflers this weekend hopefully and i got new o2's on order so i got fingers crossed i am closer to driving it.
Please any more suggestions are welcome and needed at this point.
06-25-2015, 03:52 PM
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I suggest that you get a speed density tune and ditch the MAF. You will probably need to get an intake air temp sensor since most are integrated into the MAF. I'm willing to bet if disable the MAF that it will start running right. You will need an expensive tune to get the MAF running right and it only improves gas mileage a little.
06-25-2015, 07:50 PM
#18
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Do you have the vacuum port on the throttle body open to air? If so that would cause a big vacuum leak. Hook that port to the one on the front of the right valve cover. Also the port on the left rear valve cover is the pcv dirty side. Depending what intake you're running, it hooks to the top on a truck intake of the RF of a car intake.
06-26-2015, 05:39 PM
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Do you have the vacuum port on the throttle body open to air? If so that would cause a big vacuum leak. Hook that port to the one on the front of the right valve cover. Also the port on the left rear valve cover is the pcv dirty side. Depending what intake you're running, it hooks to the top on a truck intake of the RF of a car intake.
I will say I really like working on these motors the more I learn from people like yourself.
Hopefully, I can do some exhaust work this weekend and add the new o'2s..Thanx again.
