P0171/4 Codes - About to torch the car...
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Teching In
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P0171/4 Codes - About to torch the car... So I know this issue has been discussed at length and Ive browsed so many threads and tried so many things I'm about at my wits end.
Car is an 87 IROC-Z, engine was pulled from a 2003 GMC Savana van, 4.8L, 4L80e including full harness and computer, sent the ecu out to have emissions and rear O2's deleted, came back and engine ran perfect, at time of install one year ago I installed a new fuel pump and FPR, engine has been running fine up until one day it fell on it's face as I pulled onto the highway, a couple minutes later the codes popped up, luckily I only had a couple miles to go to get home.
symptoms - rough idle, hard to start, would almost die if given any throttle
replaced MAF sensor with new - no change in condition
checked vacuum lines and replaced all - no change in condition
replaced intake gaskets - wont start AT ALL now
checked fuel pressure at rail - 58 psi steady
checked signal to all fuel injectors with noid lights - all firing
checked all coils and plugs - all firing
checked exhaust, no leaks - true dual from headers back so wouldn't think both banks would go at once
thought it possibly could be O2 sensors but not sure they would both go at the exact same time
also accidently cleared codes and since it wont start now cant check freeze frame data
I'm stuck on where to look next and in dire need of some advice
Car is an 87 IROC-Z, engine was pulled from a 2003 GMC Savana van, 4.8L, 4L80e including full harness and computer, sent the ecu out to have emissions and rear O2's deleted, came back and engine ran perfect, at time of install one year ago I installed a new fuel pump and FPR, engine has been running fine up until one day it fell on it's face as I pulled onto the highway, a couple minutes later the codes popped up, luckily I only had a couple miles to go to get home.
symptoms - rough idle, hard to start, would almost die if given any throttle
replaced MAF sensor with new - no change in condition
checked vacuum lines and replaced all - no change in condition
replaced intake gaskets - wont start AT ALL now
checked fuel pressure at rail - 58 psi steady
checked signal to all fuel injectors with noid lights - all firing
checked all coils and plugs - all firing
checked exhaust, no leaks - true dual from headers back so wouldn't think both banks would go at once
thought it possibly could be O2 sensors but not sure they would both go at the exact same time
also accidently cleared codes and since it wont start now cant check freeze frame data
I'm stuck on where to look next and in dire need of some advice
Last edited by Dustin Fritz; Jul 8, 2016 at 09:28 AM. Reason: aditional information
assuming computer reprogramming in not screwed up and the cause of the problem,
the O2's you should be able to disconnect and run in open loop, and you should get DTC's related to that unless the reprogramming prevents that;
not sure if MAF would cause hard start or no start, it is said disconnecting the MAF can sometimes help in troubleshooting - that it'll default to a speed density type of calculation for fueling the engine and that should allow it to run fairly well.
with handheld observe the MAP reading, if the engine is not starting then it should at least read atmospheric with key on, and when cranking with throttle closed the reading should drop... at least do a sanity check on the map reading to make sure it's valid.
otherwise i would start looking at cam and crank sensors, i think those are the most likely given your symptoms... if not a bad sensor a bad/pinched/burnt wire that's messing up that signal.
and you say all of a sudden fell on it's face, i would also inspect all the engine/PCM wiring looking for something that's chaffed or pinched.
the O2's you should be able to disconnect and run in open loop, and you should get DTC's related to that unless the reprogramming prevents that;
not sure if MAF would cause hard start or no start, it is said disconnecting the MAF can sometimes help in troubleshooting - that it'll default to a speed density type of calculation for fueling the engine and that should allow it to run fairly well.
with handheld observe the MAP reading, if the engine is not starting then it should at least read atmospheric with key on, and when cranking with throttle closed the reading should drop... at least do a sanity check on the map reading to make sure it's valid.
otherwise i would start looking at cam and crank sensors, i think those are the most likely given your symptoms... if not a bad sensor a bad/pinched/burnt wire that's messing up that signal.
and you say all of a sudden fell on it's face, i would also inspect all the engine/PCM wiring looking for something that's chaffed or pinched.
Disconnect sensors and replug them in. Then pull your plugs and see if they are fouled. Shouldn't cause the non-start, but would contribute to codes and rough running later. I had fouled plugs which resulted from two bad O2 sensors and bad MAF. I replaced the sensors, and torched the tips of the plugs until they were clean, and all is good now.
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my handheld doesn't show any live info from sensors, it's a cheapo from HF... I'll try disconnection the O2 sensors and check all the wiring and connectors again and report back...
I do have access to a tactrix cable, although their software doesn't currently support any GM vehicles so it's unable to interface with the ECU, unless someone knows of some open source software that's compatible?
I do have access to a tactrix cable, although their software doesn't currently support any GM vehicles so it's unable to interface with the ECU, unless someone knows of some open source software that's compatible?
P0171/4 If you had codes P0171 and P0174 then you had a lean condition which could be caused by low fuel pressure. You didn't say if you checked the pressure or not but I had the same problem which was pressure related. If you do find low pressure of course you will want to change the filter and check the flex lines.
TECH Resident
Joined: Mar 2012
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From: Elkridge MD
Are you using the stock regulator at the rail? Corvette regulator instead? I had this issue too, and it ended up being a bad regulator. idle was just a little rough but not bad, but under any kind of acceleration the engine was drinking more fuel than the regulator was allowing, meaning it would stumble and lose all power. As soon as the lines got back up to pressure, the condition would go away.
I don't know how the regulator works at the rails, but for me I was just able to replace the Vette regulator and it was all fixed
I don't know how the regulator works at the rails, but for me I was just able to replace the Vette regulator and it was all fixed
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yes fuel pressure is fine, see original post.
im running the stock FPR at the rails, brand new a year ago and still getting 58psi
I went out and inspected every wire, unplugged every sensor and took the intake back off again to check if i had pinched anything and didnt find any issues, reinstalled everything meticulously and plugged all sensors back in
gonna unplug O2 sensors and see if anything changes after lunch
im running the stock FPR at the rails, brand new a year ago and still getting 58psi
I went out and inspected every wire, unplugged every sensor and took the intake back off again to check if i had pinched anything and didnt find any issues, reinstalled everything meticulously and plugged all sensors back in
gonna unplug O2 sensors and see if anything changes after lunch
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TECH Resident
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From: Elkridge MD
Are you testing the pressure at idle or under throttle? Just because you have fuel pressure at idle doesn't mean you have it under throttle. Those codes indicate a lean condition in both banks. You are not getting enough fuel to the engine. Other problems may be a bad MAF, dirty injectors, bad fuel filter, or a significant vacuum leak
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I'm testing at key on since the engine wont seem to run
again - MAF is new, cant find a vacuum leak anywhere both visually and with starter fluid
Lets discuss the non-running issue and try to fix that before moving back to the codes
I've verified each coil and plug is firing, engine is at least getting fuel, pulled plugs and lightly set them in hole and fire shoots out each cylinder
again - MAF is new, cant find a vacuum leak anywhere both visually and with starter fluid
Lets discuss the non-running issue and try to fix that before moving back to the codes
I've verified each coil and plug is firing, engine is at least getting fuel, pulled plugs and lightly set them in hole and fire shoots out each cylinder
TECH Resident
Joined: Mar 2012
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From: Elkridge MD
If you have air, fuel and spark, I really have no idea why it shouldn't at least start, even if it runs poorly. If all of your sensors are functioning then the engine should at least TRY to run. Make sure your air cleaner and associated tubing is not taking in unmetered air. Another thing that MIGHT help, although I highly doubt it, is to unplug the IAC and see if the car will start without it. This only really regulates air at idle, but I suppose there's an off chance it could be affecting startup....although I would say it's a very slim chance.
From what I am hearing, the only thing I can pin it on is probably the computer itself. Make sure you didn't disconnect it by accident somehow, and if you have anywhere you can borrow another identical computer from, you can try swapping that so see if it will start/run. Even if the VATS shuts it off after a few seconds, you can still verify if the computer is causing your no start issue.
From what I am hearing, the only thing I can pin it on is probably the computer itself. Make sure you didn't disconnect it by accident somehow, and if you have anywhere you can borrow another identical computer from, you can try swapping that so see if it will start/run. Even if the VATS shuts it off after a few seconds, you can still verify if the computer is causing your no start issue.
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Sent the computer to the guy that programmed out the emissions and vats, he put it in a running vehicle and it started right up... So the computers fine...
I've replaced the maf, crank sensor, cam sensor, spark plugs, verified spark and fuel pressure while cranking... Would bad O2 sensor cause it to not start?
I've replaced the maf, crank sensor, cam sensor, spark plugs, verified spark and fuel pressure while cranking... Would bad O2 sensor cause it to not start?
No start In a word, yes bad O2 sensors can cause a no start condition but it would take a while of running rich to foul the plugs before you get a no run condition. If you have a smart phone get the Torque Pro app and a bluetooth adapter for the ALDL. This will give you real time info and you can look at the short and long term fuel trims. With the program you will be able to read and clear codes too.
On The Tree
Joined: Aug 2008
Posts: 109
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From: Memphis, Tennessee
I know the answer is probably no, but do you have CATS on this car? I know you said it is a true duel system, but when one cat failed on my 5.3 Denali (2007 model) I chased my tail for 20 hours before I thought to loosen the exhaust pipe bolts - then the truck ran fine. Once that cat was replaced the Lean codes I had been getting disappeared.
Assuming you do not have cats on this car, I would pull the plugs and see if they are gas fouled. If they are gas fouled, where is your fuel pressure regulator? You said you had an express van engine. If it still has the truck intake, does it have the return line fuel system?? If so, check the fuel pressure regulator. This regulator pulls vacuum from the engine, and when the diaphram fails, it will suck gas through the vacuum line and flood the engine. I had this problem on another LS swap I did and it took forever to finally figure out the regulator was bad. Once the regulator was replaced (and the gas fouled plugs) the car ran like a champ.
Good luck, and please update when you figure it out.
Ricky
Assuming you do not have cats on this car, I would pull the plugs and see if they are gas fouled. If they are gas fouled, where is your fuel pressure regulator? You said you had an express van engine. If it still has the truck intake, does it have the return line fuel system?? If so, check the fuel pressure regulator. This regulator pulls vacuum from the engine, and when the diaphram fails, it will suck gas through the vacuum line and flood the engine. I had this problem on another LS swap I did and it took forever to finally figure out the regulator was bad. Once the regulator was replaced (and the gas fouled plugs) the car ran like a champ.
Good luck, and please update when you figure it out.
Ricky
P0171 Wonder if the plugs are fouled enough that they will not fire under compression? Had that happen once and drove me nuts because they would fire if I took them out and grounded them. New plugs and it turned over once and fired.