- This topic has 13 replies, 5 voices, and was last updated 10 years, 6 months ago by
.
-
Topic
-
My 96 Dodge Neon throws a P0171 code.
When I’m on the highway I would get up to speed to about 70-75 and then cruse at that speed. Every time I’d let off the gas, the car would jolt like it had misfire of some sort. Doing that 2 or 3 times when then lead to a CEL. Above 70 the jolt is very noticeable. Going between 60-65, you can barely notice it. Below 60mph, no jolt. When ever I’m below 60mph I never get the CEL.
I would put my cheap reader on the car and it would come up as P0171. I’d clear the code, look for loose hoses, tighten things up, but I’d get on the highway again, letting off the gas at 70+mph a few times and the P0171 would come back.
I attached a fuel pressure gauge on the fuel rail and was reading about 50psi at idle. The service manual says it should be about 49psi. At idle, fuel pressure looks good. When I rev the engine, the needle my gauge may drop a psi or two when I initially hit the throttle but it returns to 50 instantly. With the car is off, the fuel pressure will drop down to 40 psi after about 5 mins.
Today I received a Actron CP9185 scan tool in the mail so I can get better look at the data behind the code. The freeze frame showed that ST and LT fuel trims were both above 20% at 63 mph. It also showed I had a another code for a high fuel level voltage, but no OBD code to go with it. Fuel gauge doesn’t come down off of full until you drive about 60 miles, and 1/4 tank seems to really be 1/8 tank.
I cleared the codes and took the car for a spin on the highway. This time the car didn’t do its misfire thing nor it did throw a code. It always has in the past, but the only difference today was I had the scanner plugged in. I started recording when I was on the on-ramp, and tried to let off the gas when I was at speed to see capture anything related to the misfire like symptom.
After downloading the data, my LT fuel trim was all over the place. It would be -9 in one frame and then +21 in the very next frame. Is this normal? Attached is my downloaded data.
I wonder if something is out of sync and some sensor is updating fast enough when I let go of the gas or there is some issue with my fuel pump.
Any ideas?
-
Replies
-
I hate to go to fuel pump right away… but when you said you hit the gas and the fuel pressure dropped (instead of increase) this leads me to think there is a problem with the fuel pump/fuel delivery system…
When WOT is hit, the pressure should go up and then drop to a consistent level (from factory manual, not drop immediately)… I think that is what you are saying…
Fuel delivery issues can cause a P0171…Since issues are happening at high speed/high fuel delivery there may be a fuel delivery issue…
Most times a P0171 is caused by a vacuum leak, MAF issue or other, but that generally manifests itself at idle with a high idle and other issues…
JMHO
-Karl
looks to me like your car is never going into open loop. I’m gonna call some bad o2 sensors here but It would be better if the data was graphed. Good on you for posting it regardless.
[quote=”quickNpainless” post=99826]looks to me like your car is never going into open loop. Bad O2 sensors[/quote]
Perhaps you mean “closed loop”?
-Karl
It’s possible that you have a failing O2 sensor that’s not bad enough to set a code for it. You need to find someone knowledgeable to to scope it for you.
[quote=”ToyotaKarl” post=99827][quote=”quickNpainless” post=99826]looks to me like your car is never going into open loop. Bad O2 sensors[/quote]
Perhaps you mean “closed loop”?
-Karl[/quote]
yea that. what he said
[quote=”quickNpainless” post=99826]looks to me like your car is never going into open loop. I’m gonna call some bad o2 sensors here but It would be better if the data was graphed. Good on you for posting it regardless.[/quote]
In the data, Frames 11-14 show an open loop while the rest are closed.
[quote=”quickNpainless” post=99829][quote=”ToyotaKarl” post=99827][quote=”quickNpainless” post=99826]looks to me like your car is never going into open loop. Bad O2 sensors[/quote]
Perhaps you mean “closed loop”?
-Karl[/quote]
yea that. what he said[/quote]
Anything is possible with a Chrysler 😛
-Karl
But it did close… And the O2S11 is reading lean….. so what… We know there is a lean condition…. Point proven…
-Karl
[quote=”HarryOfAllTrades” post=99830][quote=”quickNpainless” post=99826]looks to me like your car is never going into open loop. I’m gonna call some bad o2 sensors here but It would be better if the data was graphed. Good on you for posting it regardless.[/quote]
In the data, Frames 11-14 show an open loop while the rest are closed.[/quote]
yea for some reason I had open and closed loop switched around in my head. Derp moment.
it’s really hard to tell if the o2 sensors are operating correctly with this kind of data (at least for me). Usually I either look at a graph or an analog voltmeter.
I also have no idea how to read raw map data so there could be something there. I can’t seem to google up any specs for the dodge neon map sensor.
No prob…. We all want to solve the riddle before others….
Good work man, you can at least read and interpret….. see my above post…
Your move…
-Karl
As pointed out that code usually means a vacuum leak or possibly an exhaust leak near the O2 sensor. It may not be a bad idea to check for vacuum leaks just to check that off the list of suspects. I’m with ToyotaKarl though, a drop in fuel psi usually means a fuel delivery issue. Perhaps change the fuel filter if you haven’t already and recheck.
You might also find this information helpful.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted on your progress.
I have an update.
I was trying to nail down the possible cause of this. I decide to do a quick test using the scan tool. From a cold start, I monitored how long it would take for the car to get into a closed loop. It about 60 seconds at idle. At 20 seconds or so, the voltages of the upstream O2 would finally move. The downstream O2 sensor responded faster than the up stream, which is weird, because I taught downstream O2 sensors where generally slower. As a comparison, I started my other car which is a newer Ford Focus to see what it would do. It went into closed loop within 2 seconds from a cold start. This was enough evidence for me to at least try an O2 sensor.
Later on in the day, I had to take my Neon out on the Highway to visit some friends. Instead of throwing a lean code, it instead threw misfire code. On the way home I bought 4 new spark plugs ($1.73 each) and a new O2 sensor ($40). Now from a cold start, the Neon goes into closed loop with in 2 seconds just like the other car. I took it for a test drive today and no codes.
Hopefully it should be fixed for now. I’ll have to keep an eye on this.
Thank you everyone for your input and help.
- You must be logged in to reply to this topic.