- This topic has 20 replies, 4 voices, and was last updated 11 years, 6 months ago by
.
-
Topic
-
97 Accord Ex 2.2L VTEC 5 Speed
I thought I had an exhaust leak before. The problem started when my car would stumble when letting off the gas on the highway or shifting and after checking my fuel trim it showed a high short term. At idle the fuel trim would slowly climb up to almost +50%. I would monitor my car all the time and the long term fuel trim should be -5.5% with a short term floating around that area. I did a seafoam exhaust leak test and saw smoke coming from where I had stripped the exhaust bolt. So I fixed it. And the problem still happened. So after tightening the nuts, changing the gasket and eventually getting a new manifold (thinking it was cracked) I still am having problems.
There’s no cel yet but the car is now switching in and out of closed loop. Torque (app) says its due to insufficient temperature. My coolant reads as low as 188 on the highway and the manifold is insulated to the cat so the o2 sensor heats up well. So my car isn’t getting cool enough to switch back to open loop and nothing really has changed. The o2 sensor is properly heated up by the exhaust gases. But Im not sure about the heater wire.
Both sensors will read normal and then go to opposite voltages (#1 at .1v and #2 at .8v), stay almost dead (moving maybe .3 volts back and forth) and then it’ll go to open loop. This happens repeatedly. When I get the sensor readings the fuel trim reads a lean exhaust.
Any idea what it could be if its not an exhaust leak?
I’ve calibrated the TPS before, it fine. Timing advance readings at idle would be abnormal if it werent right?
I notice that my fuel injectors are ticking much louder (no its not valve ticking, its the injectors), but thats been going on for about two months.
Most of the sensors on the car are either new (within the past year and a half) or have been taken care of and monitored
Heres my biggest question though:
Im wondering about a bad upstream sensor- but could that cause funny readings from both o2 sensors?
-
Replies
-
It’s very possible. Ideally the front sensor should switch between .2v to .8v and the post cat sensor should float around .5v . If the ECM cannot correct a lean or rich condition it will go into open loop. It looks lean to me.
I would be looking for a vacuum leak or insufficient fuel pressure or flow.
Here is a spread sheet of the data from a quick trip on the highway before realizing the issue is still there and turning around
https://docs.google.com/file/d/0B3nQTmw6qDjBa3pMb1lpeXNMclE/edit?usp=sharing
Thats interesting that the ecu would go into open loop if it cannot correct the issue. Ill look into that. Thanks.
Im curious about a vacuum leak but Im pretty meticulous about the intake. The vacuum gauge reads 23 in/hg.
The engine is using more gas and the exhaust is apparently reading lean so the ecu is dumping more gas in. It feels like it was running rich with the prior exhaust problem, now it feels like its running lean but sometimes dumping gas in randomly.
And In case anyone asks, I did reset the ecu after doing the repairs.
I should mention something weird from before but it doesn’t seem like it has caused any issues.
I did a map sensor test based on the FSM. The test said to measure the signal wire to ground and the reference wire to ground. This is with the ignition on and the connector disconnected from the map. What I read was 5 volts at the reference and ground wires like I should but at the signal and ground wire I read 4.66 volts. Its not a lot but its a difference considering .5 volts is about 5 in/hg. FSM said to check at the ECU. So I found the same color wire and it read the exact same voltage at the ECU harness. Does that seem like something that could influence this? I haven’t had much of a problem with the car despite the findings until recently.My gut says it is a vacuum leak. Check Eric videos for finding vacuum leaks.
O2 sensor typically do not get “lazy” (stop working at idle), especially if they are heated O2 sensors. It can happen, it is just not common.
Ill double check with my vacuum gauge but 23 in/hg is normal for me and I would be running lean rather than rich with a leak right?
[quote=”sjrobinson” post=66145]Ill double check with my vacuum gauge but 23 in/hg is normal for me and I would be running lean rather than rich with a leak right?[/quote]
Vacuum gauge is not accurate enough.
I missed the fact the the fuel trim was negative. Not common but sometimes injectors get partially clogged and will “dribble” even when closed,
Check Eric’s videos on cleaning injectors.
The vacuum gauge does correspond with my map sensor readings at the port and at the sensor.
But I will do that. I think fuel injectors could be an issue.
So does that explain everything?
I did notice some fuel around the banjo bolt on the filter. I did a fuel pressure test when I first had the problem, maybe it needs a new washer from when I tested it and while I had the exhaust problem fixed, the bolt was leaking fuel at high pressures causing the same issue of a lean exhaust and the car trying to dump more fuel into the system. Maybe that and the exhaust leak were both causing the same symptoms and then the ecu was shutting off the o2 sensors realizing that it could not get enough fuel into the engine based on the upstream readings.
I did another fuel leak check and my manifold is on there tight. No seafoam smoke when I clogged the tailpipe. My car is reading a bit more normal now but I haven’t driven it. Idle is a little shaky but my fuel trim readings are normal at idle and the o2 sensors are reading fine. Ill update this when I go for a drive. In the mean time any more suggestions of things to check as long as my heads under the hood?
After a drive the car is still doing it. But its intermittent. I check and the majority of the time the car is in open loop. But the o2 sensor readings seem incorrect, like theyre both defective. Its not that the ecu is ignoring them, its like the voltages are inconsistent and not accurate with the exhaust.
Id change the upstream but it wouldnt explain why the downstream acts funny too.
[quote=”sjrobinson” post=66173]After a drive the car is still doing it. But its intermittent. I check and the majority of the time the car is in open loop. But the o2 sensor readings seem incorrect, like theyre both defective. Its not that the ecu is ignoring them, its like the voltages are inconsistent and not accurate with the exhaust.
Id change the upstream but it wouldnt explain why the downstream acts funny too.[/quote]
10 to 1 odds you do NOT have an O2 sensor problem !
The downstream sensor should always follow the upstream sensor. Its whole purpose in life is to validate the upstream sensor and catalyst are working. If the 2 sensor are not in sync, that is a problem.
The ECU software will ignore the O2 sensor and go open loop if it decides that the readings are invalid. It will however, sort of “kick start” the O2 sensor by driving the air fuel ratio rich and then lean to see if it has an effect. If yes, you atr in closed loop. If no it goes back to open loop for some period of time before doing this whole thing over again.
What do you think the issue is?
This started with an obvious manifold leak, the leak was fixed and yet the problem gets worse.
What I see from the sensors and fuel trim is normal when first starting the car and letting it idle for a while, then it starts to go bad once Im driving. Engine sputter when shifting and letting off the gas and then the fuel trim goes crazy at idle after driving around. Then the o2 sensors go limp but not quite dead, open loop, and then closed loop again. Continuously.
The injector resistor box is suspect. The resistance readings were off on 3 of the 4 injector connections. Ill change the part out and see if that works.
[quote=”sjrobinson” post=66311]The injector resistor box is suspect. [/quote]
What is an “injector resistor box” ?The resistance readings were off on 3 of the 4 injector connections. Ill change the part out and see if that works.
Injectors have low resistance, less than 20 ohms. Most meters are not that accurate at low resistance.
Specifically for 90’s hondas (and Mitsubishis) they were used to allow low impedance (peak and hold) injectors to be used since they do better at high speeds but the resistor was needed as to not burn out the ecu or the injectors themselves.
While the resistance may not be incredibly accurate, it is significant that i read around 12 ohms at 3 points but 6 ohms at the 4th. The 4th is right in the middle of spec, the other 3 are double the resistance. This would explain why the problem seems like it could be injector related if the ECU sees no difference when increasing the pulse width (fuel trim) based on the o2 sensor readings and decides to ignore them and go into open loop. Especially at higher rpms where the resistor box is particularly needed. If that conclusion is correct.
- You must be logged in to reply to this topic.