Puzzle: vacuum leak, injector crud, or O2 sensor fail?

[user removed]

Originally Posted by California98Civic

Amazingly, I appear to have solved the problem from a "surprise" direction. I was wishing for a mechanical vacuum gauge because it seems odd to always rely on the mediation of the UltraGauge or my OBD2 diagnotic reader thing. Then I remembered someone saying cleaning old grounds can help the car run. Then I remembered cleaning the grounds has been on my list of long-procrastinated maintenance for a year or two. Then I took 30 mins to clean engine ground, transmission ground, battery ground, and one other grounding cable. And.... PROBLEMS ARE GONE! Just pulled nearly 70mpg in traffic on a 30 mile test run. Mostly normal fuel trim for a car doing a lo of P&G (slightly on the + side by 2 or 3%). Wow. They had not been cleaned since 1998. Hahaha!

BTW, I also got fuel system cleaner, Mech. What the hell, it can't hurt. I bought a big bottle to use in each tank for a few months. Thanks!

Fantastic. I like to polish the connection areas and dab a little grease on them. Never had to redo one with that procedure. I got 6 bottles of techron at Costco for $20, supposedly the ticket for the wife's direct injected Sorento (Kia relabels the bottles). Saved me pulling the rail on the Sentra which requires pulling the upper manifold.

regards
mech

[California98Civic]

Originally Posted by Chrysler kid

Use marvel mystery oil as a fuel additive it works great in Hondas

Thanks, both of you. I actually have MMO already and use it sometimes. I ought some specific injector cleaner on Mech's advice too... what the hell. The BlueDevil oil leak stuff worked and I never would have believed it. When the claims are modest, i am willing to try it, so as to prevent or repair something minor. My injectors are old. Perhaps they're a bit gunky. I think I'll treat them with techron and MMO for a good string of tanks, a few months worth. Can't hurt. Might save me a hassle.

Thanks for the advice re: coating the electrical grounds like that, Mech.

Sincerely,
James

[California98Civic]

Interestingly, once again, after maybe 200 miles "fixed" the exact same problem has returned: wildly leaning-out fuel trims, associated with a decrease in power, and decrease in fuel economy. My tank average is dropping fast. This is the third return after the initial repair. Each time the problem goes away for a few hundred miles, or even nearly 1000 miles, and then returns. First time I made it go away with a fuel pressure regulator, then replaced the regulator again when the problem came back, then fixed it by cleaning ground wires when it returned a second time. Now it is back again, for a third time.

Why does it run normally for so long and then return to this fail state again?

Puzzle!

[WD40]

Do you reset the ecm?
If you do it might take while for the cars issues to show up.

[California98Civic]

Originally Posted by WD40

Do you reset the ecm?
If you do it might take while for the cars issues to show up.

It's a good question. On the second repair with the pressure regulator, I did not reset the ECU (I left the battery connected) and the problem still went away. Then, another time, all I did was reset the ECU by disconnecting the battery for an hour or two. But that did not get rid of the problem for even a moment. When I cleaned the grounds, the ECU was of course reset.

Weird, huh?

[BabyDiesel]

I'm going to put money on it being the EVAP system. I have a P0446 code that took over 1000 miles to pop back up, and I had horrible idle and acceleration when it did. It was undrivable.

Might be an electrical connection for an EVAP component? That would explain it going out only every so often.

P.S. I am not a mechanic, so take my words with salt I can get my way around most vehicles though!

[California98Civic]

Thanks. MAP, Injectors, EVAP... there is my testing list. Maybe an intermittently open wire? But I can't see how changing a fuel pressure regulator or grounds cleaning would change the function of any of these components. Maybe there has always been three or so problem sorta layered on one another? Ugh.

But there has never been a CEL and the car does run, though not great.

[Chrysler kid]

Ok let's start over again

How many miles do you have on:
Distributor cap
Ignition rotor
Spark plugs
Spark plug wires

Have you tried to use carb cleaner around the intake manifold and hoses to check to see if the rpms change when sprayed on a certain part?

Have you cleaned the idle air control valve lately?
Is the coolant still fresh ?

Do you have any oil leaks around the valve cover

When is the last time you changed the air filter and inspected the throttle body for any dirt or build up


There was a Toyota echo 5 speed idling super low that just had tons of gunk built up on the throttle body the other day.

[California98Civic]

Originally Posted by Chrysler kid

Ok let's start over again

How many miles do you have on:
Distributor cap
Ignition rotor
Spark plugs
Spark plug wires

Have you tried to use carb cleaner around the intake manifold and hoses to check to see if the rpms change when sprayed on a certain part?

Have you cleaned the idle air control valve lately?
Is the coolant still fresh ?

Do you have any oil leaks around the valve cover

When is the last time you changed the air filter and inspected the throttle body for any dirt or build up


There was a Toyota echo 5 speed idling super low that just had tons of gunk built up on the throttle body the other day.

Here's another crazy deet: for the last two days the car has run quite normally, with longterm fuel trim moving to normal and then slightly rich. It has been raining these last two days.

Looking at your list, the cap, rotor, igniter, and spark plug wires have about 30,000, maybe. Maybe less. The plugs have been fuel fouled and cleaned. I have three sets that rotate in. No oil leaks. Compression is good. Filters are clean. I cleaned the throttle mechanism probably 20,000 miles ago, maybe a bit less. The carb cleaner would be for testing vacuum leaks, yes? I have not done that yet. I also have not cleaned the Idle Air Control Valve... both are good ideas.

[Chrysler kid]

Then the next question is have you checked your exhaust manifold for cracks? The car could be getting funny readings from the primary oxygen sensor if there is a Crack