Alright, I know there are some previous posts regarding P0172 errors (system too rich) with first gen fits on this forum. I've read a handful of them. Still trying to narrow down what's up with it before taking it to the shop. My fit has 191K on the clock and just had a pretty good engine overhaul (all new seals, head gasket, studs, engine mounts, clutch, remanufactured injectors, O2 sensors, ignition coils and plugs). My dad and I are building it up to be a Lemons racer, so no power modifications, just preventative maintenance to go racing at this point. Things I haven't touched: the MAP sensor. I just swapped out the K&N air filter that the car came with when we bought it with an AC Delco standard filter from RockAuto. I'm going to continue to do my research and read up on the issue, but I thought I'd post here to listen to other's ideas or thoughts. Maybe things I can test to figure out what could be the problem since we basically replaced everything. I do have a live-data reading OBDII reader/diagnostic tool (the $100 one, not the professional few hundred dollar one though - so it can't do everything).

Thanks in advance,
Matt

 

As an update to this and hopefully a bump as well... I replaced the MAP sensor today with one from RockAuto. Didn't seem to solve the P0172 error code as 35 miles later, the CEL came back on.

Anyone have any thoughts on this before I end up taking it to a mechanic and having them troubleshoot it?

Thanks in advance!

 

I'm coming into this a bit late, but a P0172 usually indicates a leak in a vacuum line, air intake, or intake manifold gasket. If you have access to a smoke generator (yeah, fat chance), you can inject smoke into the intake and look for smoke escaping. If your OBD tool has a way to monitor the short-term fuel trim (I have a cheap-o bluetooth OBD reader + the Torque app to do this), then carefully using an unlit propane torch to inject propane around areas you might have a vacuum leak while watching the short-term fuel trim for a sudden swing would be another option.

 

I'm going to add to this in hopes of finding a solution...

It's been several months and this issue is still not resolved. The fit has turned into a track/AutoX car and isn't driven all that much on the street. Maybe 100 miles a month or so. Mostly hard driving on tracks and autoX days. A few weeks back we drove the fit at an warm(er) autoX event. We entered the car with 4 drivers (yes, you read that correctly - 2 drivers per heat). After the first heat, the car was good. 10 successive runs with hardly a sweat. 2nd heat was pretty much the same, but halfway through one of the last runs, the engine went into limp mode and capped us at 3000 rpm. We got it back to our paddock area and turned the car off, unhooked the negative battery terminal for a few minutes and fired it back up without issue. It drove a few more runs and then the same limp mode issue happened again. We ended up calling it after that, letting the car cool day as it was about 75 F and sunny. I drove the car home about 15 miles without issue going regular road speeds. The dash kept giving a P0108 - MAP sensor pressure too high - after the initial failure.

A week later I had a track weekend. First two 20-minute sessions went well. 3rd one went well too, but literally as I pulled back in to park and let the car cool down, it went into limp mode. From there things got worse. The P0108 CEL came back so I started troubleshooting. Ended up going to O'Reilly's and picking up a brand new MAP sensor that didn't solve anything. Eventually just driving around the paddock at the track the CEL started flashing indicating a misfire. Sure enough, cylinder 1 was missing (P0301 error). I swapped plugs on cyl. 1 and 2, that didn't work. I swapped coils on 1 and 2 and that didn't work. I ended up trying to swap fuel injectors on 1 and 2, but cylinder 1's injector came out in 2 pieces. So, I trailered the car home. Even starting it up and letting it idle sounded like it was only running on 3 cylinders. My guess was that the remanufactured fuel injectors I got from RockAuto weren't up to the task of hard driving on a track and gave up. Or they could have been bad from the start and were causing the P0172 error and the subsequent errors just stemmed from that. Needless to say, I needed new fuel injectors. The local Honda dealer was going to charge me $279 per injector. Since that's practically theft I skipped them and put in the injectors from a spare K20A3 engine I have waiting for the fit. Car fired right up, running on all 4 cylinders. Took a few minutes to relearn the idle, but it eventually held steady at 750 rpm. STFT's were obviously backed-off around -32% which is understandable. However, after about 30 more miles on the road, the CEL came back on for what I assume is a P0172 error again (I still have to confirm).

I'm at a loss if this is indeed the same issue arising still. Here's what I know:
- The car has about 192k miles on it, primarily commuter driven from Jersey to Manhattan from '07 till last year.
- The previous owner sold it because he didn't check the spark plugs and it blew one taking the threads with it.
- My dad and I picked up a "new" head from a junkyard with 20k miles on it (it was in great shape), replaced the head gasket, head bolts, clutch, engine mounts and various other gaskets that come with a head gasket kit (intake, exhaust, valve cover, etc).
- I originally did a valve adjustment on the new head and got valve tick. I redid the job and got rid of the valve tick using the high-side-of-the-clearance-spec-wont-slide-though-but-the-low-side-will method (if that makes sense).
- We replaced the fuel injectors with remanufactured ones from RockAuto since the original ones were cooked.
- Ever since the engine went back in, we've had P0172 CEL's every 30-50 miles once I delete the code.
- I've tried 3 different MAP sensors now; the original, a $15 one from RA and a $95 from O'Reilly's. Doesn't seem to matter.
- I've tried 2 different air filters. Those don't seem to matter either.
- We have a DCA header installed, but it has new O2 sensor (both up and down) installed as well. The exhaust manifold heat shielding was discarded because there wasn't a place to mount it. I'd like to think the heat radiating up in the back of the engine bay caused high intake pressures, but I removed the brake reservoir trim/cowl piece to vent heat and even after the car was cooled down, the issues still persisted.
- We have a K&N air filter, but the intake is totally stock at this point.
- I've checked for intake leaks post MAP sensor dozens of times and the only real places air could get in is the plenum-to-manifold gasket, intake-to-head gasket, brake booster vacuum hose and fuel injector ports. All are fine and correctly torqued down.
- The car currently has 310cc RSX type S fuel injectors.
- We replaced the Hitachi ignition coils and plugs with Denso IK22 iridium spark plugs. Both now about 1000 miles on them.

What am I missing here?

 

Sure acts like a vacuum leak. Have you tried using a smoke machine (home grown or commercial) to try to trace it down? Doesn't take much of a crack in a hose to cause a P0108. I assume if get that vacuum leak fixed, you'll have fixed the P0172 en passant. If you can't rig a smoke machine, the ol' mechanics trick of using an unlit propane torch around suspect area can also be used, but it's not my fave.

 

No, haven't used a smoke machine. I do have a propane torch though. I'll give that a try tomorrow.

 

Any recommendations on where to check first? Perhaps common vacuum leak areas in Fits?

 

Would a knock sensor cause a P0172 CEL? When we put our engine back together, the wire was pulled out of the female plug connector. We superglued the wire back into the connector and it never seemed to have any issues (no knock sensor codes thrown). But today I noticed that wire had backed itself out again. Would that have caused all the previously mentioned errors?

Update: I bought a new female plug connector and fixed the wiring to the knock sensor. Ran an autoX event today and the check engine light came back on. Same P0172 error code. Doesn't look like that was the culprit.

 

Ok. Performed a pretty MacGyver-ish smoke test. Weed sprayer with a hose into a glass jar with carboard chunks on fire. Had a second hose leaving the jar that slid into the disconnected (from the booster, not valve cover) brake booster vacuum hose. Removed the intake and sealed off the throttle body with a ziploc bag and a rubber band. Key in the ignition in the RUN position and got a faint wif of smoke out of the EGR valve. While I have replaced both serviceable gaskets for the EGR valve during our engine rebuild, we didn't test the EGR valve itself. I have a new EGR valve on order with gasket. We're going to perform the smoke test again after the part replacement to confirm the leaks have been fixed. Then I guess we'll be driving it for awhile to see if the check engine light comes back on.

 

Thanks for the updates!

So there's a vacuum leak in the EGR valve itself? Seems weird, there's really just the valve stem that goes through a very tight opening in it, doesn't seem like there's anywhere for it to leak noticeably. Have you tried just blocking off the EGR system completely? BTW I run it without a gasket at all and it isn't causing any issues so far lol.

 

yeah, the leak was definitely coming from the component and not the gasket itself. The car has 190k miles on it and virtually every part is original. I think with the new track use, it’s causing the original components to fail. I took the opportunity and cleaned out all the carbon deposits when the EGR was off.

considering that the gasket only costs a couple bucks and it’s super accessible, I’ll keep running with the gasket.

 

What area did it came from?

 

P0172 indicates rich mixture, plus vacuum leak on MAP sensor only engine will cause idle surge or higher than normal RPMs

 

Around A.

I just installed the new valve today. Initially threw a P0113 code (IAT too high - weird because it's only 67 F outside) and a P0172 code (fuel system too rich - from before). I cleared both and let the car relearn the idle. After about 5 minutes, it was hovering around 750 rpm again. Sadly, that's all I had time for this evening. I'll be doing further testing this weekend. Basically just putting on miles to see if the code comes back.

 

I took apart some valves on the wrecking yard.
The stem is passing trough the bushing and goes into the solenoid part of the valve.
Vacuum leak on the MAP equipped engine causes higher than normal RPM and not a lean condition.
Just for kicks I sprayed TB cleaner at area A around valve stem bushing in my car, but noticed no RPM change
If the valve replacement did not help, check the exhaust valve clearance , one or two tight valves can cause that (Honda Pilot)
Edited: smoke leaking EGR thread
https://www.odyclub.com/threads/smok...normal.355257/

 

that’s an interesting find. I’d think that the rise in RPM would actually be due to the ECU correcting for the additional air flow and adding more fuel. If the leak wasn’t that bad, then the fuel added could be too much and you’d get rich burn conditions. I’ll see what I find this weekend.

regarding idle speed, I’ve almost exclusively gotten idle speeds around 750 +/- 25 rpm. I’ve also adjusted the valves twice now (first time I didn’t do a great job and got some bad valve tick). 2nd time round resulted in better adjustments but still the code. So, I don’t think it’s valve related.

 

Welp, new EGR valve and the same P0172 CEL came back on within 30 miles. Vacuum leak solved, CEL not solved.

Looks like the Long-term fuel trim is around -21.9%. My car has the original CAT on it with 193k miles. Could the cat just be shot and causing the rear O2 sensor to throw the CEL?

 

I'm going to try the cheap fix to try and fool the downstream O2 sensor by adding a spark plug non-fouler in between the O2 bung and sensor. Will update when results come in.

Update: CEL came back on about 45 miles later for the same P0172 error code. Looked like the LTFT was -21.9% again.

 

I've been chasing mild (no codes) negative fuel trims on my GD1 as well...I think there are only a few possible root causes. Vacuum leaks shouldn't affect fuel trims on a speed-density system, AIUI, but you might see a high idle speed. Have you checked the evap purge valve and the fuel pressure?

 

...and are your coolant and intake air temperature and MAP readings reasonable?