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Fuel Injector code P0172 'Too Rich'

29850 Views 11 Replies 6 Participants Last post by  Aaron Cake
Our VIN #148 (2000) has had four O2 sensors replaced under warranty.
In 2004 we footed the bill for yet another O2 sensor out of warranty.

Now this month we have a similar idle surging issue (200 - 2500 RPM with stalling, battery drained, engine light on), and took it to the shop. Shop says code # is P0172, which means 'fuel mixture too rich'. They want to replace the fuel injectors (three of them I presume) for $850.

We purchased this car to a) save the environment and b) save money. If we have $1,000 repair bills every year we cannot meet objective #2.

Service man says the fuel injectors need to be replaced -- so I ask this forum:

Why so many bad O2 sensors, and why now the fuel injectors?

Cannot the fuel injectors be flushed or somehow cleaned, rather than replaced?


Geoffrey Smith
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Wow, 4 O2 sensors. Where there reasons given for the replacement?

Obviously, something is seriously wrong. You need to check/do the following:

1. Have the injectors cleaned. Many communities have shops that specialize in this. Check the Yellow Pages for "injection service" or "diesel service". Many diesel injection places have gas injector rigs as well. Cost is usually around $20 per injector. Generally, this is done ultrasonically and you get a nice printout with spray pattern, flow rates, etc. You will need to remove the injectors and drop them off.

2. Check fuel pressure. Proper pressures and proceedures are located in the service manual.

3. As mentioned, make sure the ECM recall is done. The recall addresses an issue that causes the car to throw LAF/O2 related codes.

If the car really is running rich, then you run the risk of damaging the cats, a very expensive problem. So this should be taken care of as soon as possible.

As an aside, the "technicians" in your service department CLEARLY don't have much in the way of troubleshooting skills past "replace the part indicated by the code". This seems to be a common trait among Honda dealers.
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geoffreyhawk said:
In 2004 O2 was replaced by Poway Honda, out of warranty. They said the previous 'bad O2' codes were mis-reported due to faulty ECM. This report (sorry don't have the code handy) is 'for sure'.
That's actually correct. The code in the ECM used to be too strict about the values it expects from the LAF sensor. The result was that the ECM would decide the LAF sensor output was "out of range" way too early.

May 2005, idle surging, drained batt, engine light on, took to Cush Honda in Escondido (all three shops have been dealers). He wants to replace injectors for $850. (Also replace a rat-chewed a/c wire for $350.)
DO NOT REPLACE injectors. :) Have them cleaned first. If that doesn't do it, then DON'T buy "Honda" injectors. Almost all injectors are made by only a few companies. I believe that ours are Nippondenso. Buying them from a Denso dealer will result in a SIGNIFICANT savings (like over $500).

Which battery was drained?

Prior to this latest malady, have had no idle problems, no auto-stop stalls, no cold running problems. Clutch seems to be going -- it lurches at cruising speeds, sort of like 'slack' gear, just between coast and acceleration it often lurches.
That sounds like the classis EGR problem.
Yes, EGR = Exhaust Gas Recirculation. It has been determined that a dirty/sticking EGR valve can cause the symptoms you describe (rough cruising, lurching, etc.). Unequal/unpredictable EGR flow causes combustion problems. Usually, cleaning the valve solves the problem. Sometimes, the entire passage must be cleaned, which means pulling the intake manifold to get at the EGR plate.
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