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Discussion Starter #1
My Disco 2 has been running rich for the last 8 months or so. It always trips fault codes for both of the front O2 sensors and occasionally throws a "running lean" code

I can get the numbers for the codes if I need to

I've replaced the front two O2 sensors twice, and the rear two once, checked their wiring harnesses (just replaced both head gaskets), replaced the fuel pump, and thoroughly checked my fuses, even replacing a few that tested good but looked bad

It currently gets anywhere from 6 to 10 mpg and it's bleeding me dry

Any help would be much appreciated

Thanks,
Christopher
 

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I can get the numbers for the codes if I need to

I've replaced the front two O2 sensors twice, and the rear two once, checked their wiring harnesses (just replaced both head gaskets), replaced the fuel pump, and thoroughly checked my fuses, even replacing a few that tested good but looked bad
What are the numbers for the codes you are getting Christopher?

Also, do you smell fuel? How many miles now and when was the last time you rebuilt your injectors?
 

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I got 10.88mpg on my last tank ('99 DII) and that tracks usual mileage in town. But 6mpg is out of spec. Would help if you would clear all codes, let them come back, and then report codes.
 

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Discussion Starter #4
The codes are: P0171 P0174 P0150 and P0130
They reappear without fail about 2 to 4 miles after clearing

I have not rebuilt the fuel injectors since I have had the car (last 3 years), and they seemed to be original and undisturbed when I replaced my head gaskets about a month and a half ago


It likes to hang out around 8 mpg but fluctuates up and down based on factors unknown to me

Keeping in mind that it is nearly 20 years old now, I keep a Voyager roof rack on it, a 2-inch lift, and larger tires I expect the fuel economy to be a few miles lower than stock, but not this bad

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I take all of my mileage calculations over the same 44-mile commute
I reset the odometer each time I gas up to a full tank, and then divide my miles traveled by the number of gallons it takes to refuel

I also have 32-inch tires on my vehicle and have never had my odometer adjusted so I account for their increased size by multiplying the miles my odometer reports
by the ratio between the circumference of my new tires and the stock tire size of 29 inches (~1.103448)


i.e. If my odometer said I drove 40 miles and I had to put 5 1/2 gallons in I would calculate it as: (40* 1.103448) / 5.5 =~ 8


I also double check my distances with google maps

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If you think I've overlooked something or see something wrong with the way that I am calculating my distance traveled please let me know


I really appreciate the help, Im at my wit's end,
Christopher
 

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I would not try to figure out fuel mileage until you can get the codes dealt with.
All codes are lean and O2 related. Likely either bad O2s or vacuum leak???
You mentioned you just did head gaskets, what’s the story on that? O2 sensors previous to that repair? What brand O2 sensors?
 

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Discussion Starter #6
My car threw the four codes I listed (along with codes for the two rear O2s) just as it began running rich about 8 months ago, and after throwing many parts at it I replaced the four O2s with
the first set I got about 5 months ago

The rear two took and those codes have never resurfaced, however the front two thew codes several days after
This was before I had fixed my multiple oil leaks, and I found my front two O2 connectors to be soaked in oil

I cleaned these thoroughly with break-clean and contact cleaner and wished the problem away, but they continued to throw codes

This led me to replace the front two sensors again (with the cheap sensors) about a month ago worrying that the oil had somehow destroyed the first set

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I can't tell you what brand the first O2 sensors were because my dad got them for me as a gift, but they were most likely very cheap
The second set I got was also the cheapest I could find, I bought them because I wanted to get some that would at least work for a while
(even if they were poor quality) so that I could eliminate them as a problem without making a significant investment

I reasoned that I could upgrade them when they stopped working if that was the case

If I need to buy more expensive sensors from Atlantic British or elsewhere let me know, money is tight but I'll do whatever I need to do to solve this problem

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I have suspected a vacuum leak but have no experience dealing with them and do not know how to go about detecting one

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I replaced the head gaskets because I had my front cover gasket blow while on was on the commute that I mentioned before and quickly redlined my engine,
after replacing the front cover gasket I misdiagnosed a blown head gasket so I went through with that repair

In the process, I found multiple sources of my everpresent oil leak: rear seal over pushrod area, oil pan gasket disintegrating, valve cover gaskets leaking


This running rich problem was present long before this repair and I made sure to closely examine the wiring harness and anything else I could think of, yet found no damage

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Also, to respond to masantschi: Yes I can smell fuel when I run the car and my exhaust pipe is black
 

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There’s many posts and threads about cheap O2 sensors and the grief they can cause.
02 sensors can easily become contaminated by engine problems, coolant, oil, cleaning chemicals, even improper sealants and adhesives can contaminate them.
When in the timeline did you overheat the engine and do head gaskets etc. ???
If you have been driving it with these issues and codes for 8months? Catalyst damage is likely 😐
 

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Discussion Starter #8
I have been worried about the damage this problem might cause, but I'd be
happy to get off with replacing the Cats if that's what you mean by Catalyst damage

I have driven it just over 10,000 miles in this condition blindly throwing many parts at it along the way,
so I'm very happy to have a chance to hear from people who are familiar with this problem


I have attached a timeline of the relevant repairs


Thanks again for all the help and speedy responses
 

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I agree, I definitely need to fix this problem before I go about making any accessory repairs
I'd stop driving that truck till you get this figured out - you clog up those cats and OEM O2 sensor cost will be the last of your concerns.

As has been pointed out, we cannot use the cheap O2 Sensors. You need to get those replaced. The OE high cost have a warranty so if you have an issue within 12 mos or so, they'll replace them w/o issue. The reason your [rear] codes went away after you replaced the rear is because all that black stuff is clogging up your cats right now and it's not really getting to them, but rest assured, in your current condition, they'll start throwing again as soon as that carbon starts to fully work its way through and coat them - i.e. without fixing the underlying issue, it'll come back.

I think these two are your culprits, but I can be wrong...
P0130 - O2 Specific though it can be caused by Faulty Fuel injectors or inappropriate fuel pressure
P0150 - Fuel Rail/System Pressure is too high.

That said, I would perform a fuel pressure test. You need to hook up a fuel PSI tester to your line when it's cold and check your pressure (write it down). Then, you need to do the same with the key in the on position (fuel pump comes on) and then again after you turn the truck over and start it up. Report back your numbers, unless you know how to diagnose the injectors/filter/regulator or pump from there.

P0171 & P0174 together usually indicate you have a vacuum leak in the intake system. Since you just got the HG done, it's possible there was a step missed or something didn't get tightened down to spec or maybe a gasket is pinched or something? It's also possible that due to your fuel issue above, this could be a bi-product, since all these codes are coming back as fuel/air. Personally, I'd fix the above first and then perform the following if these are still present...

Begin by looking for a vacuum leak. With the engine running, spray some carb-cleaner around your intake plenum and heads, etc. to see if you get a reaction from your motor (you'll know it if/when it happens). If you hear your motor bog a little then you will need to focus in that area to find the leak. If that comes back clean, you need to perform a smoke test on your intake manifold. You have 3 options here - (a) Have a shop run the test for you, (b) you can rent a tester and perform the test yourself, (c) buy a cigar and get some plastic/rubber-bands so you cap off your intake and perform the test this way (I did c on mine).

Just my .02... hope it helps some
 

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Discussion Starter #12
Thank you so much for this advice, I'll order some good sensors as soon as I can and park the car until I fix the problem

1. Do I hook up the PSI tester near the fuel pump or the fuel rail or somewhere else?

2. I'll get back to you with my results once I've done the fuel pressure test

3. No, there is next to no chance that I pinched anything from the wiring harness during the HG repair, and I marked every bolt head with silver sharpie to ensure I torqued each one appropriately
I also had someone with me throughout the entire repair to double check everything that I did

Again, I'm very grateful for the advice, It has been difficult for me to find anyone who has dealt with a problem like this
 

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1. Do I hook up the PSI tester near the fuel pump or the fuel rail or somewhere else?

2. I'll get back to you with my results once I've done the fuel pressure test

3. No, there is next to no chance that I pinched anything from the wiring harness during the HG repair, and I marked every bolt head with silver sharpie to ensure I torqued each one appropriately I also had someone with me throughout the entire repair to double check everything that I did

Again, I'm very grateful for the advice, It has been difficult for me to find anyone who has dealt with a problem like this
1 - You hook up the PSI tester to the fuel rail. It's a {explicit} to get to because it's up against the firewall, behind the plenum, almost dead center of the LH Intake Side.

3 - I didn't mention the wiring harness being pinched - I was talking about gaskets etc. I'd still work on the fuel issue first, personally. It could clear up all your problems once fixed, and you get some Bosch O2 Sensors.
 

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If you are buying cheap O2 sensors, how are you connecting them to the car. You should not solder any wires as it will cause false readings.
 

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DII owners have reported problems with Bosch sensors too, including out of the box, including me. Several owners have reported better results with Walker sensors.
 

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Discussion Starter #16
1. Thank you for the info on how to do the fuel pressure test

2. Sorry for the misinterpretation, I will double check the gaskets to make sure I have not pinched anything

3. The sensors I purchased came with the appropriate connectors, so I didn't need to do any soldering

3. Id like to get a good consensus on the brand of sensors I should buy before I purchase them, also where can I find OEM sensors?


Thanks again
 

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1. Thank you for the info on how to do the fuel pressure test

2. Sorry for the misinterpretation, I will double check the gaskets to make sure I have not pinched anything

3. The sensors I purchased came with the appropriate connectors, so I didn't need to do any soldering

3. Id like to get a good consensus on the brand of sensors I should buy before I purchase them, also where can I find OEM sensors?


Thanks again
Honestly, as long as you buy decent OEM Sensors then so be it? I swear by Bosch but as Red said, he's had problems with his out of the box, and so he goes with Walkers. In the end, this is one of those items you get what you pay for and of the few items on my vehicle where I splurge, this is one of them. The last time I bought Bosch OEM Sensors (x4 new ones about a month ago for the E36), I found my lowest price online and then went to Autozone with the P/N and that price. They price matched it and I was out the door. This could get you out the door for relatively cheap with a set of Walkers...

For you consensus:
I use Bosch in my BMWs & Rover, and NGK in my Rubicon.

There are also plenty of threads on the forum where you can look up the +/- of each and decide which you want to go with. If my truck had Walkers on it when I bought it, I probably would have just stuck with those because I'm superstitious that way. I just wouldn't use something that someone reported did OK once upon a time?
 

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Discussion Starter #19
Problem Solved!

I bought and installed a set of Bosch O2 sensors.

I am no longer running rich, and I am now getting about 12 to 13 mpg.

The check engine light remains off after a month, and my truck is running better than ever!


Thank you all for the information and guidance, I would likely still be throwing the wrench without it
 

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Same problem as the OP same setup except:

1) I removed the cats and replaced them with fake cats
2) Front 02 sensors are Bosch. Rear 02 sensors are Walkers.
3) No codes

I'm getting 5-6 MPG maybe less.

No clue why.
 
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