Hey everyone,

So a month ago I had a bunch of O2 sensor codes, and it turned out that after trying 3 times to replace with Bosch OEM O2 sensors, it was determined that the ECU was bad and not heating the upstream sensors. So after a new ECU that was fixed, and no more codes for a few weeks. Truck was running well and no issues. Just last week the truck begins a little bit of "coughing" after warm in traffic or at stop lights. Then the CEL comes on and codes P0171/P0174. I should back up and say that in addition to the 4 new O2 sensors, the truck was also given a FULL service in the fall...I literally replaced everything which also included the plugs and wires sparing no expense. So with new plugs and wires, as well as no vacuum leaks, I said the only thing it could be is the fuel pump or the MAF... I can clear the codes and right away they come back as "pending." So I went to go purchase a brand new MAF, and they didn't have Bosch, but did have a Delphi model in stock, and the guy told me they were a good company that makes a lot of OE parts.

Now my question...I put the new MAF last night, and right away the truck seems to run a little worse. I drove around town a little and CEL came back on. Pulled into a gas station and filled tank and added red line fuel system cleaner and disconnected the battery for 10 minutes. Got on the highway and tried some full open acceleration and while she ran good on the highway, back off the highway at stop lights still the "coughing." CEL hasn't come back on, but P0171/P0174 are still under the pending codes. I have a wifi OBDII with dash command, and fuel trim the LT is 25% but the ST is 1-3%...does the computer need time to learn the new MAF? Or is the MAF bad? Perhaps the fuel pump? But I know there are no vacuum leaks, and there are no intake or plenum leaks as when I put new lifters in the fall all new gaskets above the heads were replaced and everything torqued properly. No leaks at all (rare for a Disco ). I am wondering if I should return the Delphi MAF and just wait for the Bosch to come on order?

Any thoughts or advice would be GREATLY appreciated. I have put a lot of work into my Disco as she is my second and I love & plan on keeping her. She's a 2003 with 105k now (I got it with 89k). Replaced timing chain/sprockets - front cover (as I was in the VIN range), water pump, lifters (tapping), all gaskets except head gaskets (compression tests good), all new hoses & OEM gray warm climate thermostat, new 8mm silicone wires with bosch +4 plugs, and all fluids have been flushed and replaced with synthetic.

 

Well first, congratulations on all of the work you have done and, reading the list, I'm not sure I would have any better idea than you...

Do you know anyone else with a Disco II? Can you swap a known good working MAF in? Does your scanner show voltages for the o2 seniors? Honestly your troubles sound exactly like troubles I have had that were solved by MAF replacement and o2 sensors. I have gotten brand new bad ones of both, and went nuts thinking they can't possible be bad.

 

Have you tried unplugged the MAF? Unplug it and see if the idle smooths out.

 

A well-known, long time contributor here, who's no longer around, was always adamant about using only the correct Bosch MAF. He could never get anything else to work correctly.

As said previously, if you know anyone with a DII try swapping the MAF to see what happens. We did that with a friend's truck and eliminated the MAF as the cause of the P0171/P0174.

You say you checked for vacuum leaks, but in some cases the vac leaks have been traced to bad fuel injector o-rings that are sometimes difficult to locate with a smoke test.

 

I changed my injector o-rings and those codes cleared right up for me. There's a Ford part which switches right out if you don't want to wait on a set to be shipped in. I've posted it somewhere, you can probably find it somewhere in the link in my description.

I'm with the previously mentioned, well known, long time contributor here, who is no longer around (Disco Mike). The genuine Bosch MAF is the only way to go. I've tried several of the cheaper options and they simply don't work.

 

So AB has Three MAF's listed for the DII. I'm confused. Do the 4.0 and 4.6 share the same MAF? I would believe the 4.6 would want to see more air.

1. 99-02 Aftermarket Unit
2. 03-04 Aftermarket Unit
3. 99-04. Genuine

http://www.roverparts.com/nxt/?keywo...very+Series+II

 

The 4.0 and 4.6 share the same MAF, but the 4.6 has a larger MAF housing which the fuel maps are modified to account for.

 

What year is your truck?

 

Thanks for the ideas everyone. So I totally forgot to mention that my Disco is a 2003 with the 4.6L. I pulled the Delphi MAF out and took it back for a refund. Meanwhile I went and ordered the entire Bosch assembly...my friend has a 4.0 Disco and the diameter of the intake is different. But I have been reading and have read it's better to get the entire assembly as opposed to the lone MAF.

I am 99% sure the injectors are sealed properly. I cleaned and inspected them when I redid the gaskets.

By the way... Where did Disco Mike go? I have read a lot of his responses in old posts...

 

The assemblies are different but the MAF element is the same.