p0171-174
 

Just replaced tank and fuel pump to fix a leak and trouble code for fuel tank pressure sensor on my '02 2dr 4X4 Blazer. After start up it missed and threw code for miss fire. We found we had 80 psi of fuel pressure. After we replaced the pressure regulator it runs fine except it gives me codes P0171 and P0174 which is a lean condition. I have check vacuum hoses and found nothing. What could we have done to cause these codes? HELP!!!!

What you did was reduce the pressure from 80 to 60. The poor wittle 'puter is confused. It tried to cope with higher pressure and shortened injector cycle.. now it has to adjust fuel trim back to longer cycles.

Disconnect battery cable for an hour or so, or overnight.. think that still works.

Disconnected the battery for about 4 hours. I was surprised to see the codes were still in there when I hooked it back up. I cleared the codes and made a couple trips with it and the MIL came back on but this time only the P0171 and P0171 pd codes showed up. I'm hoping that I'm gaining on it. I cleared the codes and put some Sea Foam in the tank to clean things up a bit. If that doesn't do it I'll disconnect the battery for a couple days and try it again. Thanks for the info.

Disconnected battery for 4 days, I don't think it did a thing. Still have same problem. Any ideas, anyone?

How's it running? If it's hesitant on throttle up and jerky, try disconnecting MAF connector after warm up. If it drives better, clean the MAF

Had battery disconnected for 4 days (I'm not sure this works now) and nothing changed. I did see on another thread where someone said something about the air box or duct on top of the throttle body might suck air where it meets the T/B. I sealed that area and am waiting to see what happens. It runs perfect, doesn't feel lean at all, just throws codes.

What is the idle rpm, warm? It should be 650 plus or minus 25, if it's higher than that, it's a vacuum leak on the engine side of throttle plate.
Test: Warm engine. Take off inlet tube at throttle plate, loosen IAC, slide thin feeler gauge over outer IAC port {filter side} and snug the iac bolts. If it then idles at 650 or more, you either have a vac leak or someone screwed with the throttle stop screw. Adjusting that screw is a last resort and will not affect the fuel air mix. The reason is that the IAC has to have a working range so the rpm with iac closed should be below 600.
But really.. whether or not have a vac leak, Just clean the MAF. And make sure all clamps between MAF and throttle body are tight. It's part of good maintenance, anyway.

It runs great. Idle is about 600 rpm and steady. No lean hesitation or roughness at all. If it wasn't for the codes showing up, I never know anything was wrong. Is it possible that the fuel filter could be bad and still show good pressure but loose volume? Sealing the air box didn't help at all. Took it for a short drive to warm it up and shut it off for a few minutes. Started it back up and within about a mile or two the MIL comes on with 171 & 174 showing up along with 171 & 174 pd. I will try cleaning the MAF also. I just don't understand how changing the tank, fuel pump, and pressure regulator could cause all this. I've got to get it E-checked in May and want it to be right.

Thanks again,

As far as being old, I'm only a couple years behind you.

OK, cleaned the MAF and replaced fuel filter, had absolutely no effect. What is left? I am thinking about TNT. Found MAP a little loose feeling. Removed it and used a small amount of silicone to seal it in hole. Today I tested it and it ran fine. First trip about a half hour and showed no codes. Second trip about half hour and no codes. Third trip in ten minutes MIL came on. Drove homeand checked codes. Had P0171, 174, 171pd, 174pd and P0137. It was also showing a tendency to run a little hotter than normal. I have cleaned the radiator and condenser so I know that's not the problem. It didn't start to get warmer until the MIL came on.

Well... this sorta stumps. because the only driveability issue you show is tendency to overheat, which too-lean does.
Check your ECT and IAT against this
Attachment 38428

Check MAP scan against manifold vac reading. Man vac should show 17-22 inhg. you may have to convert what MAP says.. remember it registers ABSOLUTE pressure so it's reading will reflect above pure vacuum.

Is there anything he could have done changing the pressure regulator that could cause this problem?
Thanks again.

If your FP now reads correct, I cant think of anything that would result in a perpetual lean.

Suggest you read your plugs. I imagine all would also indicate lean.
Longshot is that all or most injectors are crudded up.
If you're thinkking of upgrading to MPFI, now's good a time as any

Check those things above, first.

Don't I already have MPFI? Reference voltage and resistance on IAT seem to be good. I can't even find the ECT. My book says it's near impossible to get to. Yesterday I had over an hour of normal use before it started to screw up. I thought I had it whipped. Is there a way to lock it in open loop? Everything is fine in open loop.

I dont know if you have mpfi.. maybe.

Sure there is.. put in a resistor in place of ect to make VCM always think it's in warmup. of course your gas mileage tanks.
Here's the approp VCM conn with ect. You can measure there.

Ooops. no 5v on that conn. Find 5v pin on the iat or whatever and ohm from that to pin 23

Thanks fellow Buckeye. I've decided to bite the bullet and spend $50 on a diagnostic next Tuesday. They told me it takes 2-5 hrs to do. Maybe it will come back with something simple. What ever, I'll let you know.

Bit the bullet and had a diagnostic run and it came back "low fuel pressure". Said we only had 48psi running, so we are going to try another regulator since the pressure before was 80psi. I hope this does it.

What happened?

Don't trust after market pressure regulators. Stick with OEM. Everything seems fine now.

Don't trust after market pressure regulators. Stick with OEM. Everything seems fine now.