Well.. now it is setting code P0171 "with regularity."

I don't want to fire the Parts Cannon though it is tempting.

First step in diagnosis?

 

Google

 

Could just be the search function here... Or the tech article section where there is a list of conveniently posted trouble code diagnostic sheets. But an actual step by step diagnostic might actually find that things weren't fixed many threads ago...

Any bets on the topic of the next thread title?

 

It is so strange how the light goes off by itself!

Google reveals. Could be a clogged fuel filter,
A bad MAF,
A bad 02 sensor...

*edit: Well, I am researching it now. Although I am sure this is not "PROPER DIAGNOSTIC PROCEDURE," The first two things I did were:

1. Add generous amount of Redline SI-1 fuel cleaner to tank.
2. Use entire bottle of SeaFoam through brake booster, let sit about.. 20 to 30 minutes, then smoke out the neighborhood on warm (not hot) engine.

I immediately notice a smoother shut off. But I also did discover that the air cleaner connection to the MAF was loose . I also cleaned the MAF.

I will read a little bit, hoping others could share their experiences with this code. I also got P0174 once as well..

 

Seafoam... Isn't that the product that had a hand in your last engine demise? Probably not the common demoninator, but there sure is one, you can bet on that!

And that they have. There is a wealth of information on this forum waiting to be read. No need to wait pensively for others to rehash what they already posted about in the past.

 

So what are you trying to say. That *I* am the "common denominator?" No need to be coy or whatever, it leaves me guessing and thinking about things while i am at work and it ends up distracting me. I like it when people tell me exactly what they are thinking, instead of responses like Billy1820 putting up "Google" or generally implying that they don't need to help because they think they are replying to an idiot or wasting their time or something. It's not the biggest deal in the world.. anymore. I can tell you there was a time in my life where stuff on the Internet.. was.

Now I work 60 hours a week and while i am by no means trying to say that I work more or better than anyone else. First responders, like yourself, or anyone. That that is an achievement for me. And my 1 hour/70 mile commute to work - each way. For a round trip daily total of about 140 miles, 2 hours, at about 75MPH Garden State parkway, usually at 3AM yes I look for cops and sometimes do 70... to behave... is in the Blazer. Every two days it fills from a half tank until I run it down.

Your question about SEAFOAM, I should share that I at first used 100% water in De-carboning process. So. I learned what NOT to do. I secretly wanted to see what this engine could take as far as ABUSE anyways, given how in 2014 my 1st gen came to me with a Blown Head Gasket from the guy that used it muddin' - and blew head gasket. So, yes, SeaFoam I used at the end.. kind of like the mouthwash on the cavity.

But I get what you are saying, I hope I was able to share well.

I also did quickly Google and YouTube to do SOME research on the issue before posting. The whole "General information vs Specific to a Blazer" thing. Did not think it necessary to say, but, no problem. I do have a condition and okay fine.. even if nobody cares? Guess what, I still have it so. Assume I won't feel any type of way about what you have to say (I won't) and please always clearly tell me what's on your mind.

The RTFM posts.. I get it, okay, but I think the dialogue here is fine, nobody hates me, right?? I've seen what happens with THAT narrative, too. Plus, I have two more cars non-Blazer now, for those keeping track.. again, I work a lot and am an adult now, so, those Internet games *mean nothing to me* and i STILL use all forums . That i need to .

Let me now answer second part before work.

So. I did quickly use search function. As you said.

It seems I found one post in particular. The gentleman with 4 codes. One P0700 and three engine codes, P0171 and 0174 and another.

He suspected his EGR was stuck open and he too had rough take off from a light.

So. I SeaFoamed it GENTLY, ONE FULL CAN on a WARM NOT HOT engine and while i was going to let it sit one hour.. the day got in the way and that turned into 20 minutes. Revved like anything about 5 minutes had it in motion.. Again, I learned what NOT to do as I made the old engine ROD KNOCK using straight WATER and being a little more reckless. And even then. It took an engine hit from a day (HOURS) of speeding to get it to do that. I was impressed. Anyways. This time.. my engine was mostly clean, but, after about 3/4 can it DID "hit something" - maybe even in the EGR. I dont know but other threads suggest to "start there" before pulling an EGR to clean and test it - and I noticed immediately that my shut off was smoother. No shudder.

I also discovered that I did in fact have a vacuum leak where the air cleaner housing met the MAF.

I did clean the MAF as well.

I took it to work, tested the AC. It is working "better." Might be a little low on charge, might not be. Might have been a leak, might have been the accumulator.. might not have been. I will reply to that one later, but, I am doing that like my old Corolla.. which worked fine, but did have a leak and then stopped. I got that working too so.

I hope this serves as a good explanation to how maybe i solved it just by tightening the clamp at MAF and how i am doing better.

Thank you
in

 

So there goes my 5 cents worth of MAF's...

IMHO we should start this by giving the reader an idea of what we are talking.

P0171
This code is thrown by an OBDII vehicle and indicates a general "lean" condition. More specifically:

P0171 P=Powertrain 0171=Lean condition on bank #1

Troubleshooting guide here on the forum:
https://blazerforum.com/forum/diagno...plained-35154/

GENERAL PICTURE
On a V-engine it implies that condition has been detected by the O2 sensor located on the bank where cylinder #1 is. If there are two O2 sensors (one for each bank) it identifies the side this is happening, when the car/truck has only 1 O2 sensor before the CAT it's just this and it applies to the whole exhaust manifold (left & right) of the engine. The 1st gen Blazers are like that, only 1 O2 sensor after the Y-pipe in front of the CAT. This can give you some information for further troubleshooting.

But do not get too excited about the bank thingy, especially vacuum leaks can do funny stuff to the air intake. But it could also rule out some issues, or bring others into the equation. In the shop I sometimes help we had a Ferrari 360 where the right bank was rich in idle.
This car has two wideband O2 sensors, one in each bank's exhaust manifold, therefore we could define which side was off.

"ALL" the air introduced to the combustion chambers of an engine has to go through the MAF. If some air sneaks around it, it will mess up your fuel balance as the injection is introducing only the amount that the MAF "sees" go through. So, yes, any vacuum leak downstream of the MAF will cause a lean condition. Pretty much the same as with a good old carburetor. Check that troubleshooting guide on point (5).

This said, it is depending on how bad the vacuum leak is. This can cause other problems, such as intermittent CEL light and code as it may only be present at idle or it leaves the defined parameters only under certain driving conditions (cold start / hot start - light cruise - deceleration) It can be present only when some systems are activated (we don't know yet where the leak is) i.e. A/C on or when it purges the canister, with 4x4 engaged or any other vacuum that is switched.

Another issue is, that we ignore what the factory has programmed into the ECU for compensation of wear and tear of an engine. We don't know when it switches to O2 based fueling or goes into open loop. So we have to stick to either, the factory diagnostic manual or some basics. An the basics may be wrong because we have to make assumptions, if we cannot properly measure/diagnose.

How to go about these issues?
I would recommend a search and some reading to better understand the problem, then go about it methodically. Always consider that we are usually dealing with old, cars and have to do some preliminary checks.

The following is my way also around old cars to make sure I have not missed out on some very simple things and it will help troubleshoot further if we cannot solve the problem as we get very quickly to a known-good state of some of the causes of this error.

INFORMATION
There is no tool more powerful than the correct manual. Period!

Get the electrical wiring & diagnostic manual for your car. No Chilton or Haynes can replace that manual. Armed with the correct information troubleshooting is 1/10th as difficult as without.

OBDII READER
If the car is OBDII you will definitively need a good code and parameter reader for your Blazer. Again, there is nothing more powerful than the correct information.

MAF / HARDWARE
Consider this: The MAF is part of the emissions legal required sensors. The manufacturers are not interested in building bad hardware for these parts. About the same as safety relevant things. They hardly fail at all! Even after years it is unusual these parts fail. They can become compromised in some ways (dirt, abuse, mechanical defect) but until measured and found faulty I would not go and exchange a MAF, unless you can get by a free one to swap with a known good one for troubleshooting (i.e. measure the signal on your MAF, then the known-good one.)

This sensor is very sensitive and needs a couple of things to be able to fuel the engine correctly. First make sure you get the airflow right. Easy on a Blazer: air filter - hose - MAF - hose - throttle body - (maybe another hose) - cap - intake manifold. Then make sure the MAF is mounted the correct way! You guess - there is an arrow somewhere on the MAF's body which shows the correct air path. (You would be amazed that I have seen a MAF been put on the wrong way by a garage... true on a turbo engine with complicated air flow... but it happens.)

Then make sure it is the correct MAF for your car! No point in going any further if it is the wrong MAF. Wrong signal from the MAF - wrong fueling.

Also make sure nobody has tampered with the MAF. Some geniuses come up with the very bad ideas of removing the screens, cutting out parts of the MAF and so on. Then check if the MAF has been relocated because of some CAI or individual plumbing. You can wreak havoc with the signal of a MAF if improperly positioned after bends in the plumbing made worse by a missing screen inside the MAF. Even turning the MAF sideways more than allowed from the manufacturer can get you a wrong output.

SIGNAL - ELECTRICAL
Do you have a good battery and is it fully charged? You would be amazed how many problems can arise from a bad/discharged battery. It may lead to conditions where reference signals are below what they should be and give false readings. We usually hook up the cars we are testing to the battery charger to have them read around 14 Volts.

WIRING
Then the wiring to and from the sensor. So many defects that we have been tracing to broken wiring. Engine bays are special environments and electrically (correctly: electromagnetically) a noisy environment. Add the heat, vibration, ozone, hydrocarbons and you have an environment where wires break down, chafe, rub, break, get oxidation and get loose sometimes.

American engines from the 70s to the 2000s are an electrical wiring mess. Never have I seen so many loose wires in an engine bay, connectors and fuses spread over the car. This makes it cheap to add options. No need for an option to have a specific harness. And it works - so why not build it that way. But even this wiring is hardly left to chance. Especially on the engine itself. There is small details which go unnoticed by many and therefore are sometimes fixed in the wrong way. An example: The wiring to the CPS (crank position sensor) usually has a sleeve around the two or three wires to the sensor. The wiring is routed in a specific way, usually avoiding to run along ignition wires and tries to cross them at right angles. The sleeve is usually a silicone rubber to withstand the heat and an additional shielding inside against electromagnetic interference.
The manufacturer makes sure that his wiring is not causing any signal disruption, or can pick-up signals from i.e. the ignition wiring.

CONNECTORS
Now consider sensor outputs. Depending on the sensor it may read in the mV (millivolt 1/1000 V) to 50 V range. Connectors with corrosion (due to the resistance) can drop voltage by just a little bit. MAF's usually are in the range of 0.2 - 4 Volts. So any "distortion" of the signal messes up what the ECU "sees" from the sensor.

Now you get the idea of what happens if connectors are corroded. This is also true for the wiring crimped to the connectors pin. If the wire starts turning black at the crimping, it needs to be replaced. But to check this you need the correct tools to release the pins from weather-pack or metri-pack connectors without damage.

In conclusion to this, any re-wiring or repair for sensor inputs has to be done correctly, using the correct wire gauge, the correct connectors, using correct crimping techniques and assemble it correctly into a new connector. Flying wires, screwed connectors and such are a big: no, no.

SIGNAL
Does the sensor emit the correct signal? Most of the time we cannot diagnose this, as a normal person does not have the required hardware and/or software plus the skills to determine that. While most MAF's give you a voltage signal, some deliver a frequency (FORD AFAIK).
Can you measure it? Probably... if you are very, very good with wiring, you could splice T-connections into the 4 or 5 wires or 7 wires of a MAF. You could even get the male and female weatherpack or other connector the MAF has and build your own diagnostic plug. Then with a "good" digital multimeter you can measure voltage in, ground resistance, and output (signal) voltage. When it comes to frequency you will need an oscilloscope and these are very expensive tools. Consider this: I have treated myself to a digital multimeter for 800$ - a FLUKE 289 and I consider this an essential to have for modern car wirings.

If you cannot assess the MAF in this way, you have to make an assumption. If the engine is running fine with this MAF, except for the P0171 we may try to take it out of the equation. As some cars can run without the MAF connected we could unplug it. They revert to a speed density mode of injection using other inputs and sensors. (MAP, IAT, CT, TPS, O2) Sometimes this can yield some information if the MAF is doing something at all. (Depends if it is running better, worse or whatever changes.) But you have to read the manual to figure out if this is the case or not.

That means we need a more practical way for all users. Start by following all the wiring, make sure all the wires are where they should be. That the wires are not damaged. Check the wiring thoroughly! All around! I have seen wires looking totally fine but on the underside the insulation had been chafing against the cylinder head in one spot an intermittently grounded there.
Check that the connectors are not corroded, distorted by heat or show any sign of "abnormal" wear or are unpinned (pins that slide back and make no or just barely contact). That is pretty much the only thing that a normal person could do. Now we have the electrical part covered in a very basic way (integrity of the wiring). The next steps on the wiring would involve measuring and you do not want to go about this without the proper diagnostic manual.

O2 SENSOR
The O2 sensor can fail. Sometimes they do, and depending on the type this sensor will give you a CEL light. Could be intermittent i.e. only on cold starts (maybe the heating of the sensor is broken) or a steady condition. We keep it in the back of our minds.
Normally the ECU can do some testing on that and should give you a specific error if the O2 sensor is going bad or the heating circuit is faulty.

AIR FLOW / VACUUM
Now this is the next step. Does it pull air into the engine at any other place "after" the MAF? If yes, from where could that be...

Consider this: Every place downstream of the MAF which pulls air into the engine by-passes the MAF and screws up your fueling. Trouble is that depending on the strategies built in, the engine may compensate automatically for it i.e. by using the O2 signal for correction. This would show in the fuel trim that you can probably get from an OBDII reader. (This is the reason why so many of our knowledgeable people on the forum ask for these figures.)

Use any harmless means of checking for vacuum leaks. (Google search... ) Listen to it and by any means, do move the vacuum lines, tug at them, pull them, move them from side to side. Careful not to get entangled with any moving parts on your engine such as the fan, V-belts and such!
Check with a vacuum gauge and the engine shut down. How long does it hold a vacuum? Please do not pull an absolute vacuum. Couple psi below ambient is fair enough. You can hear the hissing better without the engine running and you see what the vacuum does. Check all the plastic bits. These are the culprit of vacuum leaks on old cars more than any other part. They crack, they break. Check the hoses and if they are brittle consider replacing with the correct material. You cannot replace a vacuum hose with any hose. They can collapse and cause all sorts of problems if you get the wrong hose.

How bad is the problem? It may be an indication on the size of the leak. Brake boosters have large vacuum hoses. A/C and other appliances less so, sensors have the smallest hoses. Blocking off some of the identified sources is a means of troubleshooting vacuum leaks. Be aware that our Blazers have several yards of vacuum lines running into the car's dashboard, to the transmission, front axle (4x4) and such. IMHO the best way is a vacuum pump and gauge. You can pull a vacuum and block off some ports or pinch vacuum lines i.e. to the vacuum reservoir for the front axle and A/C.

These problems and codes are quite a headache for many and from reading so many posts about this I'm not too sure troubleshooting works without the factory manuals. If, like in your case you can find something amiss and it cures the problem - great - solved!
It leaves you with the doubt. As we 1st gen's know, we have to live with that doubt. We have no codes to read and no insight into the ECU's in and outputs. So it is all deduction from the result we get from fixing something.

What could also cause this condition? A blocked injector, bad manifold gasket, misfire (yes it can cause a lean condition because you have no combustion or only part combustion). Especially the misfire is a tricky one. It will cause an O2 sensor to read "lean". It can be detected by measuring the exhaust gas composition (high HC) and or the CAT temperature if equipped with a thermocouple. BTW this is what the Ferrari 360 uses to protect the engine from any of these conditions. And is also the reason why nearly any CAT engine has misfire detection because it burns the CAT converter if unburnt fuel is injected.



I hope this explains a bit about the MAF's workings and how it relates to vacuum leaks and why we cannot just rely on one thing.