You have a lot of energy, I'll give you that. We are jumping around a lot here and we need to stick to a logical flow/process of elimination to find out what's wrong with your truck. If I ask about codes then that means that I have read your post and I am not clear regarding what you are communicating and need to understand everything that has happened so far before I can help you. As a fellow engineer I hope you can appreciate the value of a proper design of experiments and logical and complete attack on the problem. This is a great resource with some very smart and experienced Blazer enthusiasts but remember that you came to us and we are trying to help you.

The purpose of the fuel pressure test in this forum is to determine if the fuel pump can produce the minimum pressure when energized with KOEO and HOLD the pressure for a specified period of time with KOEO which tells us if there are any leaks. In rare cases the fuel system pressures are wonky enough to require monitoring during driving conditions but not usually. Please report the initial energized pressure and the pressure after the required hold time, all with KOEO.

I suggested to you that you do not fully understand your fuel trims yet and you reported that everything was unremarkable and dismissed my question. How did I know that we were not done here yet? A brand new truck does not run with 0% trims never mind a 20 year old truck with 100,000+ miles on it with "Duratrash" I think you called it, aftermarket replacement parts. It is statistically impossible for the fuel trims to be 0% across the board. Fuel trims are not the end all (although Les will be the first one to point out that I like using them) but in this case, they are very useful to find out what's going on. A number of things need to be cleared up here:

You have an older scanner and as such fuel trims were handled differently than with modern equipment. First integrator=short term fuel trim (STFT) and block learn= long tern fuel trim (LTFT). you operate with a scale from 0 - 255 with 128 being 0%, < 128 = negative fuel trims (computer subtracting fuel to compensate for a rich condition) and > 128 = positive fuel trims (computer adding fuel to compensate for a lean condition. Today we think of these values in percent deviation from the theoretical fuel delivery value for a given set of reported sensor values, or deviation from 128 in your case. An approximate translation is that 102 = -20% and 154 = +20%. In most vehicles +/-25% sets a code but the vehicle can have significant problems once the absolute value is greater than around 10. You always add the STFT and LTFT for a given bank being mindful of sign. When the truck is started cold the fuel system is in open loop, the O2 sensors are ignored and the PCM delivers the fuel injector pulses appropriate for the reported sensors which would equate to fuel trims of 0%. I don't know what the MT2500 reports during open loop. As soon as the engine reaches the appropriate temperature the system transitions to closed loop and the PCM starts reading the voltages from the O2 sensors and has the singular objective of minimum emissions accomplished by constantly varying the injector pulse width to keep the exhaust at the ideal air fuel ratio of 14.7:1. Then it looks at the fuel delivery that it has selected for ideal exhaust content and compares what the ideal data table driven values would be for the current set of reported sensor inputs (ECT, MAF, TPS, etc) and generates a deviation value. A complete analysis looks at the combined values for each bank at three rpms. In one set of trims you report STFTplus LTFT of +85% which is not unremarkable, as a matter of fact that is catastrophic. That is the highest value of fuel trim that I have ever seen reported. If fuel trims are out of bounds then there is either a fault that perturbs fuel delivery or air flow or a sensor(s) is reporting incorrectly or there is a wiring/connector problem or the PCM is hosed. Warm up the truck and generate STFT/Integrator and LTFT/block learn for each bank at three rpms (idle, 1500 and 2500) which is 12 values. If you have already done this then please summarize them and we can go from there.

If your not comfortable with my approach then I will drop out of this thread and let some of the other members take a shot at helping you. I take a technical engineering approach to these problems which irritates some and some guys prefer to guess the fault and replace parts. I prefer the former but we can spend your money and throw darts at some educated guesses if you want. If that's the drill then check your MAF wiring and connectors, replace the MAF, same with the o2 sensors and the ECT sensor.

Let us know.

George

 

George,

Thanks for your help and any you fell like adding, but you obviously could not/or chose not follow the data I have shared already on fuel trim, etc, and we are just talking past each other. And I am not in the habit of repeating data I posted in Post #1 and the last post on fuel trim. Post #1 fuel trim was before I cleared P0102 code. Fuel trim in my last post was after clearing the P0102 data. I for one am ready to suspect a faulty MAF, and hope it is not the PCM. I see no usual or unusual signs of wiring or connector or ground, etc issues. In fact the wiring and connectors all look almost new. It is very clean rig for 22 years old. Which is something I have a not experience tracking down (wiring/connector issues tracking with old school multi meters).

I assume from the lack of replies there is/are no static ohm tests for this MAF sensor to determine if it dead, and in DOA????

Is there anyone else here that has any contributions to offer at this point? Other than ask George?

Is there no one here that can understand the post #1 text and last posted fuel trim explanations I made? I am pretty sure they were quit clear, and in english?

Thanks for the fuel pressure link specs. Also please understand I am new at this either. I have ruled out any fuel problems 100%. It is down to a sensor problem now IMHO.

99.9% sure it is not wiring.

Does no one have a simple ohms test for the FSM? If not I will back probe and test it live.

 

 

Best wishes for your wife, been through a few surgeries my self, and near death issues last 4 years, its no fun. It also explains the missing what I said issues.

Take care of your family.

For other readers, more has happened. Earlier today it had an entire 24 hours with no codes, and lots of driving, stop and go and the fuel trims returned to normal (they were not going bonkers in a lift off rocket mode to infinity like a day ago that ended with the engine dying) when I tested it once it was good and hot today. In fact everything was looking normal (too many data sets to post details here) . Then the owner (friend I am helping...) headed home and the CEL started flashing. We have a new symptom!!! Do not know what codes it triggered yet. Will advise when I have that data. I already warned the owner what the flashing CEL means. "Do not risk driving it"!!! Danger Will Robinson!

It is now obvious that I am looking for a Blazing-Gremlin with a cloaking device, LOL. Last one of these I isolated was a real trickster. It was a failing shear pin that held the drive gear on my Distributor shaft on my 87 Renix Jeep. That was a fun one, LOLOL, JK.
Scanners, DVMs, Voodoo spells, Vacuum/Fuel gauge and on and on tests were useless, except to confirm what was not the problem. "These are not the droids you are looking" LOL

It acted like a possessed, sometimes, rig. Hit 290,000 miles on that rig, still runs great :-)

We tried wiggling everything we could reach on this Blazer, and never could trigger the problem. Leaning towards an over heating electronics part.

Maybe a few days before I have more data/updates. But what ever it is, it did not show any signs on any of the scanner data. ALL the engine operating data looked normal for about 20+ minutes today.

 

There are no magic and mystery involved. Just pure engineering. Same as George, I prefer to spend 80% of my work on accurate troubleshooting than replacing brainlessly things around and hoping it helps.

Best You can do now is to hook up the dongle permanently to OBD interface and drive around with live data on the screen. Then, if the problem occurs You have to notice the fuel trims. Personally I'd bet for the vacuum leak or fuel pressure. And, to be honest, I don't really understand Your stubbornness and not doing the fuel pressure tests like George advised.

As for the MAF sensor, here's the trace I've recorded some months ago with DSO:
There is no resistance check for MAF. The unit transmit pulses proportional to the air flow.
Mike

@George,sorry to hear on Your problems. I am crossing my fingers things will sort out good and the harsh time to be over as soon as possible.

 

I had a Chevy pickup in my shop several years ago.
On occasion hard starts with back kicks like timing was off, misses while running down the road ECT. Then every thing would be great for a while then back too the same old problems.
Timing chain fine, lower dist gears fine ECT.
After chasing codes and beating head on wall for a couple weeks I looked over the dist again and there was a small hair line crack in one of the pickup magnets.
Crack would close no problems, work its way open it gave extra signals,
Point is sometimes the reason why will just slap you in the face without warning and the only thing you can say is DAHH......

 

"@George,sorry to hear on Your problems. I am crossing my fingers things will sort out good and the harsh time to be over as soon as possible."

Thank you Mike. Getting old is not for the faint of heart.

George

 

You can sure say that again. I had been healthy and as solid rock for about 30 years since my late 20s, not even the flue ever got me, then I lost 80 lbs in 12 weeks fighting
a flue bug, virus, in bed, with severe bronchitis, Every muscle and joint in my body was on fire. Doctors missed the signs twice, gave me antibiotics. I finally figured it out, and found a specialist that confirmed the second problem, and we all still missed a 3rd and 4th problem. I sorted out of three of them, confirmed them and the doctors found the fourth after 5-? months. The cure and weight loss caused 2 more illnesses that led to 3 surgeries spanning 2 years. Long story, but I but I went from a healthy ox to not being able to lift a glass of water with just one hand, and not being able to sit up or stand up or walk with out help. It all started with a flue bug/cold. I really did not think I was going to live past 2014.

I did learn two things, many of today's surgeries are a cake walk compared to 50 years ago and Rx meds are two edged sword. They fix one problem and cause others.

 

Mike.308, thanks for the reply.

odat, many thanks!!! That is some, not all, but some of the kinds of answers I am looking for. What are some of the usual and unusual suspects. I have a history of working on stuff no one else could figure out, and solving it. What ever is going on in, is there one minute and gone the next. I have tried wiggling hoses and harnesses, but no joy there.

Last night my daughter pulled up with her 95 blazer, with a knocking noise. A mechanic had just changed the fuel filter and spark plugs and plug wires (cap and rotor was already new) to solve some sort of issue (I never got the story on that). Her husband was with her raising hell thinking she had let it run out of oil. In just a few minutes, with out even starting it yet, I noticed the primary wire on the Dizzy cap was loose, very loose. Then we did some more checking and found out the top of the radiator was cold...etc and basically the radiator was about 2/3 empty of coolant.

Never needed a scanner, over heating block caused the knocking. Not sure how a mechanic let them leave with the cooling so low on coolant. They knew it had a very small, slow radiator leak. Anyway, fired it up and it ran like a new engine.

Sight, smell, hearing and touch senses can supply a lot of empirical data no scanner can. Scanners are nearly useless on a non start engine. I learned how to debug 1987 Renix Fuel injection rigs with nothing but an old $300 analog multi meter ages ago. I now trouble shoot then online with nothing but empirical data first, and then if needed voltage/resistance tests, sometimes a vacuum gauge, fuel pressure gauge test added. We had no scanners for Renix rigs (we could afford) for 29 years.

What I can not understand is why no one so far has been able to read and understand my findings in the earlier posts, and offer any useful ideas except you just now?

Thank you very much for the info on the distributor pick up. I was already wondering if the CPS might have a heat failure issue, but the fuel trim data I have seen, that is normal in some tests, and goes bonkers after I clear the computer memory to force a relearn procedure, that causes the fuel trims, all four to run up from 128 to 160, and then immediately stalls the engine in say 2 minutes (at idle or at any other engine speed, or decel or acel). And then starts at 128 baseline seconds later on a restart, and repeats the cycle is puzzling so far. But then after say an hour of running and stop and go driving, the fuel trims, all four, barely move in park, or while driving, during rapid decel or rapid acceleration, and move in a Min-Max narrow range of 128-136 (128 is zero for folks not familiar with Snap-On MT-2500 tools) and still stalls out at idle or during acceleration after 2-3 minutes of the engine running (sometimes 5-10 minutes, it is random how long it runs before dying). It also does not seem to be engine temperature related (I thought it was earlier, but a day ago it was good and hot from a long drive on a hot day, and ran for 5-10 minutes at idle, etc with out dying). Since it can die just idling, or in park pressing the gas pedal, I have ruled out some possible problems. Also the scanner data on all the sensors, looks 100% normal, so far except the crazy fuel trim run ups after a computer re-boot/wipe... that later goes back to normal looking fuel trims.

I thought the wild rising fuel trims, after rebooting the computer, might be a solid clue, but not so sure now. The rig is across town for now, and It may be a few days before I can get any scan data for any new codes. But the flashing CEL tells me there may be fresh new clues now, as it had never flashed before according to the owner.

Thanks again, I will take a closer look at the Dizzy guts. We had not done that yet. I do have a new cap and rotor on order. It is well past its EOL date, LOL.

 

I take it fuel trim data did help help find, isolate and solve that problem?

:-)