Thanks Les and George, I'm going mainly off my idle in park and 2500 in park fuel trims as you said this was most important George. The engine definitely likes to run rich right now, which brings me to what you said Les. If the MAF was reading lower than expected wouldn't that mean more air is passing through than it's calculating, therefore causing a lean condition? And also, the engine runs definitely worse with the MAF unplugged, making me think the problem might be in one of the other sensors? Let me know what you guys think about that, or it's the fact my engine is already running rich, and in speed density it's programmed to run richer than usual causing it to run even more rich? Either way, I think I have nailed down a pattern here for the long crank time, guys I even caught it today. This was about 1 hour 45 min after shutting the engine off from driving home from work, it seems to always do this in the same situation, I will have to experiment more with this now but for now the video is below. Keep in mind guys, the engine will start with no problems with no prime on the first start of the day, the fuel pressure does not leak down at all. What could cause this long crank if not a fuel delivery issue?

 

Yes idle and 2500 for fuel trims. I was following up on the original discussion of fuel trims during a drive test that you presented where I was not sure at the time about moving through different fuel cells and LTFT’s.

Speed density needs rpm, IAT, MAP and possibly ECT and TPS.


George

 

Zach

I know that you and Les are exploring the MAF sensor and VE so I’ll let you guys work that through but have you convinced yourself that all the other sensors make “sense”? IAT, MAP, ECT, TPS, …?

What do you mean by “likes to run rich”?

When your truck has this long crank problem, will it start right away in clear flood mode with the pedal to the floor? The next time this happens open the throttle plate and see if you smell raw gas in the intake plenum. IOW, are hot injectors leaking into the plenum at rest causing a flooded hot start?

Have you checked cranking fuel pressure (opposite problem) when it won’t start? What about spark (ignition not fuel)?

Forgive me if I am covering established ground but this thread is getting really long and is finally exceeding my internal buffer. Lol


George

 

Thanks George, I have not convinced myself the sensor readings make sense. I was out looking over my lunch today with KOEO to see what all the sensors were reading, abs TPS - 0%, ECT - 45 C, IAT - 41 C, MAF - 0, MAP - 97.05 kPa. Guys, atmospheric pressure here is 101 kPa, could this difference in MAP reading make a difference? Here's the thing, I have read a MAP reading low would cause a lean condition, so unless it reads high under vacuum and low under no vacuum, this would not correlate to my rich condition at idle. I will look into this more as there is a discrepancy between the MAP and atmospheric pressure. Now, what do I mean by "likes to run rich". I mean the fuel trims are too high negative at idle in park (both long term over -10%), the exhaust pipe is covered with black, the exhaust makes my eyes water and smells very rich when I go back and smell it. However, it seems to run the most rich at idle, the fuel trims will clear up a lot while driving. So on post #32 George, I caught it doing a long crank time while I had the fuel pressure gauge hooked up, I was getting 50psi cranking and it would not start. I have not checked for spark at all yet, what would you check knowing the problem affects the whole engine, and also it doesn't misfire on any cylinders?

 

Couple of things regarding fuel trims.

he O2 sensors control the show. The computer has one objective: stoichiometry, an efficient cat and low emission. In a very few conditions this is abandoned such as a rich command at full throttle and a lean command at decelleration. The computer does its best to determine the appropriate fuel delivery while in open loop by looking at MAF/MAP/IAT/ECT... and going to a look up table supplied by factory programming. After the O2 sensors take over at closed loop the computer keeps looking up the theoretical fuel delivery and fuel trims are the difference between those theoretical values and the actual commanded fuel delivery. The newer the engine and with less problems then fuel trims are closer to zero. Older engines and/or engines with problems and the trims are bigger. So with 200,000 miles trims under +/-10 are considered OK, but lower is always more better to a point. You dont want perfection to be the enemy of the good. The question always is, if trims are too big, why is that and is the engine going to run OK anyhow? Depends.

If a global problem like a drifting/ageing/dirty MAF has occurred then the O2 sensors will catch that and apply their best take on stoich and all cylinders will get the needed global adjustment. To a point the engine will run OK. What happens however if one cylinder has a leaking injector sending a rich mixture down the exhaust pipe? That bank sensor says we need to reduce fuel delivery on this bank and the result is 3 cylinders running crappy. 2 are lean and one is probably still too rich or at least not firing right. There are other possibilities though.

Sensors can report the wrong values so they are the problem, including the O2 sensors. Oh crap the gate keeper may be wack. Wiring, voltages, computer, ... Is the computer correcting a rich condition or going inappropriately lean after a falsely reported a rich condition. Is it global or few cylinders. The truck might actually run better with one rich cylinder left alone instead of three cylinders with poor fuel control, except for the imminent death of the cat in that case.

Now you say you have black soot and gas smell so you probably are running rich but when and where? All the time or part of the time? Before or after the O2 sensors take over. Before or after negative trims. Does it run better better or worse in open loop at cold start up (no O2 sensors? Does it run better hot or cold? You already said that it runs worse with no MAF but do the trims change with no MAF? What do the plugs look like, are they all the same? Do they confirm a rich mixture?

That oughta do it for now.

George

 

Thanks George, I will go through all of these things you mentioned, eventually. I was an idiot today and was having too much fun on the trails in 2wd, kicked the tail out, and lost control right into a rock wall, she drove home after taking off the front bumper as it bent all of the mounts and was pushed up into the driver's tire, but it's home now and will get fixed. Guys I know I 'should' have been in 4x4, I know it was 100% my fault but I was having fun, my bad. Has some frame damage but I know it will drive again, I will post back on here when the blazer is all fixed up again. Sorry guys.

 

Doesn't look too bad! It will fix. I think that most of us has done something like this. Live and learn!

 

If you like some adventure in your life then your gonna bang a few things up. Look at all the new stuff your gonna learn how to do.


George

 

Thanks Les and George, so I got the Blazer all fixed up and back on the road now! A big thanks to Les for all of the help. I am now back diagnosing this rough idle, while I had the blazer all apart I noticed the MAF was very dirty, I took it out and cleaned it resulting in no difference. However, I found both donut gaskets between the manifold and exhaust pipe are leaking! I used an air compressor and soapy water to find the leaks. I replaced the donut gaskets yesterday and can still feel the driver's side one leaking! Do you guys have any suggestions to get a good seal? What do you guys think of high temp rtv or muffler cement? Here is a video of the leak and a picture of the blazer.

 

You're welcome! Good job! All looks great except for the paint, but you knew that! Just need some practice.

Maybe take exhaust loose on both sides and remount. Sometimes if you tighten one nut before the others, then things gets cocked a little bit. Make sure nothing is in between the two mating pieces. What are you doing to pressurinze that? Doesn't sound like the engine is running.