Thanks Les, so I am not so sure of the fuel pump anymore lol. Haven't checked any plugs but it was definitely smelling a bit rich while I was sitting at home looking at the fuel trims. Could pull a plug tomorrow and check the condition. Another thing has come to mind here, so the extended crank has been mentioned on here also, it gave me another extended crank today right around the 1/4 point on the temp gauge (it always gives an extended crank at this temperature). It cranks for a good 5 seconds before starting up, then this is the same extended crank that it gives me on some mornings too. I was thinking tomorrow I want to see my fuel pressure when it starts up right away at operating temp then I will leave the gauge on and wait until it's at 1/4 on the temp gauge so it will give me a long crank and see again if there is any noticeable difference in what's going on. I'm thinking the basics air, fuel, and spark are needed to start so what's going on when it does this? About the sensors etc... Temp sensor I know is good as I always use the gauge on the dash lol, also saw it on the computer with the MAF (reading around 5 to low 5's g/s at idle) so that was all looking good. Another thing to note there, while I was out today I took a good note of how the engine acted when switching from open to closed loop, and there was no noticeable change. I know this contradicts my previous post but something just isn't adding up here. It's not misfiring on any cylinder, fuel trims are the same on each bank or always very close to each other. So whatever it is, it has to be affecting the whole engine, and I tested the fuel system today and saw great results. Maybe it's time I look at my ignition system for a second, hmmm. The whole system is brand new though excluding the ignition coil. Maybe if nothing shows on the little fuel pressure test above and the dead-end pump test I will repeat testing the ignition coil at 1/4 on the temp gauge.

 

Sounds like a reasonable plan. Best to catch it in the act of running poorly.

 

Thanks Les, so turns out the place I thought had the fittings doesn't have them either. So I won't be able to do the dead-end test for now. I just tested the coil and seemed good, was putting out a good 1" blue spark (video below). I took it for another spin to get it up to operating temp and noticed FT's only -5.5% at idle today, not -12.5%, but that's about all I had to note the rest was good. Am now waiting for it to cool off so I can test spark at the 1/4 temp. The reason I jumped to testing spark first is I was thinking all last night about it and it just seems more logical for my problem to be something other than the fuel system with the pressure test and trim data we have already. Will be looking at the fuel pressure more later today as stated in my previous post if the spark still looks strong when I test at 1/4 on the temp gauge. https://youtube.com/shorts/e9SQW3DP3xE?feature=share

 

Okay I believe I have something now, I took a little mid-day nap and thought about my findings lol. Anyways, at 1/4 on the temp gauge, I saw weird things happen twice while testing for spark, I was getting very irregular spark from the coil. I slowed the videos down a lot so I could really see when it was sparking vs engine noise from the cylinder cranking and every other time the sparking seemed in sync with the engine cranking (as I would expect), but then testing at 1/4 on the temp gauge resulted in very irregular sparking that wasn't in sync with the engine cranking for a second. As stated above I got this irregular sparking to happen twice, out of probably 5 times total. What do you think about this Les? The first video shows slowed-down footage of 2 tests, the first being a normal test and the second the problem test. The second video shows the problem test at full speed. https://youtube.com/shorts/KKQHxntHNjs?feature=share https://youtube.com/shorts/Ve9rdOjmfWg?feature=share

 

That's pretty interesting! Not sure exactly what it means though, with the coil building max voltage.

I wonder if you could rig a device so the spark jumps a much smaller gap (close to the coil) and the engine would run. Then video it when running poorly vs running good and slow that down.

What do you think?

 

Thanks Les, so your saying to connect the spark tester to the input side of the coil wire so it will run while I'm testing? I could try this yes, I think the hardest part would be getting the engine to run poorly in the time I have the tester hooked on it, but I could try and this would confirm a spark problem with the poor running as well. I would want to see when my fuel trims dip to -30% or around there what is the spark doing? Later last night I did the same spark test again to see if I could duplicate what I saw above, this time at the 1/4 temperature I seemed to be intermittently missing spark when I should have had it, it would not jump the gap, then I got a few sparks jumping the gap, then back to nothing. It was nice and dark out so the video should have picked up the spark arching elsewhere. I want to retry that test today at the same temperature and see what I get. It's making more sense to see a problem with the ignition system here, especially since I remember already testing fuel pressure for this extended crank issue a while back and found nothing. I also have tried priming the fuel pump many times before starting at this temperature and it would still give me an extended crank. I'm looking at 2 things here to be the culprit, the coil, or the control module, it seems viable for either to have a problem correlating with engine temperature as they both sit right on the engine. And I'm not so sure how I can pinpoint which one is causing the problem.

 

Holy smokes, I turned her on this morning and it did it finally! It was before making it into closed loop, it was running real rough and I was holding the rpm at about 1500 then let go to idle and it just stalled. When I started it back up it was running very bad and stalled on its own again (like what happened in the middle of the road), then started it up again after and it would hold steady rpm after letting off the throttle and seemed to be running good. Also to note is after it started normally again there was excess backfiring when I first revved it up a bit, then it wouldn't backfire anymore like normal. I think this would confirm the rich condition? https://youtube.com/shorts/baoeeSamWU0?feature=share

 

What code was set (the SES light was on). Also, my Blazer runs this way for a while after battery has been disconnected for a while.

Sorry but I'm not quite sold on the "runing rich" just yet. Still I have nothing more to offer other than pull the plugs and see if they are getting carboned up and/or pursue the SES light code.

 

Thanks Les, the only code was P0420 which has been there for a long time now. I pulled a plug and it looked fine, didn't look like it was running very rich. I also did the spark test again yesterday and found good constant spark when I tested. I then realized my IAC valve was making some funny noises so I took it out to inspect further and made the pintle and spring shoot out lol. I swapped in another one I have had, and its motor sounds much nicer. In the video below, the first valve is the original, second is the one I swapped in. So here's a little backstory on my experience with IAC valves, I had the original one in, then it was causing me a problem where the truck would not idle at all but run perfectly if I was on the throttle at all, then the next day with changing nothing it was able to idle normally again. So I still replaced the valve with an aftermarket one and never had any more problems like that, then I thought I was having some other problems with this aftermarket one so I swapped the original back in and have been running with the original for a few months now with "no issues". I'm thinking I have solved that stalling out-of-nowhere problem now... I was thinking about it and it seems to be almost the same thing where sometimes it will idle fine, then sometimes stall when letting off the gas, but runs well off idle. I also started it up 4 or 5 times yesterday at the certain temp (in different heat cycles) and it never gave me an extended crank. Fuel trims still look rich though. I also tested the primary and secondary windings of the coil yesterday and found both within spec (0.3 primary, 5750 secondary). Will be playing with it more today to see if it will give me an extended crank still or if I can get it to stall again. https://youtube.com/shorts/DaB8Em5dtGw?feature=share


I am leaning toward replacing the ICM here because of the inconsistent spark and persistent rich trims, I think ICM not coil because the coil looks great it can jump the 1" gap with no problem and the spark looks strong. Additionally, the resistance tests showed nothing on the coil, and all other system tests have resulted in good. If I still see problems after replacing the ICM I may look at replacing the coil, they are both the only ignition components that are still original, so I don't really have a problem replacing these for the reliability of my blazer. Especially with this big 12-hour trip coming up. On that note in the last few days while being around in the bay I noticed a very small coolant leak from the driver-side pump gasket, I think it's fair to say this is my fault, those damn gaskets are so hard to line up while the accessory brackets are still on with the alt and ac compressor up in your face! Thinking I will take this opportunity to swap out the thermostat for a fresh one as that's the only thing I haven't replaced in the cooling system thus far, I was also looking at some threads about the pump and I may try a thin layer of rtv on the pump when reinstalling so I can just stick the gasket to the pump and don't have to play around with dropping the gaskets again. Either do something like that or install studs in the block I'm thinking, the studs would be a little bit more involved task though.

 

I think you've done about all the diagnosis you will get done easily. So I think I agree that it warrants an ICM out of the parts cannon and see if that is it! Good luck getting it ready for the trip. Let us know.