109 g/s

 

That is considerably low. Are you getting physical full tnrottle with pedal on the floor? Can throttle body be opened any more when someone holds pedal on the floor?

 

Yeah. Throttle is at a near perfect 90 degrees with the pedal all the way down with the additional padding of my rubber floor mats.



Bad MAF sensor? I don't see how considering it's new. Maybe this Walker MAF sensor is defective? I can put the factory OEM one back in and test again.

Air filter too thick? I've been buying the FRAM filters for this model.

Just to be clear, this is the air intake configuration I have. It's the air box with the intake hole right behind the left headlight. No visible obstruction at all. Could it be this design is inadequate? I don't see why if 130+ g/s is expected at sudden wide open throttle.



Could it be excessive back pressure? Would that prevent expected MAF numbers? This question circles back to the thread I started about testing back pressure. Maybe I wasn't testing it right and there actually is excessive back pressure.

 

Excessive back pressure would definitely prohibit breathing well. If original Maf sensor is also low, then probably MAF sensor is Ok and there is another reason for it. That stock air cleaner box is just fine. But it has a little duct that goes through the radiator support that can get bent shut when misplaced. I did this to mine once.

 

So do the static and running compression tests as described (complete) and report. Then we can determine definitively from this if exhaust is restricted as well as general engine health. Yes I know it will be a pain! But Its just labor not $$$.

 

To LesMeyer: I'm extremely impressed with your knowledge of these Blazers. Could you possibly look at the thread "what should I do next" and give me your thoughts?

 

So how did things work out?

 

I've been away from this thread for a while because I decided to pull out the big guns and seek out a pro who knows a lot more than I do.

A while back before I started looking into this timing/misfire/low power issue I came across another YouTube mechanic that goes by Rainman Ray who seems really good an knowledgeable. He works at a shop called PitStop Auto Repair in Sarasota FL. It's close enough to where I live in FL so I decided to take my Blazer to him seeing that I'm basically at a wall given my limited experience and time was a big factor given my regular day job.
Ray and the whole team that works there are very good at what they do. I definately recommend his YouTube channel. He didn't do any videos specifically on my Blazer in the 2 weeks he had it, but I never asked and I don't mind if he did or not.

Here's what he found.

Bad spider injector
I had a feeling this was the case, but I wanted to take it to him as is before throwing any more parts cannon at it. I was told that it was fairly clean under the plenum and they suspected multiple injectors not spraying right.

Melted pre-catalyst
I didn't realize the buldge in the exhaust pipe before the main catalyst was also a catalyst. Ray told me that this was a result of the fuel injectors dumping too much fuel into the exhaust. The main catalyst was just fine. He cut off the pre-catalyst, removed the melted substrate, and welded it back on. I'm very happy with the result. I seem to have reclaimed my lost MPGs and it definately has most of its power back.

At this point it was ready to be picked up, but as I started doing some more highway driving at 65 MPH, it began to misfire hard. P0300 with the light flashing. I brought it back to him and he continued to investigate it over the next 2 weeks.
During that time here's what he also found investigating the timing.

Slipped balancer ring
Yep, turns out the outer ring on the harmonic balancer has indeed slipped and it can be turned by hand (I have the old one in my possession). I thought this wasn't the case given how everything seemed to line up when I got the CMP offset as close to 0 as I could. The guys at the shop said I got lucky that it ran afterwards.

Distributor off by 1 tooth
I thought I dropped it back in right by observing the position of the #1 piston at TDC, but I guess not. He lined it up correctly and put a new hold-down clamp replacing the modified one I used to twist the distributor.

Inadequate ignition wires
I think I asked for this problem when I choose the aftermarket DragonFire wires I installed 15k miles ago instead of an OEM design. He said these were measuring a much higher resistance than they should be so he replaced those with a set from ACDelco. I don't know if the gauge of the wire matters, but the DragonFire ones were 8mm and these ACDelco wires are 7mm.

Loose CPK sensor
This is likely my mistake when I installed the replacement. Ray said it wasn't seated all the way, and it had a loose wire that he fixed.

Nondescript intake leak
I was told Ray found an intake leak that was taken care of too. I'm not sure where though. I plan to ask next time I have a chance to speak with him to give an update on how its driving. I so far haven't found anything around the intake manifold where a leak was patched.

After 2 weeks of this, my Blazer was finally ready to be driven home. Low MPG issues seems to have been solved (need to record long term travel data to confirm), poor acceleration/power has been solved (she takes off nice and easy but not too slow now), and the near stalling that occasionally happens when coming to a stop because the RPMs drop too low has finally been solved (been trying to solve that one for almost 2 years now).

The guys at the shop told me that all the misfire problems have been solved except on a cold start. They said for whatever reason on a cold start it has a regular misfire, but after she warms up and starts going the misfires are virtually not there. They said this is likely because of poor fuel quality. I may have picked up some dirty or poorly mixed fuel somwhere. They pulled out a fuel sample from the tank and discovered that it was running on 23% ethanol. Their recommendation was to drive it normally and cycle through the fuel tank, only buy from reputable brands at station that have regular traffic, and run some Techron fuel cleaner through it.

After about 10 days of driving my Blazer normally running errands and joy riding around, I'm now reporting that the misfire still persists. At first it felt pretty solid, no hard rumbles. Now on day 10 I feel it rumbling more than it should when warmed up and idling. It also has this tempement since day 1 where the check engine light will come on at least once for P0300 sometimes flashing sometimes not, but I don't feel it misfiring that hard for it to come on flashing. I shug it off everytime as bad sensor data and just clear the code as I'm driving and it doesn't come again for the rest of the day.

The misfire continues to be a mystery.

What hasn't been done yet is a compression/leakdown test. Ray felt it wasn't necessary, so I took his assessment at face value.
Dash Command tells me that #2, #3, and #4 (mostly #3) still get regular misfire counts.

 

Thanks for the update! Keep us posted! I remain interested in your issues and their solution.

Only comment I will make is that you were definitely not off a tooth on distributor when you had CMP retard = 0. CMP retard is independent of any visual mark on balancer. If CMP retard is correct, distributor is in correct irregardless of anything with the balancer . I think you know this!

 

A new interesting development has occured.

#3 is still misfiring regularly with a rough idle, and I found that bank 1 LTFT is running at 20% on idle and bank 2 is at 12%. So the fuel system is running pretty lean. As soon as any engine load is applied the fuel trims go back to normal.

I was getting ready to head out on a joy ride to collect some more fuel data, but I found that the coolant was running low when I checked all the fluids. It's also pretty dirty. It shouldn't be dirty because I had just overhauled the cooling system when I changed out the heater core for the second time last October.

Lean condition, rough idle, mis on #3, low/ dirty coolant... I'm strongly thinking intake or head gasket leak. What do you guys think? I'm looking into one of those checmical testers for detecting combustion gases.