Alright guys this has been a head scratcher for me.

picked this blazer up mostly clean but obviously flawed. Sounded great when I bought it for $800 from a mechanic🤣. They said it needed a radiator and that the egr piping supposedly melted and melted the harness on the passenger side now he has it half a$$ back together with crimped ends I know I need a new harness and plans to replace it soon. And he removed any pipes that connected the egr to the exhaust manifolds not properly just cut them and clamped the ends. I’ve seen people talking about blocking them off and not having much issues. Just not sure if it’ll fix my issue or not.

Pretty sure I removed the exhaust wrap from the passenger side where he has it clamped and might have caused it to leak again. That said I can’t find any vacuum leaks or anything.

with the maf unplugged it runs a tad better and the blinking engine light goes away. Cylinder 2 miss and multi cylinder miss doesn’t pop up on the reader. Plug maf in and codes comes back. Maf dosent change fuel trims when plugged in or not. But does show a reading and was swapped for a known good one.

replaced the distributor maybe 2months ago with a completely new unit. Rotor and cap. The old distributor gears were allmost gone. Replaced all but the 2 spark plugs on drivers side. Has About 180k. Struggles to get up a slight incline sometimes when cold and lacks power and wants to fall on its face more when cold coming to stop lights hard to get back going sometimes. Never stalled.

checked the fuel plenum to the best of my ability to see if I could see any leaks on the spider injector only removed throttle body not entire plenum cover plans to do that tommorow and also compression test.

sorry I know that’s a lot just trying to make sure I’m covering everything any help would be appreciated.



Codes thrown with maf plugged in

 

the P0300 and P0302 codes are misfire codes. Run compression check and look at spark plugs (carboned up, not carboned up, etc) before proceeding with anything. Report please. Also be aware that a P0300 or P0302 misfire code present can prevent PCM from getting to a mode where other codes may or may not show up. When diagnosing you ALWAYS start with the lowest numbered code.

Unplugging MAF sensor prevents PCM from operating normally. Doesn't mean that P0300 or P0302 or any other code that goes away when MAF is unplugged is fixed - they are just ignored.

Is firing order correct? Easy to flip two of the wires at the distributor (1 and 3). Go with numbers molded into the cap.

Is distributor back in correctly? Measure cam sensor retard with a capable scanner. Should be zero +/- 2 degrees. Rotor needs to be pointing correctly when the crank sensor tells PCM to send the spark or you can get a misfire.

Any exhaust leaks screw up the O2 sensor readings (and subsequently fuel trims), so if you have any leaks then those readings don't matter. Furthermore, O2 sensor and fuel trim readings are constantly cycling up and down, so a capture of their value at any instant is quite often less than helpful. Get used to plotting O2 sensor and fuel trim readings over time if you want to look at them.

Really don't think the plumbing you mention (especially because you mention the passenger exhaust manifold) has anything to do with the EGR. EGR has one pipe coming from the rear of the driver's exhaust manifold only. However each manifold has a one-way check valve for the A.I.R. system in the front of the exhaust manifolds. These tend to burn out internally and then the hot exhaust cooks the rubber connections and also travels down the pipes to the A.I.R pump/valves and will ruin them also. This happened to me.

Maybe someone broke off the check valves from the short tubing coming from the manifolds and bent them over trying to seal them. They could be plugged off so they don't leak, but it will still eventually set a code P0410 for A.I.R not working (not a code that you showed - this code probably requires no P0300 and takes a while to set). I would recommend replacing the missing parts and fixing exhaust leaks before worrying about fuel trims. If you are lucky enough to still have the check valves attached to the tubes, I can tell you how to get them off for replacement. If not, it's either junkyard or some very expensive new parts.

Know that he AIR system will not affect performance when vehicle fuel injection is in open loop. Does it misfire during the first 30 seconds of operation from a cold start. If it does misfire, then the AIR system is not causing your basic problem.

Let me know if any of this helps

 

Here is why static one-time O2 sensor and fuel trim readings are worthless in my opinion. This is normal operation with fuel mix being controlled at optimum. Cycles back and forth across 0.41V. This also causes fuel trims to cycle. What good is knowing the voltage at one point in time.

 

Drawings showing what has probably been removed from your vehicle (ATTACHED).
1999BlazerAIRPipes.pdf
1999BlazerAIRPipesBank2.pdf

 

The air system does appear to be the lines that are unhooked on the exhaust system. The mechanic or whoever put in weld over it after cutting it off after the check valve.

If I’m understanding correctly you’re saying the way I sent the live data is a hard way to judge. Which is understandable. Sorry I’m still fairly new at understanding the data myself I do have new to provide so we can see the fluctuations if that’s what you mean?

Unfortunately when I replaced the distributor I was unable to set cam retard. My scanner is incapable of doing so I guess. I tried to use my fathers scanner to do it he said that it was out to like 20 I believe but disconnected it and put his scanner away before I could zero it. I know that’s a lot to be off. Maybe Since I just replaced his toilet maybe I can talk him into hooking it back up.
Also putting new distributior in wasn’t all that easy. Was told the balancer might’ve slipped and caused this issue.
Dropped new distributor in with both timing marks lined up Tdc found out it was no longer tdc. Had to shove borescope camera in cylinder 1 and turn engine over till it reached tdc. It was way off the

original timing marks. It fired right up though and have no reason to think it is off time.

did all that to fix distributor off a tooth code think p134
its never came back.



have compression tester getting ready to do all that now and will report back

[img alt="Here’s how the timing marks were when I dropped the new distributor in and fired it up and ran better then the junk distributor. And removed the code red mark is where tdc is now for bottom alignment “finger”
"]https://cimg7.ibsrv.net/gimg/blazerforum.com-vbulletin/920x2000/img_1267_d430f820b6552069b70d65bc448064b55d2513fe. png[/img]
Here’s how the timing marks were when I dropped the new distributor in and fired it up and ran better then the junk distributor. And removed the code red mark is where tdc is now for bottom alignment “finger”

 

Compression test and spark plug inspection is always a good place to start in diagnosing a misfire so please do finish that and report. But with your additional info of cam sensor retard being 20, I'm betting the cam sensor retard being off is the major misfiring issue.

If you had a P1345 (not P134) and it went away after moving the distributor a tooth, then distributor is definitely in correctly. Balancer may not be balanced well, but distributor is in right. So the balancer or distributor being off a tooth is not an issue with the misfire.

Cam sensor retard of 20 degrees is way too much - should be zero. I am 90% sure this is your main misfire problem if it is really 20. The only way for you to correct a new distributor this much (with a stretched out high-mile timing chain) is to replace the distributor hold-down with one for a small block v-8. To secure distributor, you will probably need a longer (metric) hold down bolt and a flat washer. To get the old hold-down off the distributor you will need to remove the distributor from the vehicle. So make sure you can get the distributor back in with the rotor pointing exactly to some mark on the firewall - same as before it is removed. Also index the distributor housing to the rotor so you can get that back correctly as well, but it should be pretty much 3 plug wires evenly out each side when you are done and ready to start it. Counterclockwise on the distributor will advance the cam sensor retard so you might want to nudge it just a slight bit that way before starting.

When checking cam sensor retard, each time you need to raise RPMs above about 2000 and then let idle. Turn distributor until you get to zero and then lock it down. If it now runs good, go out and buy a new cap and rotor as the old one will have electrical tracks in it from the misfiring.

If you already have a bluetooth ODB2 device and Android, then get Car Diagnostic Pro or Torque Pro. Either one is only $10. Car Diagnostic Pro has the Cam Sensor Retard PID built in. Torque Pro - you can add the PID per instructions on this web site (sticky at top of 2nd gen forum). I have both softwares and a few others - all do cam sensor retard. Personally I think Car Diagnostic Pro does the most for money on a 1998-2004 Blazer (GM enhanced PIDS + HVAC, SIR, ABS, etc) but it is not a good one for 1996-1997 Blazers. I see you have a 1999.

Once you have the P0300 and P0302 fixed, you can start dealing with the impending P0410 you will soon be getting. The AIR system injects air into the exhaust to lower emissions at startup. You can either fix the system or ignore the SES light for the impending P0410 - but it will be on. Unfortunately this prevents you from seeing any other problems that might be occurring and turning on the SES light - but they would most likely (no absolutely) still set their code. Your call. Let me know if you want to fix the AIR system.

Only way to get the light off for P0410 without fixing it is to use HP Tuners software to turn off "error reporting" in the PCM for that particular failure. That's a $100 license even if you have the HP Tuners hardware already. I did something similar for the knock sensors on the LS engine in my 2004 Avalanche (never could fix that damn intermittent P0327 so f**k it). Knock sensors still work but just don't turn on the light or set a code when they misbehave.

If you want to subsequently chase fuel trims for any reason, GeorgeLG has it down to a science and I know he really enjoys it (as long as you follow what he says)! I would defer to him if you wish instruction on doing so.

 

i can’t say for sure we revved the engine when I saw the cam sensor retardant at 20 but talked to my dad and will be checking that soon pulled All of the passenger doing drivers shortly can’t expect to remove 3 and or 5 very easily if at all.

Spark plug for cylinder #2 had some signs of firing but probably not recently. It was covered in black I’m honestly not sure if it was carbon. Oil or fuel. Was slightly wet and I tried lighting it and it light after a second or 2 but only for a second. Wiped it off
other plugs looked normal other then some


otherwise it read like shown.

cylinder 2 149
cylinder 4 154
cylinder 6 150

i will note just rembered to mention that the garage put leak stop in the rad not sure if it was for a coolant leak or because the radiator had a minor crack upon my purchase.

i drove my blazer earlier today and just for the heck of it i guess “gave me peice of mind that it wouldn’t start even with fuel relay removed and spark disconnected” but I pressed the shrader valve for fuel and don’t have a drop spray out… when I replaced the distributor I did fuel pressure test and it was within normal and held for the 10 minute span. That was months ago but don’t see how it would be causing it to add so much fuel if the pumps trying to keep up as it is?


the p1345 went away with the install of new distributor never to return. Distributor was installed maybe 3 months ago. Just recently spent $50 for a scanner at Walmart it runs repair soulutions 2 I’m unsure if any other software it works with. I did buy torque pro and haven’t had any luck connecting it to the app I’ll try some more.


would also love to fix everything on this blazer I have a you pull it near me and the skills to tear and redo most of the stuff on here. I’m just 22 years old and still have a lot of learning to do I do have a 99 s10 extreme I body swapped a 03 Sonoma onto the clean frame and now have a carbed 350 small block with turbo 350 trans I’ve put it together completely myself. Unfortunately blazer needed the radiator and it needs some minor things left to do mainly get road legal again.

if I don’t get those readings for the drivers side tonight I will tommorow hate to disturb my older neighbors


also just to confirm loosen my distributor and turning it counter clock wise should drop my 20 down towards 0? I mean doing that worst case is it’ll run a little better I’d imagine.

 

Spark plug 4. Cylinder 6 was just slightly darker then this

Cylinder 2 spark plug

Old distributor that caused the p1345

Gears could almost slice your finger open “old distributor”

 

Yes, if cam sensor retard was negative 20 from stretched timing chain, that should put it closer to zero and it should run better. Problem is that the stock distributor hold down does not allow the distributor to be turned. #4#2 plug looks like oil fouling to me. Put a new one in and it will probably be Ok for some unknown time.

 

Sorry my mistake - oil fouled plug was #2 (not #4). Makes sense with the P0302 misfire.