[420blazer03]

Every time i think i fixed it, it comes back. Here’s a list (from memory) of all the parts Ive replaced in the 20k miles that Ive owned this 2003 blazer.
-spark plugs, wires, distributor assembly
-coil pack, ignition control module
(Essentially replaced the entire ignition system)
-crank position sensor
-maf sensor
-spider injectors
-intake manifold gaskets
-rear main seal
-radiator
And more Im sure. The engine light comes and goes. It makes a rattling noise under acceleration only in the 1200-2500 rpm range. bit of rough idle. Slight hesitation. Im tired of throwing parts at it.

i was wondering if an exhaust leak at the y-pipe after the manifolds can cause a misfire? I had to remove the exhaust when I pulled the transmission and one of the studs on each side got stripped so two nuts, one on each flange, are not seated. Could this cause an exhaust leak significant enough to throw of o2 sensor readings and mess up the A/F ratio?

Im beginning to think it may be a mechanical issue, either timing chain or valves. Ive done a compression test but the engine was cold and it got up to about 150 psi but quickly leaked down. Is that normal?

sorry for the disorganized flurry of information, just getting fed up with this machine. Any help is appreciated. Maybe its time to let the pros fix it.

 

[Rhotpursuit]

Did you do a relearn?

 

[420blazer03]

Did you do a relearn?

No, how do i do that? And what exactly does that mean?

 

[Rhotpursuit]

@oldeerslayer @Harley you guys can explain it better than I can…a little help please.

 

[oldeerslayer]

When you replace the Crank Position sensor you need to do a relearn. Problem is unless you have access to a high end bi-directional scanner you'll need to pay someone to do it. Each individual sensor takes a certain amount of time in micro seconds to get the signal to the PCM. When you replace one the PCM can measure that time when doing a relearn and adjust for it.
Yes, if 2 out of 3 exhaust studs aren't tight you could have enough of a leak to throw off that O2 sensor. Emphasis on could.
I didn't see any mention of doing a fuel pressure test or any numbers from one. If your fuel pressure is low it can cause a P0300. Usually under light acceleration. Since you also have a rattle under those conditions I'd throw a knock sensor at it also. The PCM should be retarding the timing as the load increases. Based on input from the knock sensor.

 

[Life is a Enigma]

Also check the crank sensor and make sure the crankshaft is not tapping on the head of it. If it is you may need to use the shims that came with the new crank sensor. And take it out one night get it nice and warm then find a nice dark spot pop the hood and see if you see any arcing from around the spark plug boots.

 

[420blazer03]

When you replace the Crank Position sensor you need to do a relearn. Problem is unless you have access to a high end bi-directional scanner you'll need to pay someone to do it. Each individual sensor takes a certain amount of time in micro seconds to get the signal to the PCM. When you replace one the PCM can measure that time when doing a relearn and adjust for it.
Yes, if 2 out of 3 exhaust studs aren't tight you could have enough of a leak to throw off that O2 sensor. Emphasis on could.
I didn't see any mention of doing a fuel pressure test or any numbers from one. If your fuel pressure is low it can cause a P0300. Usually under light acceleration. Since you also have a rattle under those conditions I'd throw a knock sensor at it also. The PCM should be retarding the timing as the load increases. Based on input from the knock sensor.

I see, would it be too late to do a relearn if I replaced the cps about 10k miles ago? Would I need a new one or can I still have someone relearn it? Also who has the proper scanner to do it?

 

[420blazer03]

Also check the crank sensor and make sure the crankshaft is not tapping on the head of it. If it is you may need to use the shims that came with the new crank sensor. And take it out one night get it nice and warm then find a nice dark spot pop the hood and see if you see any arcing from around the spark plug boots.

Ill check that, i also checked for arcing and haven’t seen anything, i tried moving around some spark plug cables too. At first it was p0301 misfire on cyl 1, then it changed to p0300. I was having a p0101 and p0113 code after doing the injectors but then i sprayed the maf and air temp sensor with maf cleaner and retightened the snorkel fittings and those codes went away, now its just p0300.

 

[Life is a Enigma]

Ill check that, i also checked for arcing and haven’t seen anything, i tried moving around some spark plug cables too. At first it was p0301 misfire on cyl 1, then it changed to p0300. I was having a p0101 and p0113 code after doing the injectors but then i sprayed the maf and air temp sensor with maf cleaner and retightened the snorkel fittings and those codes went away, now its just p0300.

When you put the new spider injectors in sure you didn't mix two injectors up? I did that once I mixed 3 & 5 injectors up and it did run fine but I kept getting a constant misfire p300 when I pulled intake back apart that's when I realized I mix those two up.

 

[420blazer03]

When you put the new spider injectors in sure you didn't mix two injectors up? I did that once I mixed 3 & 5 injectors up and it did run fine but I kept getting a constant misfire p300 when I pulled intake back apart that's when I realized I mix those two up.

I dont think so, I made sure to check everything before closing it up but it’s possible. Ive had this code long before replacing the injectors anyway and seemed to run great after replacing them then started acting up again. I just tested fuel pressure at the test port on the fuel line and it seemed good, held pressure no leakdown problems. The light went away today and seems to be running good but who knows. Tomorrow it might act up again.

 

[420blazer03]

Also another thing worth noting is before I replaced the whole distributor I replaced the gear on my old one since it was quite worn and it seemed to run wonderfully after that, smooth as butter and no strange noises at all. Then it started making that rattling about a week later.

 

[420blazer03]

Finally. After hundreds and hundreds of dollars of parts, all I needed was a distributor rotor from a ‘85 ford to fix the problem. Took the brass contact off the rotor and super glued it on to my rotor. Engine runs smooth as butter. I believe it was a stickied thread about how the stock distributors have bad phasing and the wider tip of the ford rotor fixed the problem. Such a pain in the effin ay that they would design it like that straight out the factory.

 

[944v8indfw]

Have been following the thread. As I recall from reading maybe 10 years ago the fix was the Ford piece or slot the hold down on the distributor for phasing but a scan tool that showed live data was needed for the slot mod. Nice to see a report back for future visitors.

 

[420blazer03]

Have been following the thread. As I recall from reading maybe 10 years ago the fix was the Ford piece or slot the hold down on the distributor for phasing but a scan tool that showed live data was needed for the slot mod. Nice to see a report back for future visitors.

Yeah I would have never in a million years figured that one out on my own. Glad that people smarter than me found that. Its a shame to think how many of these trucks were abandoned for something so stupid yet so simple. This should be among the first things to try when one encounters a p0300 on an s10 or any 4.3 i suppose. Im not sure if the v8s have this issue. Im just glad to finally have my blazer running good. A significant power increase too, I barely have to hold the pedal down to go up a hill. These are fantastic engines with the proper modifications.

 

[Rhotpursuit]

@Crew Cab Sonoma did a lot of cool mods. Seems to me he experimented with rotor mods. It would be worth the time to read thru his threads.

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[420blazer03]

Its back again

 

[944v8indfw]

Might be time to research the hold down clamp slot mod.

 

[oldeerslayer]

You'll need a scanner capable of reading "camshaft retard angle". Don't ask me why they call it that but it's the relation ship between the camshaft position and the spark timing. The scanner is supposed to read it as 0°+ or- 2°.
Some scanners use a slightly different term. "cam retard angle" is GM's language.

 

[420blazer03]

Its just weird how when i do something to it it runs great for a little while then comes back again. The SES light goes on and off. Sometimes itll stay off for a couple days then come back on but I definitely feel it misfiring. Sometimes it’ll “skip” when driving at highway speeds, has a bit of a rough idle and some hesitation. Im starting to suspect fuel pump or lifters. I took it to firestone today, they’re even more clueless than me. They tried to tell me the brake light codes c0xxx were misfires and I had to correct the guy! I might take it to another mechanic to do the crankshaft position relearn, could that be the issue?

 

[420blazer03]

You'll need a scanner capable of reading "camshaft retard angle". Don't ask me why they call it that but it's the relation ship between the camshaft position and the spark timing. The scanner is supposed to read it as 0°+ or- 2°.
Some scanners use a slightly different term. "cam retard angle" is GM's language.

So this would tell me if the distributor is off some teeth?