I recently swapped out my 305TPI (manual) with a 350 (L05, the block used in caprices, older Impalas, etc). The engine has been running fine for the last 2000 or so miles.

Within the last couple weeks, I've noticed it has started to ping within certain throttle ranges (loading the engine). It doesn't ping when maintaining speed, nor does it when it is really romped on.

I checked the timing and its fine (yes, I unplugged the bypass).

The idle: at the same time the pinging started, I noticed that the idle began getting rough (like, dead or weak cylinder rough). However, the power still seems to be there. As well, unplugging the injectors one-by-one reveals sag with every cylinder, leading me to believe that they're all running (a quick test).

I'm also getting codes 36 and 42, leading me to believe that its an ignition problem. Questions: could I be getting either of these codes from running the engine with the bypass unplugged to check the timing? Also, what can I look at or replace given these codes? (You can check the code meanings elsewhere in this site).

Finally, I realize that this could be evidence of a vacuum leak, and I haven't *fully* investigated this yet. I can imagine in order for it to ping like it is, and have the loping idle like it does, it'd have to be a pretty severe leak. Also, I have the 305's original 19# injectors which *could* be causing a lean condition. BUT, the engine has been running fine until recently (and I also truly believe that the engine should run FINE on 19# injectors).

Any suggestions, gurus? Thanks, guys, for your time!

Mangus

 

No one?

 

Bad plug wire?

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

Hi Mangus,
I have gotten those two codes together a few times.Try replacing the MAF burnoff relay it is not very exspensive.I did that and both codes went away. As for the pinging where is your timing set at? Is your knock sensor working? My car also has somewhat of a rough idle but it could be a lot of things I am having some EGR valve problems.

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SLP 1 5/8 Headers,Dual Catco cats,ATR catback exhaust,SLP cold air box,Crane 1:6 roller rockers,Bosch plugs and MSD wires,MSD Coil,Fastchip,Underdrive pulleys,Borg Warner 9 bolt 3:27,Corvette Servo,ROH ZS 17X9.5 Goodyear GSC,s 275/40/17

 

I just read that a knock sensor for the 350 is different than for the 305!

Is this true? (if so, sh*t! how did I miss that?! =)

That could be an issue.