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Solved - 4.3 CPI Won't Idle

895 Views 8 Replies 3 Participants Last post by  Alex_McG
Update - truck is back on the road(y) Harmonic balancer had slipped ~90°, replaced it and she’s running better than ever after all the other stuff I cleaned/replaced.

I recently bought a 1994 S10 Blazer 2wd with a 4.3 CPI, and it needed new freeze plugs and a fuel pressure regulator among other things, so I pulled the motor as I detailed in my member projects post. I got everything back together, and the truck won't idle. I know my timing isn't quite correct, but I can’t get it to run long enough to check it.

Anyways, during troubleshooting this weekend I found that the truck has weak spark on all plug wires and coil - it's orange with a bit of blue at the end rather than pure blue. The only ignition component I hadn't changed was the coil, and being only $25-30 I went ahead and put a new one in which improved the spark, but it's still orange. New wires, plugs, coil, and distributor all went in during the refresh, and I cleaned the 2 ground on the back of the block, the one at the front which goes directly to the negative of the battery, and the fuel pump ground and have verified that the block does have a solid ground to the battery. Battery is also brand new, and the alternator puts out ~14.2-14.3v when I can get it to run. Fuel filter was also replaced and pressure hits ~60-63 while running, but after 10 minutes leaks down to ~43 - I know this is out of spec and likely means my fuel pump is leaking, but it shouldn't be bad enough to stop it from running - it drove relatively fine when I bought it and was leaking down to 20psi in ~3 seconds because of the leaky FPR.

Anyone have any ideas for me to check next? The distributor is a WAI global because none of the shops had any AC Delco in stock, but the WAI has good reviews - I haven't checked the wiring to the dizzy yet so that's next. I cleaned the IAC and MAP sensor, EGR valve, all of the electrical connections, and I'm not getting any CEL codes. Weak spark aside, is it possible that despite replacing my FPR and nut kit that the actual injector is malfunctioning and pouring too much fuel? My poppets don't leak but I haven't checked the spray pattern on them, so I may need to take the plenum back apart and watch each of them fire. Any help is greatly appreciated, I've spent hours and hours reading and have tried just about everything.
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Well I drained the oil and it was full of gas - I have been cranking the thing a ton over the past 2 weeks with bad spark and bad timing, so makes sense. Plus, this was the first fill & flush after washing out the coolant from doing my intake gasket, so I’m going to change the oil another time or two.

I believe I found my weak spark - the connections on the new coil fit tightly and weren’t fully seated, and I cleaned a few more connections. Spark is blue now!

Hoping that the combination of fixing the spark and getting the gas out of my oil will be just what she needs, it did seem to be too rich to run as it’d fire up most easily with the pedal to the floor, no one particular cylinder is missing or has a worse looking plug and I’ve replaced the FPR & nut kit in my CPI system. Will update tonight
Here’s a video of a start attempt if that helps.. kinda seems like its hydrolocking from fuel, guess I may have to pull the plenum again

edit: pulled all the plugs and cranked it, and cylinder 4 is wet around the plug hole whereas all others are dry - possible sticking poppet?
I’m starting to worry my timing chain may have jumped a tooth - I recall a somewhat loud pop sound at one point while turning the crank pulley to remove the torque converter. Though because I’ve been able to start it and rev it up a bit and it sounds good/smooth I’m doubtful this is my problem. I’ll try turning the crank a bit back and forth tonight and see if there’s play in the dizzy rotor.

I’m shooting in the dark here, no idea if that’s even a possibility, but because I have good fuel pressure, spark, close enough timing and it ran before I worked on it I’m running out of ideas.
Well when I turn the crank back and forth, there’s 5-8° of slop before the distributor rotor starts turning… crank turns real easy, then I feel/hear a catch and it stiffens up a bit when the rotor starts turning. Am I taking it back apart? Time for more reading… honestly I don’t mind doing it if it’s the definitive answer to my problem. It doesn’t rattle though, may just be slop in the dizzy gear?

Also, my spark is no longer blue, must’ve been a fluke lol. Back to hunting that down..
I FOUND IT! What a relief. My harmonic balancer has shifted around 90° clockwise from where it should be. Been chasing this for weeks now.

When failing to be able to see/feel the #1 piston to check TDC, I remembered I held onto a cheap ebay inspection camera my grandmother got me for Christmas 6+ years ago.. opened it for the first time and clear as day TDC was 90° off. Going to bite the bullet and replace it despite being temped to just mark the new TDC and send it.

Based on the shiny metal exposed, I suspect it slipped while I was working on it. It’s currently at TDC, so you can see how far off it was.
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Glad you figured it out! Slipped balancers can make you chase your tail.
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4.3 balancers have 2 marks about 90 degrees apart. In an S-series you use the second one to 'go by'. (When correctly set, the first mark is at about 5:00. The first mark is for use in an Astro Van, to by viewed from below the van.)

I don't think your balancer "slipped" at all. You were using the wrong mark.
4.3 balancers have 2 marks about 90 degrees apart. In an S-series you use the second one to 'go by'. (When correctly set, the first mark is at about 5:00. The first mark is for use in an Astro Van, to by viewed from below the van.)

I don't think your balancer "slipped" at all. You were using the wrong mark.
I put a camera in cylinder 1 and checked TDC - I had marked the 2nd (correct) mark with silver sharpie which is what you see in the pic, and you can barely see the edge of the 1st mark on the far right side. Put on a new balancer, timed it and she fired right up and runs like a dream.
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