90 blazer TBI timing issue

[THopper]

I have a 90 k5 tbi 350. It has been running good. I re timed it and made sure everything was good. I advanced it 2*. It had a hiccup off the line but ran strong and smooth through the rest of the power band.

I live at the top of a hill. Coming home Saturday night, I turned up my street and the motor sort of backfired/ hickup'd and then started running like ****. I feathered the throttle to get it up the hill and as soon as I let off at the top it died. I coasted up to the curb next to my house and just left it be and went inside. I came out the next day and started it up. drove it into the driveway but it was running and idling rough.

I unplugged the timing wire and checked the timing. it wasn't even close. Off like 40*+. I checked TDC and made sure the distributer was still stabbed correctly. I can time in with the timing wire disconnected and runs good. Turn the motor off and plug the timing wire it and it runs like **** again timing jumps all over and just wont smooth out. vacuum lines are all connected and cant find any vacuum leaks.

Any ideas are appreciated and I've searched but I can't find anything similar but there's lots of other info out there. Thanks in advance.

 

[dyeager535]

What's the fuel spray look like out of the injectors?

Timing jumping all over the place makes me think misfire, which will result in the knock sensor retarding timing a ton. However 40* is way excessive at idle, nothing should be causing it to go that high, timing is ECM controlled, it MIGHT hit 40* under moderate throttle and no load such as cruising or in park with the engine revved up. No idea what max timing is in the ECM.

 

[THopper]

The more I search and read, the more I'm think my distributor has gone bad. Anyone have delt with distributors going bad on them before? It looks like napa trying to get $100+ for their's but I can order one from jegs for 65ish. The problem is I'm trying to go to the beach Friday night for the weekend. Does anyone think it worth the 100 bucks?

 

[readymix]

Mine failed when I live in Illinois around 2003 or 2004. It's usually that the permanent magnet that runs the reluctor wheel loses is magnetism, or the bushings go bad.

 

[dyeager535]

It's not like you can't test the distributor, google GM HEI distributor testing and you'll probably find the procedures.

Any failures I can think of relating to distributor have always been a stalling situation, as in it wouldn't run. Bad pickup, bad reluctor, bad module, etc.

If you have a distributor issue at this point, definitely smarter IMO to just replace the whole thing, but I'd not be convinced that IS your problem until I tested it. There is no physical advance in the distributor, the only way it can be bouncing around is if something is loose, or the ECM is doing something in response to another problem.

 

[4X4HIGH]

Sounds to me like you have a spark module giving you issues, this is the black square box mounted on a bracket to the right (passenger side) of the engine next to the TBI unit. This usually will give a code 42. Try removing the connector and cleaning the terminals and then reconnecting.

 

[THopper]

Just to update everyone, if you guys even care!?! I successfully made my beach trip in the blazer. I got the K5 running Thursday night and was able to hit the road Friday after work. I ended up replacing the distributor with a local junk yard one. It looked a little dirty but I cleaned it up, put my electronics on it and went from there. I had a few issues with timing it because I drop my timing light and it decided to no longer time things correctly. I didn't know this at first but had a hunch because it wasn't timing right off the light. The timing mark wasn't even near the timing marks. I barrowed one from a friend down the road and boom! She liked me again. The last issue I now have to deal with is there is a substantial stutter/ power drop on take off. When hitting the throttle on acceleration, it pops/stutters and then comes on strong and smooth through the rest of the rpm's. It has an old tbi spacer and I'm going to start by removing that and see what happens. Any advice?

 

[41565chevelle]

Thanks for the update. You help the whole bunch of us when these things pop up. We all learn from each other.

 

[cuervo]

Just to update everyone, if you guys even care!?! I successfully made my beach trip in the blazer. I got the K5 running Thursday night and was able to hit the road Friday after work. I ended up replacing the distributor with a local junk yard one. It looked a little dirty but I cleaned it up, put my electronics on it and went from there. I had a few issues with timing it because I drop my timing light and it decided to no longer time things correctly. I didn't know this at first but had a hunch because it wasn't timing right off the light. The timing mark wasn't even near the timing marks. I barrowed one from a friend down the road and boom! She liked me again. The last issue I now have to deal with is there is a substantial stutter/ power drop on take off. When hitting the throttle on acceleration, it pops/stutters and then comes on strong and smooth through the rest of the rpm's. It has an old tbi spacer and I'm going to start by removing that and see what happens. Any advice?

Vacuum leak?

 

[THopper]

So, here's my update, sold the K5. checked for vacuum leaks, couldn't find any. Just for fun, replaced cap, rotor, wires and plugs because one got burnt a little. After timing it, I left the #1 wires hang out to much and it was resting on the exhaust manifold.

Stopped off a Pick n Pull and grabbed some stock length bolts for the throttle body. Got home. Received a phone call and guy and came and bought it. gave him the new to me bolts and off he went.

Now my 4L80 is rebuilt and sitting at the shop ready to pick up. My suburban will be mobile again. Sucks to dell one rig to fund another but that's life.