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4.3 running rich, no codes:

Ping Doc, et al:

got an 89 S10 Blazer, Vin Z, TBI, 4.3, 700R4:

new TPS, IAC, cleaned and rebuilt TBI, new FPR , CTS, MAF sensor, O2 sensor. Basically everything but the knock sensor.

I'm running rich as evidenced by the soot-coated exhaust pipe and the smell of gas at the pipe.

Computer throws no codes, I have logged data from WinALDL but am not sure how to interpret it.

Am installing an Air/fuel gauge, but haven't had time to do more than physically mount it due to the weather and having my garage full of crap .

No info on fuel pressure. I would assume a dying fuel pump would put out less fuel and therefore make the engine run lean.

Air filter is a K&N, and is cleaned regularly.

Checked base spark timing as per the manual- disconnect the ESC wire, set timing to 4deg BTDC, reconnect. When I check the timing during operation, it retards to abotu 10deg BTDC. So apparently there is something being told to the ECU to make it retard. I can hear no spark knock or other mechanical noises other than a tapping exhaust pipe or something of the sort at idle, which goes away with application of throttle. Again, haven't had time to investigate.

I'm getting 14MPG, and I bet if I track this down I can get 3 more. She's running REALLY retarded and really rich...

ideas?

Doc- you said something about the HB being off a tad- how would one check for that? I know normally you can pull a plug, put a dowel in the motor, and turn it over by hand till you're at TDC and compare the HB's position re: the timing marks. However, this basically being a smallblock- the spark plugs enter the head at an angle, so that would be a ballpark operation at best.

Reply to
burntkat
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Kat,

Your spark retard is what's causing it to run rich. When you plug in the EST it should ADVANCE from base timing, not retard. Generally speaking, if base is set at 4*BTDC, you should be seeing 12-16* BTDC with EST plugged in.

Pull the KS and have it tested at AZ. If the ESC module isn't getting s signal from the KS, it defaults to max spark retard and could be causing your problems. Wire could also be melted to the exhaust manifold which is common.

Doc

Reply to
"Doc"

I forgot, to check the HB, pull a plug, stick a finger in the plug hole and have someone hand turn the engine till you get pressure. This should get you close enough to know if the HB is off or not.

Doc

Reply to
"Doc"

inline...

I may be off. I know I set it at 4deg BTDC, and after plugging the ESC back together I note approximately 10deg BTDC. We seem to be saying the same thing?!?

Hadn't thought of these. Will check tomorrow, assuming it doesn't rain or I manage to get the crap in the garage cleared out.

Just toko the truck on a quick beer run, and I believe the rattling is throughout the powerband not just at idle. Perhaps this is being registered by the knock sensor as knock?

Thanks for getting back to me on this.

Reply to
burntkat

MAP, GM trucks didn't use a MAF sensor until later years.

Tailpipe color is very misleading, pull a few sparkplugs and check them for color.

Maybe post the most important ones like the readings from the CTS, O2, MAP, TPS and RPM.

And a pinched/restricted fuel return line will put in more. You can't skip parts of the diagnosis and/or assume.

You should be disconnecting the -EST- wire not the ESC wire, they are two entirely different things and serve different functions WRT ignition timing.

The timing moving from 4º BTDC to 10º BTDC is -ADVANCING- not retarding.

Investigate, the knock sensor may be hearing whatever it is that's banging/rattling and retard the timing while you're driving killing your fuel economy.

Actually, you haven't really posted any evidence of either yet.

Make a positive piston stop by gutting out an old sparkplug, tapping the inside bore and threading in a long enough bolt or stud, install the piston stop in #1 sparkplug hole, hand turn the engine one direction until the piston stops against the piston stop, mark the harmonic balancer, hand turn the engine the opposite direction until the piston stops against the piston stop, mark the harmonic balancer, your factory timing mark

-should- lie exactly in between the two marks you made, if not, the balancer has slipped.

One other thing to check is the pole piece inside the distributor, you're looking for cracks in the magnet radiating away from the rivets that hold the laminations of the pole piece together. if you see any cracks, procure a suitable replacement, if that replacement is a remanufactured distributor, examine -it- closely to make certain you're not getting one that also has a cracked pole piece.

Reply to
Neil Nelson

You said it was RETARDING to 10* BTDC; I assumed you made a typo and meant retarding to 10* ATDC. It is in fact ADVANCING to 10* BTDC then?

Doc

a exhaust pipe rattling against a crossmember> is throughout the powerband

Reply to
"Doc"

Near as I can tell.

Hmm-- now I'm wondering if mabe I didn't pull a dumbass and time it to the wrong side.... .. though I would think it would have no power. Engine pulls strong.

Reply to
burntkat

Doc wrote "Pull the KS and have it tested at AZ."

--------------------------------------------------------------- I heard(but have not yet tried) that you can test a knock sensor by rapping the area near the sensor with a wrench and watching the RPMs drop (or not).Anybody familiar with this ? Or you could watch the timing marks while rapping the case I suppose.

Reply to
Brian Orion

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