93 this 350 running very rich

[jshfchtr]

Hey guys, I’ve got a real head scratcher of an issue with my 93 c1500 5.7 truck. Little background on the truck, I picked it up cheap from a former coworker, found the motor low on compression so yanked it out and fully rebuilt it. Fired it up, broke in the new camshaft and drove it around the block a few times (not registered or street ready at the time). It ran flawlessly, parked it for a few weeks and ive been slowly fixing other issues such as brakes, cooling and front end work. I cannot remember when but one of the times I pulled it into my shop I noticed it running extremely rich, rich enough you can’t run it more than a few minutes inside the shop without your eyes watering, black smoke just dumping out the exhaust.

Running extremely rich is the problem I’m trying to solve, so far I’ve replaced coolant sensor, heated oxygen sensor, 3 different map sensors, fuel pressure regulator and rebuilt the throttle body. Still runs pig rich. Im lucky enough to have a friend with a perfectly running 91 tbi 350 truck he doesn’t use much that he loaned me and I spent the day swapping each and every part related to fueling from his truck to mine and still never got it to idle cleanly. I swapped coolant sensors, map sensor, entire throttle body, and ECM from his truck to mine. I also verified ignition timing at 0 degrees with spout wire disconnected, ground wires have been cleaned with new terminals and added an extra block to frame ground. I’m sure I’m forgetting other things I’ve tried, ive been chasing this problem for months.

I do have an OBD1 data logging scan tool and every sensor seems to read correctly, fuel pressure is a steady 12 psi. I am getting code 43, i did replace the knock sensor to try and fix that but still get the code immediately with both ECM’s I’ve tried so that seems to be a wire or connector problem. The previous owner also swapped the 4l60 trans for a 700r4 at one point so I have a perpetual CEL light on. He drove the truck 30,000 miles with this trans without issue so I doubt thats my issue but putting the right tranny in it is on the fix list after the motor issue is figured out.

Im at wits end with this truck and too financially invested to give up on it. If there is any advice or suggestions or something I’m overlooking please let me know

 

[95 Tahoe]

Check the spray patterns on the injectors. I had an engine go from running good to not. A plug wire fell off.

 

[PWC Repair]

Sometimes an ignition issue can have you chasing a non-existent fuel issue. Start it up and point an infra red temp gun at every exhaust port. Keep going around as it warms up watching for one or more that might be staying cool. If you find any like that, check those spark plugs. Maybe fueling is actually OK but your just not igniting all the fuel properly.....

 

[Schurkey]

1. Really good chance you've poisoned the catalyst. MAYBE it will come back to life once you get the engine running properly.

2. EGR works properly?

3. Electronic spark advance works properly?

4. Cylinder balance test. Find out which cylinder(s) are not running properly.

5. You used the correct TBI-specific intake manifold gaskets...right?

I noticed it running extremely rich, rich enough you can’t run it more than a few minutes inside the shop without your eyes watering, black smoke just dumping out the exhaust.

Running extremely rich is the problem I’m trying to solve, so far I’ve replaced coolant sensor, heated oxygen sensor, 3 different map sensors, fuel pressure regulator and rebuilt the throttle body.

6. Did you swap distributors? Have you tested the coil output voltage with a spark-tester calibrated for HEI?

7. You verified the timing mark on the damper aligns with the timing pointer on the timing cover when #1 is at TDC...right? Any chance you used the wrong damper when the engine was assembled?

I am getting code 43, i did replace the knock sensor to try and fix that but still get the code immediately with both ECM’s I’ve tried so that seems to be a wire or connector problem.

Download the service manual set from the links on this site. Follow the official diagnostic procedure for Code 43.

 

[jshfchtr]

Thanks for the suggestions, i did use a whole throttle body with the injectors from the good running truck so I believe I can rule out injectors. I haven’t looked into ignition system yet, I will test how far the spark jumps this afternoon, maybe even swap the distributor with a known good one. Spark advance seems to be working, I set the advance at 0 with the spout wire disconnected and with the spout wire connected the advance moved up a good amount but I didn’t note the exact reading. EGR valve holds vacuum and I cut a beer can block off plate for it to test that as well, no dice there. I couldn’t tell you for sure on the manifold gaskets, they came in the gasket kit I ordered when I built the motor but I did sprayed brake clean around hunting for a vacuum leak and never found one. Engine vacuum reads 18-19 inches at idle and is very steady. The damper is the original one, I’ll check that to see if it has slipped this afternoon as well.

 

[Schurkey]

DO NOT use brake cleaner to check for vacuum leaks. Some brake cleaners produce poisonous gas that can injure or kill you. Other brake cleaners don't burn, therefore don't enrich the mixture, therefore don't give much if any indication of a leak.

I use aerosol carb cleaner. Others use an unlit propane torch.

 

[jshfchtr]

Sorry for a late response, this Midwest heat makes it miserable for after work wrenching. I have the truck in the shop now, so far I have verified TDC on number 1, the balancer is perfectly lines up with #1 piston at TDC. I also checked spark, I don't have a spark gap tool, I will buy one if it is necessary but I did remove all the plugs and watched the spark by holding the plug to the valve cover. Each cylinder had an orange spark with an audible snap. I also compression tested each cylinder while the plugs were out and each cylinder was in the 100-120 range (I doubt the rings are completely seated with extremely little on road driving). I did go over the exhaust manifold with a IR thermometer and each cylinder was within 50ish degrees of each other. I'll attach a picture of the plugs, they are organized in order with my finger pointing at #1. Most the plugs look to be on the rich side but #8 is extremely rich.

I am now wondering if I possibly had a problem, solved it already and was just dealing with fouled plugs. I'm heading to the parts store now to pick up a new set and see what happens. If there's a reasonably priced spark gap tool I'll grab one as well and post with my results.

 

[Schurkey]

I also checked spark, I don't have a spark gap tool, I will buy one if it is necessary

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I also compression tested each cylinder while the plugs were out and each cylinder was in the 100-120 range (I doubt the rings are completely seated with extremely little on road driving).

Seems low, depending on your altitude, your cam choice, and about a dozen other factors. The "old" engine had "low compression", the "new" engine has "low compression"...is your compression gauge accurate?

I'd expect rings to be seated with 10--20 miles of "on road" driving, if you're doing it right.

I did go over the exhaust manifold with a IR thermometer and each cylinder was within 50ish degrees of each other.

That sounds good.

I am now wondering if I possibly had a problem, solved it already and was just dealing with fouled plugs. I'm heading to the parts store now to pick up a new set and see what happens. If there's a reasonably priced spark gap tool I'll grab one as well and post with my results.

Also sounds good, although low-mileage fouled plugs seem suspicious.

I would probably have tried cleaning the "fouled" plugs with a propane torch. Yellow is deposits burning off. Orange is done, or "nearly done".

 

[jshfchtr]

The "old" engine had 3 broken piston rings, Ive known the previous owner for 10 years and he doesn't believe in regular maintenance. He admitted to me in the 30,000 miles he's driven the truck he never once changed the oil just topped it off when low.

I haven't had a chance to really drive the truck yet, besides the original engine trouble the truck also needed a full brake rebuild, front end work and a set of tires before truly being safe on the road. Around the block a dozen or so times and pulling it in and out of the shop is the extent of me driving it. Maybe 10 miles on the new engine and an hour or two of idling/testing. I'm tempted to chance a ticket and just stab it on the highway for some "spirited" driving to really get the engine broke in and see if that helps anything.

New plugs didn't fix a thing, within a few minutes of idling it was puffing smoke out the exhaust pipe. I used a good matco brand compression tester, I do have a cheaper one as well. I ordered that spark gap tester and will have it in a few days, when that shows up I'll check spark and use my other compression tester and post back the results.

 

[jshfchtr]

Ok, I either fixed it or found a major clue in the most unorthodox of manners. In an act of unusual frustration for me, I dropped the transmission into low gear and ripped it wide open around the block and let it return to idle without using the brakes, a method of seating rings a machinist once told me of. After 3 trips around the block in this manner (and accidently tapping the rev limiter twice) I pulled it back in the shop and.... NO MORE SMOKE! Could it have just been a sticky ring that didn't want to seat? Catalytic converter that hasn't reached temp to burn off extra fuel in it?

This could be a fluke as well, I'm going to leave it in the shop and let it completely cool off and try it again in a few hours. Hopefully it idles cleanly and I can finally move on to it's other issues.