How do I read a log?
175K miles. Truck sat for ~15 years... Been my project for about a year. I have yet to see it run well for more than 5 mins.
New intake manifold gaskets, Plugs/wires, New injectors, MAP, IAC, rebuilt tranny, spliced wiring harness connectors (injectors, grounds), New dizzy (Delphi?), new ICM (Delphi)
Compression all <10 variance, ~185 psi
Hello 2s9je0af,
If I read the highlighted sentence above and wash it against your new parts list, reading between the lines
I'd guess that the truck runs fine (cold) Open Loop, but starts running poorly once the vintage O2 sensor(s)
warm up & the engine attempts to go into Closed Loop operation?
**
If this is the case, then the specific scenario we are troubleshooting is a good engine that is a victim of a bad
(O2 sensor based) feedback loop. Assuming a stock exhaust with NO leaks, and healthy wiring between
your O2 sensor and your computer, the solution may be as simple as renewing your O2 sensor(s).
Given that it's been 30 years since your truck rolled off the assembly line, it's possible that a long-ago
PO or mechanic accidentally poisoned the O2 sensor by using the wrong silicone sealer. Or back when
the truck was ~15 years old it blew a head gasket, sending coolant down the exhaust, and this poisoned
the sensor. Heads were replaced, but truck never ran quite right afterwards, and this is why it was
parked all those years before you adopted it. Here's a clear, concise article on O2 sensor failures:
(
Walker O2 troubleshooting article)
In this forum the ideal repair is where we analyze the data, follow it wherever it takes us, and replace the
failed component based upon the evidence. But when it comes to consumables that work in extreme
environments (like spark plugs and oxygen sensors) it's perfectly alright to replace the old parts and
then start formal data collection/troubleshooting. Especially given how affordable a decent single-wire
O2 sensor is these days:
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NOTE 1: For your '94 5.7 there are plenty of O2 sensors to choose from. But given the amount of counterfeit parts being seen
in the wild, you should buy them at a brick-&-mortar store, or from a auto parts website like Rock Auto. FWIW, here's where I
was poking around after reading your post:
(
Rock Auto O2 sensor selection for a '94 5.7 C1500)
NOTE 2: If you have already replaced the O2 sensors (but they didn't make it onto your parts list) and
the problem persists, then by all means we need to study the data you have.
I assumed the new intake manifold would make it run amazing. Runs much better when cold, stalls and backfires in closed loop at stop signs. Feels rich/retarded overall to me.
Timing light is 50 years old... but it seems like I had intermittent spark on #1 so I changed the plug wires (admittedly most wires have just been resting on the headers)
*This truck was such a head case IDK how to use tunerpro. I usually change things on my 82 corssfire corvette 1 at a time then look to see if the BLMs stay 115-143 and call it perfect... This truck literally could be haunted.
So far so good. Think of the fresh intake manifold gaskets & fresh wires as laying a good troubleshooting
foundation. I also like the fact that you have already performed a successful compression test.
Let us know what's currently in place for your O2 sensor. (Old, new, single wire, 3 wire, total number of O2
sensors factory installed, etc. Running changes were being made back then, so it's hard to predict from
here exactly what your truck came with.
Best of luck. I'll bet that the talent in here will figure out what's ailing your machine, no matter where the
problem lies.
****
** Open Loop / Closed Loop failure scenarios, from easiest to hardest:
1) Healthy engine, runs good off of computer tables cold, (Open Loop) but runs poorly warmed up. (Good engine is victim of bad feedback loop.)
2) Engine needs maintenance, running with worn parts that have drifted from calibration. Runs bad cold, but runs OK warmed up. (Closed Loop compensation is successful.)
3) Sick engine, runs poorly Cold or Hot. Fix engine first, followed by fixing feedback loop too if there's collateral damage. Could take a couple of passes to sort it out.
