When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
New lifters, resurfaced heads, put back together over weekend and the car is hesitating and sputtering through the lower RPM range. Acting as if there is a vacuum leak. Sprayed brake cleaner around the intake and vacuum fittings while running and nothing changed.
Data log is attached. The O2 sensor readings are different.
Is it hunting at idle or having trouble when you are driving it? I assume it's having trouble at idle as you never moved the car during the log.
Can you warm it up to normal operating temp, start logging it, let it idle for a few minutes not touching the throttle, then upload it?
The cold start has all the trims locked at 128, O2's were not up to temp, you were playing with the throttle, then when it got close to operating temp for closed loop to start working, you stopped logging it.
I started the car cold and took it out for a drive and ran a new log (attached). Seems to be missing during moderate acceleration. Was not able to go WOT since the roads were wet and car keep breaking loose.
I can see in the log the unstable idle. Comparing it to one of my CC503 logs you can see my idle is much more consistent(flat line). The min/max difference on your idle for the displayed section is 358 while mine is 69.
Your fuel trims look decent. I don't see out of control fueling. ST's are cycling around 128, B1LT showed some elevation around 140, but it's not railed.
My MAP is fairly flat too...compared to your MAP pulsing up and down. My initial question would be.....are you sure you don't have the valves adjusted too tight?
Compression and leakdown testing would be my next suggestions....and maybe double checking the dot to dot between the cam and crank.
As a side note...I envy the scanner update rate on that OBDI PCM. You get way more samples a second than I do on OBDII.
I am not 100% sure on the valves. Retracing what I did, I may have overtightend one valve. I was using the spin method for zero lash and may have been too aggressive on one of them. I will check on Saturday
Thank you
I am not 100% sure on the valves. Retracing what I did, I may have overtightend one valve. I was using the spin method for zero lash and may have been too aggressive on one of them. I will check on Saturday
Thank you
I would try a running adjustment with 1/4 turn preload from zero lash and see where that gets you.
What was the reason for resurfacing the heads? Was it running rough or having issues before the teardown?
If mine was misfiring at idle, I'd look at the primary ignition current with a scope along with the secondary from cylinder one(as a sync pulse) to try and see if all the cylinders are having issues or just specific ones. That gets into having a scope, current clamp, and a couple of other tools to see the waveforms.
Have you scanned the PCM for codes? Some codes don't set the SES light.
Another thing to do would be to create a thread and post the scan log on Camaroz28.com in the LT1 section. Injuneer is pretty good with scan logs and may see something that I'm totally missing.
I use the free 94/95 LT1 Scanning Software - PCM/ABS/SRS available on Camaroz28 forum. I replaced spark plugs last night and car runs 90% better. I was cheap when I put the top end back together and reused the set that only had 1000 miles on them. Don't know if it was the plugs or if I had a loose spark plug wire but now she runs strong. Will rerun a scan in the next couple of days. Injuneer compared a log from 2014 to my last one and his comments are below (2109 comments in bold):
The following data looks OK:
-idle is stable at programmed RPM (800) - still OK
-IAC is in acceptable range at idle (38), and opens up with RPM as it should - still OK, counts down to 29, but no problem
-Coolant temp appears normal (194) - still OK, at 190-deg due to cooler weather
-Intake air temp appears normal (85 while driving, 94 at idle) - still OK, down to 75-deg due to cooler weather
-System voltage is good, always above 13V - still OK
-Closed throttle TPS is in the acceptable rang (0.75V) and WOT as well (4.53V) - still OK, except you never went over 90% throttle, probably due to traction issues
-MAF readings at idle are a little high... might be due to the tune/cam. Used to looking at 6 grams/sec, and you are running 10+ G/Sec. Could also be the result of mods to the MAF calibration table, or a problem with the MAF. The excess air flow at idle corresponds roughly with the PCM's efforts to reduce fuel. - better. MAF at idle is down to ~8.0 grams/second. That reduces the fuel supplied, and may have contributed to a reduction of the excess fuel at low loads. 8 gps is not out of line for the cam
-MAP slightly high at 46kPa, but not out of line with the cam specs. - still OK
-Spark advance at idle, and even under load looks to be on the high side. The increased advance at idle may be the tuner's method of compensating for the cam. - still looks high to me, at 29-deg at idle. Did you ask the tuner about this?
-As noted, you have a lot of knock retard, but the worst incidents (6/7*) are experienced on lifting throttle. Any chance something is banging on the chassis when you let off the throttle? - much worse. Any throttle application, even gentle, produces up to 12-deg of knock retard. Appears the tuner may have reduced the max allowable retard from stock 15-deg to 12-deg. I suspect this is the cause of what you sense as "hesitation" Wouldn't cause "sputtering", but you may be getting additional knock after the system maxes out at 12-deg.
-At idle, the PCM is pulling out 15% fuel on both sides, and another 15% using the short term fuel corrections on the left bank, for a total fuel reduction of 30%. The right side isn't quite as bad, but the long term corrections are bottomed out on both sides. - better. At low loads the PCM is pulling out about 10% fuel using the LTFT's, but no additional with the STFT's. Did you discuss with tuner?
As noted above, the big problem is the high excess fuel at idle, and continuing on into the low load cells. By the time you get to the high load/high RPM cells, the problem has virtually disappeared. In PE mode, defaulting to Cell 15 and LTFT's of 128, your O2 readings are not unreasonably high. Right side is generally just under 900mV, and the left side is generally just above 900mV, although it does reach 945mV on a couple of the WOT pulls. Read cautions above on the accuracy of narrow-band O2 sensors in PE mode. - in high load cells, its adding a small amount of fuel to the left side only, but within normal tolerances. In PE mode, the average O2 readings have dropped a bit below 900 mV, still not lean enough to cause all that knock retard. But - the same old caution, the narrow-band O2 sensors are not accurate at WOT . Could possibly be a bit lean and promoting knock, although a lot of your accel was so gentle it didn't get into PE mode very often (which is even worse, because the PCM is not shifting fro the stoichiometric 14.7:1 to the richer target A/F ratios used in PR mode
I'd provide these comments to your tuner and see if he can think of reasons it would be running extremely rich at idle and in low load cells. - the big question.... 5 years ago, did you provide this analysis to the tuner, to ask for advice?
I am going to review the items noted above with my tuner.
Resurfaced the heads due to a coolant leak in cylinder #1. Small divot in head allowed leak. Replaced all the Ls1 lifters I put in 4 years ago - 1 broke and others were noisy. Replaced with Lt1 lifters. Was running smooth and strong before the leak and the broken lifter.
Thinking of replacing my knock sensor. Original with 158K miles.
02-04-2019, 04:28 PM
Hesitating and sputtering lower RPM (datalog) 
