Those fuel trims are very good for an old truck. You add the STFT and LTFT together for a given bank, mindful of sign. You do go from slightly positive to slightly negative as your rpms go up so it’s possible that there is a small vacuum leak but these numbers are not dramatic.


George

 

I hope to get the truck back this evening and can give you updated fuel trims. Those were before I changed the spider which was leaking. Also that was when I only had 9 of the 10 upper manifold hold downs installed. The previous owner crushed the EVAP soleniod and one of the bolt holes. I have put an undamaged upper manifold on it and torqued it to 88 in/lbs.

Here's my plan:
1. Pull the number 1 spark wire and connect my OTC spark tester.
2. Address and issues from that.
3. If still getting misfire then pull number 1 plug. Check compression against previous recorded value of 162.
4. I am thinking about replacing plug to eliminate it as a source of the misfire.
5. I may go to the pick and pull to pick up a throttle body. It seems the issues started when I cleaned it. Misfire is more pronounced when cold so maybe IAC or TPS? I am guessing here.
6. Because of the misfire we are blocked from doing the case relearn.

The shop I use is swamped and Wednesday night someone broke into a customers work truck and damaged the steering column. The truck is parked in front of the shop door. It's a one man operation so lost yesterday to insurance, police reports and working on the disabled van.

I have less than a week before I head out on my.vacation. Time is the one thing I don't have so decisions maybe made on that basis.

 

Running better when warm can mean a couple of things:

Its literally because the engine is warmer: expansion, electronics, etc.

Its because the system transitions to closed loop and fuel delivery is managed by the O2 sensors and not the other sensors and the table values. Does it run better at the moment of closed loop transition?


George

 

The old adage of what did you break when you fixed something else applies here. I removed the spark plugs and wires for removal and reinstall of the headers. I now believe the spider was an issue at higher rpm and loads i.e. climbing hills.

The spark plug wire for cylinder 1 was loose at the plug. Never made a click but got much tighter after I reinstalled it several times. Finally had to squeeze the ring to get it tight.

The constant miss is now only showing up when I slow and sometimes at idle but the more I drove it the better it was. I put in a used plug and will get a new one and replace the spark plug wire.

I am going to check vacuum, compression and test the new wire with my spark tester before I call the install good. I also will get out the fuel pressure gauge and verify those numbers.

I am thinking it's carbon in the cylinder so will add some fuel system cleaner when I fill it up with pure gas today. This will attack possible old gas and a cylinder that may have issues from having fuel leak into it

 

Reviving my old thread to update the group on what I finally found. I had a very bad assumption...you change the timing set out at TDC on the number cylinder !.

This is not correct the instruction say to pull the timing chain cover and rotate the engine till the marks on the cam and crank gear line.

I can't remember why but the drive gear for the balance shaft come out back August 2020 when this began. I tried to line it back up with the balance shaft using the marks not together but across the drive gear.

I will reassemble but I found my oil leak at the front snout as the seal had cut a groove on the harmonic balancer.

 

Sure, I suppose that could throw things out of balance and potentially cause a P0300. But honestly never heard of it as a problem before. Be interested if this cures your P0300. Please be sure to get back to us on that! Sounds like the P0300 came with the timing chain replacement, but crank sensor was definitely disturbed as well - so ????. Will CASE relearn initiate easily now?

 

I should admit that the photo of the dots aligned was second attempt. But I had verified everything else with most being done twice.

In case this is too long to read I been fighting this since August 16th,2020. The first P0300 code was set driving to the nechanics to get a CASE relearn done.

JB Weld held the insert in place and a 2nd CASE relearn was done. That is until I wanted to check the clearance to see if it was less than 0.030". Then it started spinning again. So I decided to go back to the timing chain install. In addition to the insert not holding I wanted to eliminate a bad chain or bad install.

I didn't report on the MAF changes, thottle body changes and the struggle to get the exhaust leaks eliminated. Always with 900-2700 misfires on my 27 miles to work.

Just to recap:

• 2 distributors OEM and Summit billet
• 2 sets of spark plugs
• 2 sets of wires
• 3 MAF sensors - one I had in my garage and from 1/2 price day at pick n pull
• 2 spiders 2nd for sure AC Delco cured #6 misfires
• exhaustive multiple searches for vacuum leaks even the the vacuum at idle is 18-19 inches or more
• changed the fuel filter due mileage but no change
• Multiple doses of fuel injector no affect on the misfires but the mileage would go up
• Seafoamed the engine twice actually made things worse for several hundred miles
• added Seafoam to crankcase with no change to the oil pressure.
• used 15w-40 diesel oil at an oil change no change in misfires so not likely to be worn bearings
• pulled both valve covers and turn the engine by hand with no issues noted..
• Started the engine and let idle w/o valve covers no issues noted but I relearned the roller lifters don't rotate.
• broke MAP sensor and replace with AC Delco need to learn how to remove for inspection.
• I admit the Pacesetter header have burned several plug wires until I perfected the routing.
• also replaced the headers with a new set and had power coated for thermal barrier. This is decision I would change now..would get OEM exhaust manifolds
• Changed EGR gasket and verified that it work as it should with multimeter
• Replaced squeaking alternator with new to me used on voltage is 13.3-13.5

 

‘67 Camaro, nice!


George

 

Update.....Got really frustrated with the truck and was living with issues. Tried to replace the oil pan gasket with a leak and installed leak on the passenger side CV axle seal.

Drove it sparingly and this Thanksgiving my friend I've known 3rd grade was in town. Dropped the front diff and oil pan.

The weather was lovely. Double checked balance shaft to cam gear alignment and timing gear alignment. All was well and torque wrench clicked at bolt torques for the timing gear. Placed the new timing cover and oil pan on. Found massive leaks so stooped. Life, work and weather delayed me till about Christmas.

Was supposed to work on it during a Christmas break. My son's came back for Christmas...got sidetracked from.a simple oil change to replacing CV axle on my youngest son's Teailblazer. Discovered this on Christmas eve after the parts stores closed.

My oldest son did the brakes on my 5 speed truck...wanted to show me how an apprentice dealership tech did it. I cooked the holiday meal but the day after Christmas the boys went back to their home or college.

The youngest drove the punishment truck back to school. My 97 Suvurban is not a popular choice to drive. Fixed the Tailblazer over the following weekend and met him halfway and swapped trucks. Now I have to go back to work so no progress on the ZR2 but I will start another post for the final solution

 

Update finally solved the misfire:

During replacement of timing cover and oil pan gasket.

1. Confirmed alignment of the cam gear and balance shaft gear.
2. Timing gears alignment confirmed and bolt torque on cam verified.
3. Balancer bolt bolt and pulley bolts torques were set properly...found a way to hold engine from rotating while working solo. Heard clicks on torque wrench..

The weather while I was working on this.

Statrted engine and it idled ok but definitely need the crank cam relearn done.

Tried to drive the truck but it lacked power and took full thottle to climb hills and highway speeds were a no go.

Looked at the air filter, MAF sensor and general issues. Checked fuel pressure and decided to fill truck with fresh gas and change fuel filter...ran better but didn't cure problems.

Weather got cold but IAT looked funky i.e. 80+ degrees on a 16 degree day. Temps are Fahrenheit. Pulled connection and truck run good enough to get it to the mechanic. He did the relearn and the ran better. I swapped the IAT from my 5 spd truck and the truck would run up to highway speeds but still lacked power.

I drove a day or two chasing misfires on cylinder 1, 4 and 6 when the first clue showed up. An EGR code....the memory of loosening the EGR for removal before I got the hoses off the water pump. I had to remove the water pump for timing chain cover change.

Replaced gasket a properly torqued it and suddenly the truck is drivable. Still misfiring more than I like and fuel trims have wild swings. Aso for lack of a better term the fuel trims would freeze when high loads were applied i.e. getting on the highway.

Now I have a intermittent P0101 and P0410 code with more misfires than I but mostly on cylinder 1 and 4. Continue checking out issues swap the MAF between my 2 Blazers without a change in either in how they drove. 5spd truck no issues and no record of misfires will see low single digits in current intermittently but not recorded to history.

I pulled off the air intake system and found what the alternator whine was hiding

The boot at manifold was split.

Better picture of the issue

I thought I was hearing a vacuum leak but with engine running and hood open the whine on the 200+ amp alternator fan I missed this. Replaced with AC Delco part. Drove for a couple of weeks still chasing misfires but much fewer of them. The fuel trims and power were much closer to normal.

Pulled a 3rd MAF sensor from box of things I might need someday...cleaned and installed it without change in the truck performance. When I was pulling my air intake to find out if both of air injection check valves bad I found the final piece to this puzzle.

It is I believe an artifact from the cold intake that was one this truck when I bought it. There was a black flat rubber gasket on the thottle body which lifted the air horn slightly. And it wasnt sitting right i.e. back higher than front. Pulled that and air horn went on easy and sits level. The truck runs better i.e.about 1 mpg more hwy. And misfires are way down with only 23 recorded on cylinder 1 this morning and 4 had 14. Those happened at start up so not worried.

The P0101 is still there intermittently so I am thinking wiring issue but will diagnose properly. Pretty with MAF all running the same not them.

The P0410 is a bastard as I think both check valves are bad and feed air at cylinders 1 and 4. Also the salvage yard air pump is done...only sparks with 12v applied.

But I calling the misfire fixed.

TLDR Found many little issues perhaps loose crank pulley and balancer bolt, vacuum leak on PCV hose that became large enough to notice, Aftermarket IAT sensor was reading high and would stick and an extra gasket on thottle was causing a small leak of pirate air.