92 Firebird, 305 E, TBI. Complete rebuild with mild comp cam (XR258H). Stock heads, stock TBI, no air pump, gutted converter. Has the stumble on idle as in other threads, but only when warm. No engine codes with the stumble, but getting worse and sometimes dies in gear.

Pulling 17 in Hg from front of TBI at base. Have had trouble with the timing due to idling problems. Vacuum goes down 2 in Hg when the stumble happens (15 in Hg). Car starts easily hot and cold. High RPM performance not there. Put new fuel pump in tank (Airtek) and it is putting out 13 psi just past the fuel filter.

Eventually threw codes 15, 32, and 34. Since the rebuild (about 600 miles), I have replaced the coolant sensor, EGR valve, MAP sensor, new distributor, new MSD wires, new MSD coil, new distributor cap, new IAC, new non-adjustable TPS, new TBI gaskets, fuel pressure regulator, O2 sensor (fuel inj are several years old) in addition to all the new internal parts (even down to new camshaft bearings). The only thing not replaced under the hood has been some of the wierd crap attached to the firewall.

I am running Comp Cams roller rockers, new pushrods, new lifters, new springs, new retainers all from Comp Cams as well. I set the valve lash with the twirl a pushrod method. My Dad (formerly ASE certified but now "out of the game") keeps pushing me to run the valves with the engine running. He talked about using feeler gauges under the rocker arm and listening for the engine load to change.

What size feeler gauges? Has anyone set the lash with this method? I am pulling out what little hair I have left.

 

You really dont need to adjust them while running with hydraulic lifters.
One thing that comes to mind here is the tune. The factory ecm is not too friendly to cam changes. I would seek out a shop that tunes tbi.

 

Solomon at LT1pcmtuning can help you

 

I am taking your advice seriously. In fact, given all of the changes, a tune probably needs to be done anyway. Here is the frustrating part - when I was designing the engine, originally I was going with a different camshaft. The tech from Comp Cams said that the 08-500-8 part number wouldn't need a tune, reviewed my parts list and said everything would work nicely. That is the reason I have been struggling so much with tracing this down. If the tune ends up being the solution, I might just loose my mind! BTW - LT1pcmtuning looks pretty good. Thanks for the tip.

 

there are several ways to adjust valves . i assume you still have hyd. roller lifters . the following has always worked for me . run engine to operating temp. . remove valve covers , install anti-squirt clips on all rocker arms . ( they are cheap , can get at any parts store ) start engine , one at a time adjust all valves untill they stop clattering . you may have to back some up , do not over adjust , engine will quit . after all clatter is gone one by one back off each valve till you hear a ticking from that valve . then slowly tighten each valve slowly ( do not let socket & rachet rest on rocker arm ) tighten untill they are quiet ( did i say slow on the tightening ? ) then tighten 1/2 to 3/4 of a turn more . go back and repeat untill you are happy . i hope you have new nuts that you used . other methods work but this one has 'ALWAYS' worked for me . sorry for the length of my reply . a throw-back to my days instructing young acft. mechs. . good luck .

 

Yes, still hydraulic roller lifters. The only thing used in the entire engine besides the heads and the block are the connecting rods, pistons, and valves. My checkbook is evidence of that. Guess you're still instructing because I work for RR! I will give it a shot and report back.

 

Ran a compression test last night. All 8 cylinders are at 150 psi each. I will run the valves this weekend.

 

When working on a hydraulic cam you're actually setting Lifter Preload, NOT valve lash. The term Valve Lash is reserved for mechanical/solid lifter cams (both flat tappet AND roller versions). If you're running a mechanical/solid lifter cam the cam card will tell you what feeler gauge (thickness) to use. A feeler gauge isn't used on a hydraulic cam though.

As already mentioned, there are several different ways to adjust lifter preload. And, yes, all of them will work, but only if done correctly.

Guys tend to have their preference and your Dad seems to have his. The main difference is one method is easier and less likely to cause an error, but bottom line is it's a personal preference thing.

I started out, decades ago, setting mine using the running method. I used the clips, too, in order to keep oil from shooting everywhere. As time passed I began using the IC/EO (Intake Closing/Exhaust Opening) method primarily because the running method doesn't work on solid/mechanical roller cams. Those cams call for a certain clearance be set NOT preload.

No matter which method you choose, the most important part is making absolutely sure the lifter is riding on the base circle/heel of the cam lobe to find what's called ZERO lash.

I'd need more of an explanation of your Dad's recommended use of a feeler gauge when working on a hydraulic cam. He obviously has something in mind, I just can't figure out what it is. Ask him for an explanation and post it here. I'd like to know what he has in mind.

So, yes, you can do it his way. Let te engine idle, then back off on the adjusting nut until you hear a clacking sound. The SLOLWLY tighten the nut until the clacking sound just disappears AND, from that point, turn the adjusting nut more. Guys using the running method believe that when the clacking stops, the lifter is on the cam lobe's base circle/heel.

Now, the amount (more) you turn the nut after finding ZERO lash is another one of those "personal preference" things. Recommendations are all over the map on that one. GM says "One Full Turn" in some of their manuals but in other manuals it says "One Full Turn +/- 1/4 Turn". Then you have guys saying less than 1/4 turn; others say 1/2 turn, on and on.

I prefer 3/4 turn which gives me the quietest running valve train with no down-side.

Jake

 

I backed off 1/2 turn and have clacking. I took the car down the street and have no gain/loss in performance. The stumble is still there and getting worse before I started adjusting the lash.

The feeler gauge recommendation was if you couldn't hear the clatter, you could feel the tug on the gauge and listen for the load on the engine.

I am putting the 1/2 turn back in tomorrow morning. I am getting discouraged...........

 

When you backed off the 1/2 turn and heard the clacking that's because backing off created clearance between the pushrod and the lifter.

Next step would be to SLOWLY tighten down the nut until the clacking just ceases - goes away. That's ZERO lash. Remember, I'm using the word "CLACKING" because it's going to sound just like that - CLACKING. Not Clicking or tapping - CLACKING. The sound will be loud; loud enough to hear without any problem - you'll know it when you hear it.

Slowly tighten the nut until the CLACKING ceases. Once that happens it's time to set the preload.

Once the clacking has ceased (ZERO lash) an additional 1/2 turn (or whatever amount you decide to use) sets the preload. As I wrote earlier, that's when I tighten the adjusting nut 3/4 turn.

Back off until you hear CLACKING, SLOWLY tighten until CLACKING stops, set preload. That's all there is to it.

Jake

 

I was hoping that I would change the idle stumble with the adjustment. I haven't. I will follow your directions, but I have to try and inject a little humor otherwise I might just gouge my eyes out right now.

I think you told me I can't miss it - that means I will..............

 

[QUOTE=jwande;4713125]I was hoping that I would change the idle stumble with the adjustment. I haven't. I will follow your directions, but I have to try and inject a little humor otherwise I might just gouge my eyes out right now.

I think you told me I can't miss it - that means I will............../[QUOTE]

LOL, okay. just give it your best shot.

Jake

 

Alright, here it goes. I was testing the NEW tps that I put on a month ago. I measured at the closed throttle with the car not running, 4.44 volts. At WOT, I was reading 0.49 volts. Why is it reversed? Isn't the larger reading at WOT????? Nevertheless, I returned/exchanged the tps. It appears to have fixed the stumble issue. The performance isn't there, but I may need to do the "flash a chip and make it run better with the new setup" thingy. And I will need to take the valve lash out. At least the stumble seems to be gone!

 

Looks like you're half-way home. One problem solved; one to go.

Jake

 

Jake - Thanks. I may take a break and just drive it for a little bit. Enjoy some of the fruits of my labor. Congrats to you and your son. My brother was class of 1990. Very prestigious and quite an accomplishment. Not many people understand what it means to make it through. Your son may not know it, but anything life will throw at him will be less than what he conquered at West Point. I too am proud of my brother. He retired as a Captain.

 

Thanks for the congrats! I'll be sure to pass it along to Ryan, and I know the feeling of pride you have in your brother's accomplishments.

You're absolutely correct about "Not many people understand . . ." Many of his high school class mates didn't even have a clue about military academies. Not a clue on hard it is to just be accepted, not to mention the four years of both academic and physical training.

Some learned though when West Point hit the front page of Forbes Magazine as the #1 college in the United States, beating out Harvard.

BTW, I've got one of those too. My oldest daughter, Harvard Class of 2005, Electrical Engineering.

Good luck with the car.

Jake