[JLMounce]

For a couple of weeks now I've been noticing that the engine in my 69 bird has not been running the same. I wouldn't say it was running poorly, just not the same.

The idle quality has become rough compared to previously and I've also noticed that at times the clatter that I've always had in the valvetrain will increase, then subside.

At certain times there is a hard thudding gate to the idle as well that you can feel in the car. Almost like one or two cylinders are pumping much harder than the rest.

Yesterday, my suspicions of something going south were confirmed. Had the car out with my My in-laws and my parents and their corvettes. While horsing around a bit, The engine refused to rev past 4000 rpm. I don't let engines do things they don't want to do so I immediately got out of it at that point.

Curiosity got the better of me however and I did a quick bit of testing. Fired up the AFR guage on the FiTech handheld and wanted to verify I wasn't leaning out. At least via this observation method, my fueling is accurate around 12.6:1 at WOT. If I stay in it however I'll get a backfire through the throttle body.

If I nail the throttle the engine stutters badly and then will accelerate. If I roll into the throttle easily it will accelerate, at least up to about 4000 rpm where it falls on it's face. Overall power is down as well and the engine does not sound happy at all beyond 3500 rpm.

I need to put a fuel pressure gauge on the system to verify for sure this isn't fuel related, but I'm about 90% sure I can rule that out.

What I'm currently thinking is that I've got a valvespring or lifter issue, possibly both.

The top end was put into service in mid 2015 and I'd say I have around 30K on it. KRE D-ports with whatever springs Kauffman installed. The cam is a comp roller at 232/238 112+4. It uses the following XFI lobes.

Intake - 13081B
Exhuast - 13141B

.543 and .538 gross lift with 1.5 rockers

I know these lobes are pretty aggressive and were originally designed with intended use of a beehive spring. I have dual cylindrical springs in my setup.

I'm hopeful this can be a spring and lifter change without removing the heads, but I need to get in and do some diagnostics this week.

I'm not sure if weak valve springs will show up on a compression test, but that is first on the list as well as visual inspection of the current valve springs. From there I'll take the intake and valley pan off and start inspecting the lifters and the cam itself.

I'd really love to hear from more of you on anything I might not be thinking about here. I had this engine out of the car last year, inspected everything and visually it was all gravy. Bearings looked fantastic etc. I'm pretty bummed that it's giving me fits currently.

[steve25]

1 8 4 3 6 5 7 2.
Double check that your firing order is right.
This is the first thing that comes into my mind after reading your description of the issue.
Cylinders firing when there not supposed to will limit rpm greatly.

Pop the Dizzy cap off and look for signs of arcing or a busted rotor tip.

Next is that with the 30k on the heads they may have a intake seat or 2 that is moving around and is loosing seal.
This would also explain your backfiring.

The above if taking place is very bad because it’s likely to snap a valve head off on you.

Have you had to readjust your idle speed lately to pick it back up?
That would indicate retarded timing and maybe enough to cause backfiring.

I would put weak valve springs last on the list of things to check since you say the motor is even not smooth at idle anymore.

[JLMounce]

Timing was recently checked late last year after I replaced the harmonic balancer. It's computer controlled with a locked out distributor. It uses an adjustable rotor that was also locked down and additionally loctite added. But it doesn't hurt to check those items again.

Besides removing the heads, is it possible to determine if a valve seat is moving?

I have not had to re-adjust my idle. However it's important to note that the system uses an IAC valve, so changes in idle are compensated for by opening or closing that valve as needed. This may hide any timing abnormalities that you may notice with a carburetor. I have not noticed a change in IAC count behavior, but admittedly it's also not something I track closely.

[Half-Inch Stud]

Aside from "old gasoline", i suspect a wore Cam EXH lobe. But maybe a rotor-phasing needs verified. The rare-but-possible is a shorted Sparkplug.

[JLMounce]

Fuel in the tank is 2 weeks old. I'm going to check that the adjustable rotor has not moved when I check the timing system in general.

I do want to reiterate, this engine has functioned without issue in its current state for almost 10 years. I change the oil every year, put fuel in it and drive. These symptoms aren't from anything like a new build, recent tune-up, cam change etc. The longest the car has gone without being driven over the past year is about 4 weeks.

[steve25]

KD tools makes wallet friendly somewhat L shaped valve spring compressor bar that’s easy to use to remove your valve springs if you need to go that route.

If you use it just make a soda can sleeve to go over the threads of the rocker stud so you do not chew up the threads with the movement of the bar.

[JLMounce]

How long do valve springs typically last? Obviously this isn't anywhere near an OEM spec cam, so I wouldn't believe that I could get 100K out of them. But what kind of life expectancy should I be looking at in a moderate street build at around .550 lift on aggressive hydraulic roller lobes?

[PunchT37]

Maybe a valve or two hanging up in the guide? Seen it before.

[geeteeohguy]

I would throw it on an ocilloscope and look at the ignition pattern. Very possibly an ignition issue that will show up on the screen easily. Why tear an engine down if it's an open wire or bad plug, cap, or rotor?

[65madgoat]

I feel ignition/fitech electrical issue is your problem.....good luck.

Also I have seen a fuel supply issue cause fitech to then dump more fuel to maintain afr and cause issue you are having. What are you using for fuel delivery?

[JLMounce]

Originally Posted by 65madgoat

I feel ignition/fitech electrical issue is your problem.....good luck.

Also I have seen a fuel supply issue cause fitech to then dump more fuel to maintain afr and cause issue you are having. What are you using for fuel delivery?

Anything is possible, the system is 10 years old.

Fuel delivery is a tanks inc fuel tank with their GPA 4 (walbro 255) in-tank pump. -8 supply and return lines.

[Dragncar]

Hyd roller ? With the issues those have had over the years I would pull the valve covers and start looking around. Then pull the intake and inspect every lifter and look at all the lobes I could see.
It seems like those are always on borrowed time.

[65madgoat]

I had that setup...fuel pump cooked, had same issue you are experiencing. Twice.

Learned after 2 pump fails and ditched it for new GM AC Delco(LS style - cough cough) in tank pump with no return line.

[JLMounce]

Originally Posted by Dragncar

Hyd roller ? With the issues those have had over the years I would pull the valve covers and start looking around. Then pull the intake and inspect every lifter and look at all the lobes I could see.
It seems like those are always on borrowed time.

It’s in the back of my head. I have the older Lunati lifters prior to the updates Morel did in 2021. I inspected them last in 2021.

Originally Posted by 65madgoat

I had that setup...fuel pump cooked, had same issue you are experiencing. Twice.

Learned after 2 pump fails and ditched it for new GM AC Delco(LS style - cough cough) in tank pump with no return line.

This is certainly possible. These components are a decade old and have seen significant use. Going to a pwm controlled pump with a single line would also simplify things as well.

[TedRamAirII]

I would pull the valve covers and check valve springs ASAP.

[Jay S]

I am curious what you find. Checking the fuel pressure than then potentially pulling the valve covers off and inspecting the valve springs sound like good next steps. Hopefully it is the easiest fix, which would be the fuel pump or pressure regulator won’t build enough pressure anymore.

If those things check out, the good AFR reading seems to point to something other than fuel???? The engine shuttering under light load with a high rpm backfire after those other things check out it is probably time look more on the spark control side.

With 1.5s and the lifters mentioned the valve springs probably are not getting all that much abuse, the 1.5s make the cam quite a bit less aggressive. Clattering lifters are hardest on the valve guides and then you typically expect extra oil use before it becomes bad enough to unseal a valve. If it wasn’t starting to use more oil my best guess it is not a mechanical issue, and that lifter noise variations you were heard could be coming more from something modulating how the engine was running.

[JLMounce]

Originally Posted by Jay S

I am curious what you find. Checking the fuel pressure than then potentially pulling the valve covers off and inspecting the valve springs sound like good next steps. Hopefully it is the easiest fix, which would be the fuel pump or pressure regulator won’t build enough pressure anymore.

If those things check out, the good AFR reading seems to point to something other than fuel???? The engine shuttering under light load with a high rpm backfire after those other things check out it is probably time look more on the spark control side.

With 1.5s and the lifters mentioned the valve springs probably are not getting all that much abuse, the 1.5s make the cam quite a bit less aggressive. Clattering lifters are hardest on the valve guides and then you typically expect extra oil use before it becomes bad enough to unseal a valve. If it wasn’t starting to use more oil my best guess it is not a mechanical issue, and that lifter noise variations you were heard could be coming more from something modulating how the engine was running.

I have a fuel pressure gauge and AN to NPT adapter that I'm going to plumb into the throttle body. I'll be able to see what the fuel pressure is doing and that will be a big tell to the whole situation.

I'll know more later this week as I'm able to get some time on the car, but I really don't suspect any timing issues. It starts right up and even under heavy load is fine until the engine simply noses over and won't rev.

But, I'm checking everything regardless. I'm waiting for a call back from KRE on what parts the heads were built with. I'm also going to check with comp to see what they recommend in a beehive spring.

I also have a line on a set of very lightly used Johnson hydraulic rollers. Only about 30 minutes run time on them, but the engine did have a cam bearing failure, so I would need to clean them. I'm actually half tempted to go through the entire deal. New fuel pump, new springs, lifters etc. 10 years of being beat on, it might just be time on these components.

[Formulajones]

One thing about these EFI units when fuel pressure issues arise, you can't really tell just by the afr gauge.
These systems will compensate for a weak fuel pump and continue to add more fuel to meet your target afr. You need to look at a datalog to see it. Or look in the tune. You'll see things like the learn table going nuts in the wot areas adding a ton of fuel and it will continue to add fuel up to where ever you have your compensation limits set. Once you reach that threshold it will stop adding fuel and if it's not enough then of course the nose over sensation or lack of rpm.
These EFI units are good at masking fuel issues depending on how you have the tune set up

[steve25]

If your hearing no valvetrain noise at hot idle I can't see any darn reason for suspecting worn Hydro roller lifters.
I have heard of conical springs breaking though.

[JLMounce]

Originally Posted by Formulajones

One thing about these EFI units when fuel pressure issues arise, you can't really tell just by the afr gauge.
These systems will compensate for a weak fuel pump and continue to add more fuel to meet your target afr. You need to look at a datalog to see it. Or look in the tune. You'll see things like the learn table going nuts in the wot areas adding a ton of fuel and it will continue to add fuel up to where ever you have your compensation limits set. Once you reach that threshold it will stop adding fuel and if it's not enough then of course the nose over sensation or lack of rpm.
These EFI units are good at masking fuel issues depending on how you have the tune set up

Yes, that's why I'm getting a gauge on it. I also need to run a datalog, but I'm a bit fearful of doing so incase something more major is occurring. I did notice last week that the system was struggling to maintain AFR at idle for a couple minutes. It would hunt to mid 15's where it's usually rock steady around 14.3. It cleared up after though. This could be a symptom that I was overlooking.

Originally Posted by steve25

If your hearing no valvetrain noise at hot idle I can't see any darn reason for suspecting worn Hydro roller lifters.
I have heard of conical springs breaking though.

The valvetrain I have in the engine has always been very noisy. I've long attributed it to the aggressive cam lobes, the fact that the engine doesn't produce a great deal of warm idle oil pressure (typically around 15psi) and the Lunati lifters which are known to be noisy. What I have started noticing however is that they have started to clack more recently and even off-idle. Once oil pressure comes up off idle, they tend to quiet back down and you hear the HS roller rocker's sewing noise instead.