'74 vette, 454, manual, with diverter valve issues

[Ronald S.]

I have a 1974 corvette with 454 engine and manual transmission. I had diverter valve problem. Installed new n.o.s. diverter still have same problem. Decided to gut out air pump instead of throwing good money for bad. Car misses but does not backfire .Can anyone help.

[Michael W.]

Re: '74 vette, 454, manual, with diverter valve issues

It's not your AIR system and probably never was. Possibly the EGR valve is stuck open.

[Ronald S.]

Re: '74 vette, 454, manual, with diverter valve issues

Thanks I have been told that both valves on the diverter are stuck in a closed position. What does the egr valve have to do with this? Because now instead of backfiring it misses when under load.

[Clem Z.]

Re: '74 vette, 454, manual, with diverter valve issues

Thanks I have been told that both valves on the diverter are stuck in a closed position. What does the egr valve have to do with this? Because now instead of backfiring it misses when under load.

check to make sure you do not have a worn cam lobe.

[Michael W.]

Re: '74 vette, 454, manual, with diverter valve issues

Thanks I have been told that both valves on the diverter are stuck in a closed position. What does the egr valve have to do with this? Because now instead of backfiring it misses when under load.

As far as I know there is only one valve in the diverter, not two. Are you referring to the check valves instead?

The EGR, if stuck open can cause the difficulties you describe.

[Ronald S.]

Re: '74 vette, 454, manual, with diverter valve issues

If it is a worn cam lobe, Are there any other issues that tells me it is a worn cam lobe. Oil pressure is very good.

[Ronald S.]

Re: '74 vette, 454, manual, with diverter valve issues

Sorry but i meant that both diverter valves were stuck in the closed position. How does the egr valve cause this problem?
.

[Clem Z.]

Re: '74 vette, 454, manual, with diverter valve issues

If it is a worn cam lobe, Are there any other issues that tells me it is a worn cam lobe. Oil pressure is very good.

the best way is to remover the rocker covers and check for rocker arm movement. the reason i suggested this is i have seen this in several 454 engines.

[Michael W.]

Re: '74 vette, 454, manual, with diverter valve issues

Sorry but i meant that both diverter valves were stuck in the closed position. How does the egr valve cause this problem?
.

No C3 Corvette has two AIR diverter valves. I again assume you mean the check valves located on the AIR manifolds, but again this would not cause the problems you're mentioning.

[Peter G.]

Re: '74 vette, 454, manual, with diverter valve issues

Ronald...I have a '73 LS4 4spd and ever since I have had the car the engine misses at high RPM. 5K it just misses with no backfire.

Is that what yours is doing? I have changed distributor rotor and cap. Replaced spark plug wires. Replaced and went with heavier rocker arm springs. The last thoughts everyone has is worn or flat cam lobes on the camshaft?

[Ronald S.]

Re: '74 vette, 454, manual, with diverter valve issues

Had new plug wires, plugs, rotor, distributor cap, and electronic ignition installed. Originally the housing to diverter valve was not hooked up. Epoxyed housing back into diverter valve. Car was backfiring. Found out diverter valve was bad. Then took the pulley and belt off the AIR pump and it ran great. Installed NOS diverter valve and new check valves. Car ran good for a while and now runs bad. Had AIR pump gutted and installed and reinstalled NOS diverter valve. Now car misses under load. A club member suggested a bad cam lobe. Haven't checked that out yet. Do you still have a diverter valve? Have you checked this out?

[Ronald S.]

Re: '74 vette, 454, manual, with diverter valve issues

Sorry for the confusion. What I meant by two diverter valves is as follows: The diverter valve on my car was stuck in the closed position. So I purchased and installed a second NOS diverter valve and new check valves. This one worked for a while and then apparently stopped working and stuck in the closed postion as well. This is what I meant by two diverter valves. I had two different ones. So with the second NOS diverter valve installed, I gutted the AIR pump and the car misses upon load. The plug wires, plugs, distributor cap, and electronic ignition have already been changed. Can't figure this out.

[Peter G.]

Re: '74 vette, 454, manual, with diverter valve issues

Why are you so sure it is the diverter valve on the A.I.R. System.

My car missed when I purchased it and it did NOT have any A.I.R. Systems parts on the engine as they had all been taken off for performance reasons. I found the complete working system and had it installed. The car ran the same...still missing at high RPM. So in my case the A.I.R. System had NO bearing on my engine miss.

[Ronald S.]

Re: '74 vette, 454, manual, with diverter valve issues

The problem of the car not running right started when I started replacing the diverter valve. Even though I gutted the air pump now the car misses but does not backfire.I was told by one person that it might be a worn cam lobe. Does your corvette make any loud valve noise?

[Peter G.]

Re: '74 vette, 454, manual, with diverter valve issues

Ronald...no sounds that I can hear. Normal bearing noise from air pump, water pump etc.

I have found and put many many missing engine parts on my car since I purchased it to get it to NCRS Top Flight and fortunately none of the parts changed any of the running of the engine.

Like I previously mentioned I have done everything I can think of the fix the missing at high RPM short of removing and checking the camshaft. Don't know if I will ever do that if I believe you must pull the engine from the body to remove the camshaft and as you know the LS4 is a BIG motor and then add all the options....it's a pretty busy place! I don't drive my Corvette to that high of RPMs anyway.