then your cam maybe shot. also look for a possible bent pushrod. i would pull them and inspect. then readjust and try again.
175 lbs pressure in #2 cyl.
Thread Starter
Advanced
Joined: Jun 2004
Posts: 76
Likes: 0
From: St. Augustine FL
175 lbs pressure in #2 cyl.
Hey all,
I have still been trying to get final diagnosis on my miss that has plagued me for some time.
Yesterday, ran a pulse check on my fuel injectors, all is well. But my #2 cylinder doesn't fire (removed fuel injector plug while running, and no drop in idle). So we ran compression test on cyl #2 and after 5 cranks she reads 175 lbs! That's got to be too much! What is stock? on a 93 LT1?
Though it was a bad exhaust valve (maybe stuck open) but did the dollar bill test on the muffler outlet and the bill was not sucked in. So now we are thinking a stock "closed" exhaust valve, hence the high build-up of pressure.
Can you guys please help? Confirm or denounce?
I have still been trying to get final diagnosis on my miss that has plagued me for some time.
Yesterday, ran a pulse check on my fuel injectors, all is well. But my #2 cylinder doesn't fire (removed fuel injector plug while running, and no drop in idle). So we ran compression test on cyl #2 and after 5 cranks she reads 175 lbs! That's got to be too much! What is stock? on a 93 LT1?
Though it was a bad exhaust valve (maybe stuck open) but did the dollar bill test on the muffler outlet and the bill was not sucked in. So now we are thinking a stock "closed" exhaust valve, hence the high build-up of pressure.
Can you guys please help? Confirm or denounce?
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Unless it is drastically low, a compression test on a single cylinder isn't worth much. The results of a compression test are to be compared, cylinder to cylinder. Check ALL the cylinders. If there are any suspicions, do a cylinder leakage test on ALL the cylinders. Your 175#, by itself sounds about right. My 160,000 mile Crossfire ranges between 165 and 175 pounds across all 8 cylinders.
RACE ON!!!
RACE ON!!!
Thread Starter
Advanced
Joined: Jun 2004
Posts: 76
Likes: 0
From: St. Augustine FL
Yup, there's spark when we take the plug out and start the car. It just doesn't want to fire inside the cylinder. It's getting fuel, pulse, and spark (at least outside the cylinder). The only thing I can't figure out it the cylinder seems to turn a plug black in a matter of days, but the plug keeps firing
Thread Starter
Advanced
Joined: Jun 2004
Posts: 76
Likes: 0
From: St. Augustine FL
Yeah, the next thing we were going to do was to pull the valve cover and check the exhaust valves and such. I was just hoping that I didn't need to pull the head. At least the side with the 'issue' is the passenger, which appears much easier..
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Unplugging an injector isn't going to tell you anything as the IAC will maintain idle and as pointed out, a compression check on one cylinder doesn't tell you very much. 175 is in the ballpark and you should at least remove #4 when you check it. You could also squirt some oil in it, but without knowing what all the other cylinders read, I don't think that's going to tell you anything either.
Your problem could easily be a bad plug wire. Did you swap it out for a good one? It could also be a leaking injector, code 45 set? Fuel pressure holding? Does the plug smell like gas? The valve seals could be weak too or the intake manifold gasket might be sucking oil. What's vacuum?
Your problem could easily be a bad plug wire. Did you swap it out for a good one? It could also be a leaking injector, code 45 set? Fuel pressure holding? Does the plug smell like gas? The valve seals could be weak too or the intake manifold gasket might be sucking oil. What's vacuum?
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Hmmmm! Have you tried removing the plug wire while engine is running? see if that makes a difference, becareful though it does bite-use insulated pliers. If you had a valve stuck open your compression would be consantly low. The plug turning black sounds like oil. Did you squirt a little oil in the cylinder to see if compression rises? If it does it's bad rings. The 175 sounds ok to me-but the real test is to read them all-they should be within 10 percent of one another. I'm thinking a bad plug or wire leading to a weak spark. Good Luck 
Drifting
Joined: Nov 2002
Posts: 1,593
Likes: 0
From: Mobile AL
St. Jude Donor '05
In my experience, 175 is a tad low, but not enough to cause misfire. It may be a flat spot on the cam - not letting intake and/or exhaust open at all. Pull the valve cover and see if they move.
Thread Starter
Advanced
Joined: Jun 2004
Posts: 76
Likes: 0
From: St. Augustine FL
I do read a code 45, yes. But also others, code 32.
32 = EGR sys Prob
64 = Right 02 sensor to lien
I have low BPW (ms) 17.3 , whatever that means
And QDM 2 fault
and WDM 3 fault.
It also said (the diagnostic) that I had a #2 injector fault. But I changed the injector and the exact same problem persists.
The IAC comment, where I wouldn't notice a difference, well, the thing is, I do have a difference on all other injectors. With the car running, I can go one injector at a time, remove the wire harness for it, and the idle will drop down. But when I remove the #2 injector harness, there's no change at all.
I have been told to check the plug wire (which would make me sick if was the cause), but I have yet to. The plug wires on there are not even a year old, so I figured they were ok. I will check, tis an easy one.
32 = EGR sys Prob
64 = Right 02 sensor to lien
I have low BPW (ms) 17.3 , whatever that means
And QDM 2 fault
and WDM 3 fault.
It also said (the diagnostic) that I had a #2 injector fault. But I changed the injector and the exact same problem persists.
The IAC comment, where I wouldn't notice a difference, well, the thing is, I do have a difference on all other injectors. With the car running, I can go one injector at a time, remove the wire harness for it, and the idle will drop down. But when I remove the #2 injector harness, there's no change at all.
I have been told to check the plug wire (which would make me sick if was the cause), but I have yet to. The plug wires on there are not even a year old, so I figured they were ok. I will check, tis an easy one.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Looks like the fault is in the injector circuit, not the injector. The cylinder isn't getting gas, that's why the rt. side O2 is lean. Engine tries to compensate and dumps fuel into the other injectors, giving it the 45. I don't know what the WMD is, but you need to fix the electronics and that should cure the miss.
Thread Starter
Advanced
Joined: Jun 2004
Posts: 76
Likes: 0
From: St. Augustine FL
Mentioning the injector circuit reminds me to ask another question regarding that: Are the injectors supposrted by a fuse/relay? Or do they read straight from the computer, any thought?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Injectors receive ignition power from the injector fuses, but are individually grounded or driven by the ECM. If a fuse was blown, a whole bank of injectors would be out. You only have #2 to concern yourself with. The problem is on the ECM side, which I think for #2 is green/black. The wire may be shorted which has shutdown the driver to protect the ECM or the ECM may be bad. If you have the shop manual, use the fuel system charts or Section 8A in part 2 of the Manual to find out how to diagnose it.
Thread Starter
Advanced
Joined: Jun 2004
Posts: 76
Likes: 0
From: St. Augustine FL
Thanks for the info. I don't have the shop manual, but I have access to one. As far as the actual injector, it does have power, shown by the test light, but I have no idea if the pulse is accurate.
Advanced
Joined: Jul 2004
Posts: 80
Likes: 0
FWIW, I kept fouling my #7 plug in <10 miles and couldn't figure why until I discovered, thanks to the folks on this Forum, that #1, #3, and #5 injectors were shorted! The O2 sensor saw a bulk lean exhaust and richened the entire left bank, but with only #7 working it soaked the plug.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
If you can't get the manual, retest the harness by checking for voltage on the ECM side. There shouldn't be any on a sequential fire. So, with the ignition on, a test light to ground from the ECM side of the harness shouldn't light up. If it does, the wire to the ECM is probably shorted to voltage. Check to see if the terminals are touching inside of the connector. Before you tear into the harness, you should check continuity from the injector to the ECM. You can also repeat the test with the harness unplugged at the ECM, and then with the ignition on, a test light from the #2 ECM injector terminal to ground shouldn't light up. If it does, the PCM is bad, but with the driver shut down, I doubt you'll get this result - it's more probable that you have a short to voltage, or the wire is open.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Forgot to mention, after making repairs, clear all the codes by disconnecting the battery. The driver should work once the circuit is good, but some PCM's need to rebooted - so to speak - before they function correctly.