Hi all - first time poster long time reader here. Forgive the novel, I'm trying to be thorough about my issue. For those of you who prefer, there is a tl;dr at the bottom.

A little while back, my 94 convertible (LT1, automatic, bone stock) started having a missing issue. After some research on the forums, I began to think optispark. My initial thoughts were confirmed about a week later, when she wouldn't start and threw the dreaded code.

After replacing the opti, it ran great for about a week, then the loss of power came back/ low RPM misfire. Because it had 75,000 miles, and I hadn't done a tune up since I bought the car, I put in new plugs and wires. Again, it ran better for about a week.

This is where it got a little strange. Besides the misfire, it developed an intermittent hard start issue. When it started fine, it ran great for about 5 minutes, then went back to the misfire. Most of the time, however, it took a good 5-10 seconds of cranking to start, then ran poorly from the get-go. It also started bogging down at first during hard takeoffs. Like trying to start a stick in 2nd gear. I tested fuel pressure which wasn't bad, if a little low - 40PSI. I also cleaned the MAF sensor and throttle body (with different cleaners).

Now to the actual point...

Halloween morning (of course), I got in to make my morning coffee run and turned the key. It turned a few times, then BOOM!!! It sounded like a shotgun; loud enough to cause my wife to come running out of the house. I nearly had a code brown myself. The explosion was closely followed by what I can only describe as whiteish smoke seeping through the headlight covers and creeping out from the finder wells. When the smoke died down enough for me to feel safe opening the hood, I could immediately see where it was coming from. The valve cover gaskets on both sides were blown almost completely out (see the picture). A couple hours later, after the smoke cleared and out of sadistic curiosity, I turned the key. Lo and behold, after a couple cranks, it fired up. I didn't run it long - blown out valve cover gaskets, and all - but it seemed to run well when it was.

Troubleshooting:

I initially thought blow by from a bad ring or cracked piston, which would explain why it was running rough. However, compression test doesn't seem to suggest that:

Cyl 1 - 125
Cyl 2 - 130
Cyl 3 - 140
Cyl 4 - 130
Cyl 5 - 125
Cyl 6 - 130
Cyl 7 - 125
Cyl 8 - 130

There was quite a bit of carbon on the plugs for how new they are. I should also mention that it doesn't seem that the oil pan gasket was blown out, which seems strange given what happened.


tl;dr - car was misfiring and hard starting. Tried to start, heard an explosion, saw smoke, valve cover gaskets blown out.

Any help, thoughts, or suggestion are greatly appreciated!

Thank you!

 

Sure sounds as though fuel has accumulated in the crankcase, leading to a fuel vapor buildup that ignited. Pull the dipstick and see if the level is above the full mark and take a sniff to see whether the oil smells like gasoline. If you smell fuel in the oil, do not run the engine until you have resolved the source of the fault and changed the oil and filter. If you have fuel in the oil, check for one or more leaking injectors. Also check (or replace) the PCV valve.

Uniformity of compression readings suggests no problem with cylinder sealing.

Good luck with it. Let us know how this one turns out.

Live well,

SJW

 

think you have more than one problem. leaky injectors or fpr smell your oil for fuel. bad 02's and how was the compression test done looks low.

 

Thanks for the quick responses!

Quick update: I definitely have fuel in the oil...

The compression test was done using a harbor freight special. I was mostly looking for a bad cylinder. I wasn't worried about how accurate the readings were.

I hooked up my fuel pressure guage to test for leaking injectors as per another thread on here. Since I don't want to start it, I turned the key on, but didn't turn it over. The pressure immediately dropped as soon as the pump shut off.

I am out of both light and time today, but I will be doing more troubleshooting after work tomorrow.

 

pull the vacumme line of the fpr and smell and look for fuel there. might just be a ruptured diaphram.

 

Fuel in the oil, and fuel pressure that plummets as soon as you go key-off, strongly points toward leaking injector(s). Check for this next.

Live well,

SJW

 

but the fpr will do this too and only one of them.

 

Finally got a free weekend! And all of the parts I ordered arrived. So, here's the story:

Pulled the valve covers, and everything looked good! No valve work or head work! Since everything was ok, I put the new gaskets on the covers and put them back on.

Per everyone's posts, I thought the best (read cheapest) place to start would be the fuel pressure regulator. I replaced that - not hard at all on that LT1, btw - and retested the fuel pressure. It held!

I also replaced the PCV valve for good measure and changed the fuel saturated oil.

I turned the key, and she started almost instantly! Albeit, there was an obscene amount of smoke at first. Once it all burned off, everything seems fine, so far.

Thank you all for your help!

 

great change your oil now before you do damage!!!!!!!!! sorry missed that you did that great job.

 

nice work on the fix.

 

Thank you! It turned out much better than I thought it was going to!

Thanks again everybody for the input and help!!!!!