Cold engine startup

[Wht87T]

Sometimes when its cold it'll backfire on startup. Almost like a popping. The factory boost gauge will flare up to about 12-15psi during this "popping" Does anyone have a diagnosis? TIA

 

[blackbuick87]

Are you giving it gas when you crank it?

 

[Wht87T]

NO not at all.

 

[6=8]

I have a theory!

Wht87T:

My 87GN started doing this at about 130K miles (It is at 150,000 now, and no longer does this.)

During startup/cranking the motor... a Big POP, and the boost gauge would show the pressure! I believe this was a backfire caused by weak valve springs or leaking injectors. Possibly a combination of both. Once I started the car (The starter/engine sounds kind of funny after it popped like that), it would run really rough for a while, then after about a mile of driving, all would be well again.

It would only do this after sitting overnight, leading me to believe that even if an intake valve(s) were sticking open, there was some fuel that leaked from the injectors contributing to the backfire.

Before I replaced the valve springs, I ran a bottle of CD2 in the engine oil. I noticed that the frequency of this startup condition reduced almost immediatly, and only did it very rarely.

My car no longer does this, (I didn't do anything with the injectors) but I have replaced a timing chain and valve springs since then.

Would be interesting to know how many miles you have...

Hope this helps! Try running some "Frees sticky valves" additive in your oil for a while and see if it stops. Worked for me!

 

[Wht87T]

My motor has about 77k on it now. Your description of the problem sounds exactly like mine! I'll give the addative a whirl and see what happens. BTW, this happened last night, and the car was in front of the house for a week.

 

[6=8]

Did you get a chance to run any additives? After 2 days of driving, mine quit popping AND a noticable improvement in high RPM operation. After that, I knew it was time to replace the valve springs.

I am curious to know what type of oil you be runnin' too. I used to run penzoil... Not anymore!

 

[blackbuick87]

Could be fuel leaking from the injectors or oil getting past the valve seals. Be sure to post whether this helps your condition or not.

 

[Wht87T]

OBTW

The valve springs and lifters were replaced last yr. I had a lifter tap problem, so we also decided to change the springs.