Backfire (?) during cranking?

[BlackMetal]

I put the question mark because I don't know for a fact if that's what happens, I've never had a car backfire on me before so I don't know what it would sound like.

Sometimes when I try to start my GN (87, 32k miles, stock at the moment), I basically get "crankcrankPOOF", and the thing that bothers me the most about it is that the boost guage completely pegs out when the noise occurs and then goes right back to zero. I don't know what would happen after that if I kept cranking, because I always turn the key off immediately when it occurs. Then I'll sit there for a few seconds, put the key back, and it starts up perfectly.

It doesn't sound like a loud bang or anything, but like I tried to describe it above, it's a fairly loud, but muffled POOF, muffled in the sense that I guess I'm hearing something under the hood in the engine compartment.

It doesn't really happen in any specific situation. At first it seemed like it was only when I left it in the garage over the weekend and went to start it on Monday, but since then I've had it happen after sitting for two days, one day, a few hours, just about any time frame, and no correlation to weather or temperature either.

Is this a common problem or something serious? I didn't search the forums because I figure looking up "backfire" could lead to 300 different problems.

Thanks for any help, I hope it's not too bad. :frown:

I'd take a video of it if I could, but of course every time I take my camera, it doesn't happen.

 

[gmpower6]

It could be a leaking injecter? I had that same thing with my 86t-type. Only when it got colder outside.

Sean

 

[vicious6]

The car is popping back through the intake. That is what causes the boost gauge to peg when this happens. I have had several TRs do this at one time or the other. If the car is running good otherwise, I really would not worry about it. As to what causes it, I really don't know. One would think maybe a slight timing offset, but I have never had this lead to a serious problem. I think it is just a hiccup so to speak with these cars.

 

[Welby]

Mine started doing the exact same thing a few months back. I got some 009 injectors from someone and after putting them in, it's never done it since. So you might have a leaky injector, like gmpower6 said.

 

[jpratt]

I had Casper wuick start cam sensor module in place and this will cause the backfire. On the other hand if it does not back fire then it started really quick. I got tired of the backfire no starts so I removed the quickstart module and it starts fine, so the module is now in the glovebox incase the cam sensor goes out.

 

[S10xGN]

Cam sensor is slightly out of adjustment, been there and done that.

 

[Steve V]

Mine does it too. If the cam sensor is outta spec which way and how much does it need to turn?

 

[BlackMetal]

Alright, well a backfire once in a while doesn't bother me that much, I mainly wanted to know about my boost guage maxing out.

I plan on getting Green Stripe injectors soon, so we'll see if that solves the problem. As far as the cam sensor, how can I test it and what reading am I looking for?

 

[salvageV6]

Here is one method.

I believe there are three methods on that site.

http://www.gnttype.org/techarea/ecmsensors/addcam.html