Misfire

New to the forum have been going through a lot of older posts and haven't been able to figure out my problem. my wife has a 97 Tahoe with 140000 miles. About a month ago it started showing a random misfire code but couldn't really notice when driving it. Several months prior to this I had installed new plugs wires cap and rotor with no issues. First thing I did was pull the plugs every one looked great. Ran some fuel cleaner through it with no change. Tested the fuel pressure and it was only running at 48 to 50 psi at idle so I replaced the pump. Still had a random misfire and showed eventually showed a crank cam no correlation code. Distributor gear is good and distributor is set properly. Replaced both cam and crank sensor and the correlation code went away but still have a misfire. Pops through the exhaust at idle and idle very rough. Runs well when on the gas to accelerate but at cruising speed starts to misfire again. Does anybody have any ideas what could cause this?

maybe check for a intake leak, some one else had the exact same problem just the other day, did basically that same steps you have then took it in for a diagnostic and was told it was a intake gasket leak, i wouldn't just take it for granted that that's what it is but it is something to check out, you can use starting fluid around the edges the gasket and listen for a change in idle.

Doubeleive said:

maybe check for a intake leak, some one else had the exact same problem just the other day, did basically that same steps you have then took it in for a diagnostic and was told it was a intake gasket leak, i wouldn't just take it for granted that that's what it is but it is something to check out, you can use starting fluid around the edges the gasket and listen for a change in idle.

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Thanks. I checked for vacuum leaks and used some starting fluid around the throttle body looking for leaks but nothing near the intake gaskets and plenum I'll check it out and post back

Still running the factory spider injection? If you cannot find any intake leaks it may be time to investigate...

Any way to test the spider injection without pulling the upper intake?

Not really. All you would do is inject excess fuel into the cylinder, possibly washing them out. In addition, you would not be able to check the spray pattern of the injectors. Look at it this way, you could do the intake gaskets and rule that out at the same time...

Checked for intake gasket leaks after work and everything looks good their. It is sounding more and more like it's the spider injection but before I go and replace it does anyone have anything else i should check out?

Pull the air intake off. At the rear of the spider injection there is a fuel pressure regulator. Inside is a rubber diaphram that regulates the pressure via engine vacuum. These diaphrams can rip not allowing proper control of the fuel pressure. I believe in order to access it you will have to pull the upper intake manifold. I may be misremembering this as it has been a while since I have pulled an intake on one of these. Either way, once you have access pull the vacuum line off of the nipple and check for fuel dripping out and/or a strong fuel smell. Either one is a sign of a failed regulator. If you do not see fuel or smell it then use a hand held vaccum pump to pull a vaccum on the regulator. If it leaks down at all then the regulator is at fault. If not, then time to test the injectors.
Good luck.

MeNmyHoe said:

Pull the air intake off. At the rear of the spider injection there is a fuel pressure regulator. Inside is a rubber diaphram that regulates the pressure via engine vacuum. These diaphrams can rip not allowing proper control of the fuel pressure. I believe in order to access it you will have to pull the upper intake manifold. I may be misremembering this as it has been a while since I have pulled an intake on one of these. Either way, once you have access pull the vacuum line off of the nipple and check for fuel dripping out and/or a strong fuel smell. Either one is a sign of a failed regulator. If you do not see fuel or smell it then use a hand held vaccum pump to pull a vaccum on the regulator. If it leaks down at all then the regulator is at fault. If not, then time to test the injectors.
Good luck.

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Thank you . I have a mpfi set up on the way 2 and 4 are getting excess fuel

That should clear up your issues. Might as well do the lower intake manifold gaskets and all that while you are there. Insurance against future issues.