High RPM Bogging/Backfire Between Shifts

[98snakehorse]

My 98gt has been running great this season however recently I noticed some bogging and backfire issues which seem to be becoming progressively worse. I took the car out for a spin tonight and got on it down an off ramp and noticed everytime I went to shift in high rpm the car would backfire/studder and bog really bad into the next gear.

Car has a complete PI engine brand new plugs/new fuel filter, red monster cop conversion (which has worked great), Brand new upstream O2 sensors. I suspected that the fuel pump may be going out as it had seemed a bit too noisy at times. I'm sure it's still the factory one 145ks on it.

I've order a new fuel pump (walbro 255), We'll see if that clears it up; however this has me stumped as it has been running hard as hell for me tell now.

 

[Ferocious]

Do you have a way to check the AF ratio? The backfire i'd assume is from running rich. If a new fuel pump does nothing, maybe check the injectors.

 

[lutter94]

Doesn't hurt to seafoam it (fuel tank and vacuum), if you've never done it.

 

[98snakehorse]

Injectors are sadly high mileage aswell. Its one of those things where I don't want to throw money at the wrong things so was hoping someone had similar issues as me. My guess is one of the injectors is failing, a coil pack could be going bad too. I suppose I can find another set of 19lb injectors cheap as I think that's what the orange ones are. I have some extra coil packs I can try swapping out. Ahhh I hate fighting these gremlins!!

 

[96blak54]

Unplug maf sensor and then go drive it hard. Report findings

 

[D3VST8R96GT]

Spark plug gap?

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[98snakehorse]

Spark plug gap?

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Spark plug gap is factory 0.052 which I double checked before I installed. I ended up disconnecting the negative terminal on the battery and resetting the ecu. Also swapped out a couple of coil packs and it seems to have cleared it right up. Pulls hard all the way up to redline.

 

[Musturd]

When my 96 did this it was because of a crack at the thermostat housing on the plastic intake and water was getting into the spark plug boot and causing a misfire it's just a thought pull ur spark plug wires out and check for moisture those plastic intakes are prone to cracking

 

[98snakehorse]

When my 96 did this it was because of a crack at the thermostat housing on the plastic intake and water was getting into the spark plug boot and causing a misfire it's just a thought pull ur spark plug wires out and check for moisture those plastic intakes are prone to cracking

My thermostat housing is the aluminum one and its doing good no leaks there. I also dont have spark plug wires as I'm COP. I'm thinking I got it fixed but just to be sure since my fuel tank is out right now because I'm putting a walbro 255 in. I'm going to delete the PPRV on the new pump which should resolve any other chances of high rpm fast shift bogs.