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Stock VP 5L running a bit rich

Robert Peperz

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Hi all,

Just working on getting my VP SS roadworthy, but while having a bit of chubby inducing rev ups I've noticed there's a lot of unburnt fuel coming out the tail pipe and from the smell you can tell it's running rich.
As far as I know the car is still stock asides from extractors, that being said a previous owner has definitely tried to do work to it and they have definitely shown that they were mechanically incompetent so they could've screwed around with something and caused it.
Just wondering if anyone knows how I'd go about tuning the 304s? Or if there is a common problem that would lead to it running rich?

Any assistance would be appreciated
 

EYY

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There are a couple of things that can make it smell rich without actually being rich. Main ones are hollowed cat and aftermarket cam.

Assuming it’s all stock and cat is in good condition (keep in mind cat will only really do it’s thing when it’s properly warmed up), then there are a few things you can start with.

1)Oxygen sensor
2)leaking fuel pressure regulator (pull vac hose off reg to confirm)
3)coolant temp sensor
4)map sensor (less likely - would run like poorly and wouldn’t respond well under load).
5) pull the cover off the ecu and see whether memcal looks stock - may be a cheap aftermarket tune causing it to run rich

It’s also worth checking that timing is set correctly at 10 deg btdc in diagnostic mode before doing anything else.
 

MikeC

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Check the wires are connected to the ECU coolant sensor. In the block behind and below the throttle butterfly there's 2 temperature sensors. The one on the right with a clipped square connector feeds the ECU, the one on the left with the single green wire feeds the dash gauge.
 

Robert Peperz

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Thanks guys for the info, I've gotta do some work to the exhaust anyway so might check the cat to make sure it still exists, if it does I might try working through those points cause I'm leaving behind streaks of fuel on the ground (Have smelt it it is fuel).
So does tuning a 304 generally require getting a new memcal? (I've only had experience tuning carburetors never done anything with EFI)
 

EYY

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Thanks guys for the info, I've gotta do some work to the exhaust anyway so might check the cat to make sure it still exists, if it does I might try working through those points cause I'm leaving behind streaks of fuel on the ground (Have smelt it it is fuel).
So does tuning a 304 generally require getting a new memcal? (I've only had experience tuning carburetors never done anything with EFI)
If it's dropping fuel, look between the tank and the diff and make sure the hose clamps for the high pressure and return fuel lines are tight. They very commonly come loose, especially when the incorrect clamps have been used and the rubber hose perishes.

Tuning isn't so straight forward. The easiest way to tune them is to purchase a mail order tune. While you may not get the max performance from a mail order tune, it'll generally be pretty close. And with the low compression of these engines from factory I they're fairly forgiving of poor tuning.

If you're willing to learn to tune and outlay some cash - approx $300-350 for aldl cable and nvram, plus the cost of a decent wideband o2 sensor. You'd need to invest a lot of time to learn, so it isn't for everybody. You can read about it on the pcmhacking forum.
 
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