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Discussion Starter · #1 · (Edited)
Hi everyone... I need some troubleshooting advice on this one...

I have a 1998 Camaro, 3.8 V6 automatic with 173k. No check engine light or codes. The car recently developed a kind of flooding issue that resulted in hard starts after sitting for a few hours and fuel getting in the oil. The analysis report stated 6.6% when I had it tested at 950 miles on the oil.

I replaced all 6 injectors, assuming at least one was leaking. When that didn’t fix it, I found that the fuel rail wasn’t holding pressure and that the vacuum line to the fuel pressure regulator smelled like gas when disconnected (no liquid fuel noticed). For good measure, I changed the fuel pressure regulator too, since I assumed the fuel smell indicated a leaky diaphragm. That didn’t solve the problem either.

First thing in the morning, the car starts fine. When I get in the car at lunchtime, 4-5 hours later, it cranks but doesn’t want to start unless I press the throttle while cranking. It doesn’t have to be more than 1/3 throttle to start it, but it fires right up when the pedal is pressed. Once running, there are no drivability issues. It never stalls, hesitates, or misfires. It just seems to either be leaking gas into the intake after shutting off the ignition or dumping too much fuel while running. It does it every time I drive it and let it sit for less than 6-8+ hours.

I haven’t checked fuel pressure because A) all or most pressure bleeds off after about an hour, and B) it runs and drives fine once it’s started.

But again, no codes are showing up. I tuned it up last year with AC Delco plugs and wires, but not the coils. I haven’t pulled any plugs yet (cuz they’re so much fun on this engine), but I would think that it would run rough or throw a code if one or more cylinders weren’t firing properly.

I’ve checked various threads on different sites and found similar issues but not quite what my car is doing. Do you guys have any ideas?


PS- I also replaced the IAC valve...no change. It just seems to be getting too much gas or leaking it in the intake. Fuel economy has predictably deteriorated too.
 

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Discussion Starter · #3 ·
I know this thread is 3 years old now, but I wanted to come back with some updates. My 1998 3.8 is still having the same apparent flooding problem, and I haven’t been able to zero in on the cause. Here is what I’ve been able to confirm over the last 3 years:

- I replaced the lower intake gaskets a year or two before this started, used the premium gaskets

- spark plugs and wires replaced around the same time as intake gaskets. Delco parts

- 2 coils with pitted terminals replaced with Delco

- cleaned MAF sensor and replaced K&N filter with a paper one

- replaced all injectors, confirmed not leaking under pressure.

- replaced fuel pressure regulator to be safe

- confirmed injectors not sticking open electronically with Noid light

- confirmed fuel pressure within spec

-replaced coolant temp sensor at front of intake, below throttle body area

- no codes at all throughout the history of this problem

- live stream scanner data has showed that everything is running within textbook-perfect parameters every time a mechanic or my friend with a scanner has looked at it

- black sooty tailpipe, exhaust smells rich (but not like raw gas)

- faint gas odor from evap canister area (this just started)

- misses at idle, especially when warm

- tried capping off the purge valve port on the intake to see if vacuum was leaking thru sticking valve—no change

- oil analysis showed 6.3% fuel (but 0 antifreeze)

- only starts easily first thing in the morning now. Rest of the day, you need to push the throttle to allow more air when cranking it over to get it to start. It will crank and crank without firing up until you give it a fair amount of throttle (this is a cable throttle) to let it get some more air. It never stalls or surges.

With no codes, I don’t know what to try next. I haven’t replaced the O2 sensors yet because the shop couldn’t get the upstream ones out without pulling the manifolds, but scanner data showed they appear to be working normally. I’m beginning to think it has to be a vacuum leak, but all hoses are good. No exhaust manifold leaks. EGR valve was clean when I removed it and reinstalled it with new gasket.

Based on the above, does anyone have any recommendations for what to check next?
 

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Discussion Starter · #4 ·
I’m not sure if it’s 100% yet, but I had the upstream O2 sensors replaced and it’s much better now. It’s still running rich cold, but seems to straighten out once warm. Here’s hoping…
 
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