1991 Chevy Camaro 3.1 V6 Rough Idle

Maintenance/Repairs
21

That info is wrong. 145 to 160 will run but it’s on the way downhill. The general rule of thumb is 20 X the compression ratio at sea level with a good engine… This will vary based on barometric pressure, humidity, hot/cold air, altitude, etc.

A 120 PSI is only good for an old VW air cooled Beetle and that’s only because they are about 6 to 1 compression ratio. I’m also familiar with various manuals which state that a 140 is good, etc and that is also wrong. Over the decades I’ve probably done thousands of compression tests on everything under the sun from cars to motorcycles to aircraft so I kind of know the trends.

Another example of a manual being wrong is Chilton’s stating that a 3.8 GM engine has good oil pressure if it has 18 PSI at 1800 RPM. That is flat bogus.

22

That was last year. Check the IAC again.

23

Thanks for the info. I havent run too many compression tests and trying to find what good values should be has been a bit difficult. I’m hoping this is matter of the engine being cold giving bad info as wqell as a bad gauge and these fuel injectors are the majority of the problem. then again if worse comes to worst, time to start looking for a 350 lol.

24

If I’m not mistaken, the engine should be warmed up, and you’re supposed to make sure the throttle is fully open when doing the compression test

I’d do another compression test, warmed up and throttle fully open . . . please post the results

If you like, do that wet compression test . . . if the numbers go up dramatically, the bottom end isn’t sealing properly

If they don’t rise, the problems are most likely top end . . . perhaps the engine needs a valve job

Did you replace that fuel pressure regulator you mentioned . . . I would, because it’s typically not that big of a deal, and it plays a huge role, in regards to running rich or lean. It might very well have a blown diaphragm, given it’s close to 30yrs old

25

I’m pretty sure full throttle is only needed to prevent the injectors from spraying gas everywhere which i fixed by just unplugging the main connector. yea the engine was supposed to be warm i should redo my tests.
Regarding the regulator, no i did not replace it because the plastic vacuum line blew, not necessarily the regulator, When I pull the plenum back out toddo the injectors, I’ll test the regulator.

26

I would just replace it . . . don’t assume the broken plastic vacuum line was the only problem

It seems crazy to remove the plenum, replace all the injectors, the vacuum line and NOT also replace the regulator at the same time . . .

You’ll sleep better at night

27

I do like to sleep at night whenever possible. I found a regulator for 33$ on rock auto and should arrive the same day as my new injectors.

1 Like
28

Vacuum gauges are cheap, I think you would be much better served by hooking a vacuum gauge up before spending beaucoup money. Fifteen bucks at Harbor Freight and it will work fine.

29

NO ! Throttle wide open is to allow for the maximum volume of air to be drawn into the cylinder.

2 Likes
30

Good to know. Honestly even if we find the worst with this car. I’m learning a ton of stuff I didn’t know about these kinds of tests.

31

Next time I’m up at my local HF, I’ll grab one. I do see they are literally 15$ and a good inexpensive tool to have.

32

It looks like we may have a winner. We replaced the Injectors and regulator today. The old injectors lookedl ike they were mismatched and all of them were missing the lower orings that go into the engine. Got all of that back together and after a bit of priming she started running way better. The exhaust smells more like exhaust and less like bumper boats and hardly any smoke out of her We’re going to run some seafoam through her because I’m assuming there’s a ton of carbon build up from how poor it’s been running.

I’ll update if things change. In the meantime, Thank you everyone who contributed. I’ve learned a ton about things to check in these kinds of scenarios.

7 Likes
33

You mentioned the oil smelled of gasoline. Have you changed it? If not, do so before running the engine.

2 Likes
34

I completely forgot I mentioned that, thanks for bringing that up, We’ll do that before running her again.

35

A local parts place may have a loaner vacuum gauge. The way my nearby O’Reilly’s does it is you pay for the tool, then are refunded when you return it on time.

36

Those injector o rings are a pretty common problem on older cars, I had to replace the ones on my '83 GTI years ago.

1 Like
37

Congratulations!

:+1:

we knew you could do it :smile_cat:

2 Likes
38

Good work… You got some useful advice for sure…and that guy who suggested to look into injectors must know what he is talking about. @Mustangman is good that way.

Glad you got it sorted out. Feels good doesn’t it ?

I’m still trying to picture that funky intake plenum of the 3.1 … it had an X shape on top of it, if I recall. However, that was a long long time ago, in a galaxy far far away, when the guy who looks like me had a lot more brain cells. I still think it had an X shape…allow me my delusions…your day will go a lot smoother.

2 Likes
39

My first GM 60 degree V6 had a carb… my last had fuel injection but blew up when coolant rushed into the engine from an intake leak… I think. It was done anyway.

Never actually had to work on the FI on those engines!

40

With gasoline diluted motor oil being changed you need to revisit that compression issue and pray that it’s not the diluted oil doing this or excessive wear caused by that diluted oil.

With fresh motor oil and if the compression numbers are still low the engine still has a problem.