Take the 2-minute tour ×
Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

The car is a 1998 Oldsmobile Intrigue with 3.8L V6 engine (3800 Series). I've been doing my research and due diligence, but please understand I'm very inexperienced with automobiles.

I went to Autozone and the reading I got from the OBD II tool was a P0171 error code. A lean or rich condition on Bank 1. First, I don't know where Bank 1 is. I have a feeling it's a cracked intake-manifold, an intake-manifold gasket leak, or both. But let's assume I have no clue where the vacuum leak is coming from. And I don't want to use a carb cleaner -- I read that I could cause a fire and I don't think I'm experienced enough to use something like that. I'd prefer to err on the side of caution.

I've seen on youtube a long-time mechanic who uses a cigar as a cheap alternative to a smoke test machine. But I'm not sure if something like that could be used if you have no idea where the leak is coming from.

So I ask those who are far, far more experienced than me. What ares some methods I can use if I have a vacuum leak, but I literally don't have a clue where it could be?

Thank you.

share|improve this question

3 Answers 3

Bank 1 on your 3800 Series II Engine would be the set of cylinders that is closer to the front bumper of the vehicle (cylinders 1, 3, 5). Bank 2 (cylinders 2, 4, 6) would be against the firewall.

The Leak... Any vacuum-leak hunt shouldn't start without having a clear vacuum-hose diagram in-hand. There should be one on a placard inside the engine bay (possibly in the radiator mount area or the underside of the hood). Here's what it looks like.

If the vehicle does NOT have a supercharger then the vacuum system should look like this:

enter image description here

If the vehicle was equipted with a super charger then it should resemble the following:

enter image description here

Use this map to trace every vacuum line. Even if you cannot see the mall you should be able to feel them from start to finish to make sure they are connected at each end and do not feel fray'd or brittle or damaged in any way. When vacuum lines become "old" you can twist them in your hands and they'll being to break apart. You could also bend/kink them and they'll show cracks and signs of dryness. This means it's time to replace them. Remember that a lot of small leaks will have the same effect as a large leak.

The cigar trick actually works since a cigar has a very thick smoke. Also a fireextinguisher would work, but could get rather messy if you mess it up. You could also check differnet areas with a vacuum pump and pinch off areas to test sections at a time. But this could also get a bit trcky if you're not familiar with the system and don't know what you should be pinching off at what times. Either way any of the "quick" methods stated are all very "hackish" and nothing to be considered as "good practice"..

The vacuum leak is one of those issues that no mechanic loves to diagnose. It's usually either diagnoses in 10 seconds or it turns into quite the migraine. I'm sure that most mechanics would have to agree with me that in order to properlly diagnose an issue like this it must be done correctly and without any short cuts.

I've always attacked issues like these with a smoke tester. I have 3 of them personally. Even if the leak is obvious I will still smoke the vacuum system before and after the repair to ensure that there are no other obvious leaks. This will ensure that the vehicles doesn't come back with the same issue & the same cause. If the vehicle was to return without any leaks then it's time to look at one way check valves and switch-over valves that would cause internal leaks in the system. But, that's a whole other story.

So, check the hoses thoroughly, and if everything checks out. Then it's time to bring it to a reputable shop.

Hope this helps.

share|improve this answer

I agree with Gary's assessment about the Manifold gaskets. The Olds 3800 is a "workhorse" engine as is the 3.3, only you don't see much of the 3.3's on the shelf or in the shop. As this is an older piece of iron it stands to reason that the gaskets may need replacing. If you have a tuned ear you can hear a leak or at least hear the approximate location of one and yes you can use the smoke it out method but in the end i know most shops will use the carb o medic solution for a diagnosis, if not to make a quick and accurate diagnosis and save them time and YOU money! As Cinelli pointed out doing a hose by hose check is time consuming and you run the risk of damaging the already brittle plastic vacuum hoses those models use, it's also hard to tell where the smoke is going when the engine is running and or the fan cuts in while doing so. If you were to spray on a cold engine and only in short bursts around gasket surfaces, ie throttle body to intake, intake to engine, the brake booster line and connections, and the hose ends all the while listening for the engine revs to alter in pitch, I think you will in short order find any suspected leak or rule it out as a problem allowing you to move onto other causes. A $5 can of Carb cleaner is cheaper than a $80-$150 an hr., bill. Hope this helped and good luck.

share|improve this answer

if you have an idle and stalling problem with a 3800 series 2, don't mess around with it. change the upper and lower intake manifold gaskets, and the upper plastic intake manifold plenum itself. and cross it off your list. that problem will drive you f-ing nuts. they can leak internally and defy all diagnostics. the lower intake manifold can leak vacuum by pulling from the lifter valley area, under the manifold, from the engine internally. IMPOSSIBLE to find with smoke, spray, etc. just change it. the gaskets are usually mush.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.