1997 Altima – exhaust problems, lots of them

I’ve been doing a lot of googling the past few hours, and I just came across this thread:
http://www.nissanclub.com/forums/general-nissan-altima-discussion-1993-2001/323852-1998-altima-intake-manifold-gasket-replacement.html

The OP there says:

My problem area is the EGR passages. the two outers are open but the two inner ones are not. I noticed what appears to be pipe plugs threaded into the underside of the intake manifold at about the same area opisite the EGR passages. can I just remove these plugs to access the back side of the EGR passages?

I know the 1998 Altima engine is very similar to my 1997 (my roommate had one 3 years ago and we, well I, worked on it a bit), so the plugs should be in the same spot, yes? If I can locate them, perhaps I don’t need to get the manifold off after all? This is some journey…

[quote=”Timothy S” post=164471]The Altima intake manifold is very difficult to remove, though Eric makes it look manageable in a video on replacing the intake gasket.

If you got the egr pipe and valve off, you have your problem in hand. The valve gets clogged up and starts to leak or get stuck.
You cant gain easy access to the inside of the manifold, but truck/pathfinder/240sx owners can because they dont have the same clearance issues with the firewall and could easily access these plugs. As an Altima owner, if you want the manifold off, you need to remove it while still attached to the head. Plan on a head gasket, because there’s not enough clearance between the fire wall and the engine to get it past the intake manifold studs.
Given this level of difficulty, I’d try cleaning up the valve and egr pipe and testing the back pressure transducer (keeps the egr from opening when it’s not supposed to and looks a lot like the inverted saucer egr valve) as well as the egr solenoid mounted on the passenger end of the hard vacuum lines that run ontop of the intake manifold.[/quote]

I don’t know how I never watched that video before, as I watched the precursor video to that one where he diagnosed the problem (which really helped me narrow it down to the EGR).

Unfortunately, the Altima doesn’t have an EGR pipe. If there’s anything like the pipe the Maxima has, it’s actually built into the structure of the intake manifold. After reading about the plug bolts, I went out and looked again (even though it’s late). I may have identified them? These are exactly in line with each other, and there may be a tube running between them. It’s also about the same level as what I think is the very bottom of the chamber that leads to the EGR valve itself. So I think the EGR air goes up into the valve, then down into this tube that distributes it to all 4 cylinder intakes. I’ve temporarily lifted the fuel rail with the injectors out of the way here for clarity.

I think I can get to these plugs, but I don’t currently have the hardware to undo them. Shouldn’t cost too much for something that fits, right? Then, if this is a big pipe for the EGR, I’ll need to get some loooooong brushes. To recap, I’ve actually already replaced the EGR valve itself as well as what I think you’re calling the transducer (it’s a disc- or saucer-looking thing that connects to the EGR valve, and is not the solenoid).

[quote=”Timothy S” post=164475]You have removed the egr pipe with the valve. It connects to the exhaust manifold and loops around the engine under the distributor. The cast in passage for the egr appears to exactly where you indicated on your picture of the intake manifold. If I remember from my ’98 Altima the plugs have a hex head, but I never needed to remove them. Maybe try a large hex bit for a 3/8 drive ratchet and pray the corroded aluminum plugs don’t strip or round off.[/quote]

I actually had to go outside again and check, as I didn’t remember my car having the pipe that Eric talks about and shows around 5:35 in that video. Sure enough, there it is and I can see that it’s connected to the manifold with a pair of 10mm bolts. I’ll take that off tomorrow. It’s not really anywhere near the EGR valve itself, at least not obviously so. Without that video showing me where it was, I never would have found it. Unfortunately, the big nut that attaches to the EGR pipe itself looks extremely rusted. I would not be surprised if I couldn’t get it off at all… but hopefully I can make progress by first detaching it from the manifold.

Thanks a ton for your helpful input.

The pipe itself being clogged would explain why the EGR vacuum line being disconnected was only a temporary fix (for about 2 weeks), and why taking some of the screws out that hold the exhaust manifold heat shield on and also open up holes in the manifold itself (there is one on each side) seemed to improve the running, as that would let off some of the pressure ahead of the EGR pipe itself.

I have a torch, so maybe I can get the 24mm nut off of the exhaust manifold itself. We’ll see. The engine has run hot in the past on several occasion so it might be pretty well baked on there.

I have a basic vacuum gauge but not really sure how to use it in this case.

I have the reverse problem, sort of – the worst of the problem is at idle. Under load, it runs fine (if really inefficiently).

I’m also not sure if I can loosen the bolts that go to the cat. Maybe. I’ve looked in that area before because I was thinking that if I took it off, and it ran fine, I’d have identified the cat as the problem. Unfortunately, my cat is welded on (I think it has been replaced once before) and the warm-up cat just after the exhaust manifold and O2 sensor is impossible for me to get off without lifting the car far enough off the ground that I can get sufficient torque on the rusty bolts attached from underneath. Something I could do in my backyard, but I’d have to build a couple of ramps. Not something I’m eager to do.

OK, I got to the EGR pipe itself. Eric’s video told me I needed a 30mm and 24mm wrench, so I got some more wrenches. The 30mm nut at the top of the pipe came right off – I think it must have been taken off in December 2014 when I had the intake manifold gasket repaired. Looked like there was some silicon on the threads. So that’s cool.

However, I took the exhaust manifold heat shield off (also requires taking out the radiator fans), and got to the 24mm nut at the bottom. It’s completely rust-frozen in, it seems. Here’s a pic before I used a brass wire brush and slow-sprayed some penetrating oil. As you can see, I started to round the 24mm nut off a little bit when I applied my rubber mallet to the wrench, so I stopped.

While getting the radiator fans out, I spilled some coolant. I’ll need to clean that up (I inherited a really messy engine compartment and have never bothered to clean it up… :blush: ).

Any advice? I have some 12-inch stainless steel tube cleaning brushes on the way, and I can get into the top end of the pipe, but I’ve read that the bottom end is the one more likely to be clogged and it’s not exactly a straight pipe. If I can’t get the nut off, could I hacksaw the pipe, clean it out from the break, and then solder on a “patch”, which I saw somebody else do?

You can also see into the warm-up three-way cat here. When I peer in through that O2 hole, it appears to be all white – so it’s fine, right?

[quote=”Timothy S” post=164784]Can you unbolt the catalytic convertor from the exhaust manifold, just below the egr pipe connection? That might allow you to access the pipe. On the Altima I had in Texas, that was all one piece, with a support bracket bolted to the block at the bottom of the manifold/ downpipe assembly. Looks like you can go after 6 bolts connecting the pre cat to the exhaust manifold and possibly a support bolt and drop the pre cat out the bottom of the engine bay. It’s also got 3 nuts connecting it to a flexible exhaust line under the engine.[/quote]

Thanks for keeping up with the thread, I really appreciate it. It’s nice to have a second voice.

I can get to those bolts holding the pre-cat on, maybe. They are done from underneath, but now that I’m working in a driveway and not at the curb I can jack up the car and maybe get at them from underneath. I will try it sometime this week. I already know I can get the exhaust manifold off of the engine block, as I’ve taken those fasteners off before when I thought I could get the pre-cat out. I may need to take some more stuff out of the engine compartment if I go that route, as I may not be able to pull the pre-cat + EGR pipe assembly out given the shape of the pipe itself. Here’s a pic from before I took the heat shield off. I may have to take the distributor assembly out if I want to take the manifold + EGR pipe out.

If I 100% knew this was the problem, I would just replace the exhaust manifold (~$80) and EGR pipe (~$40) themselves. In this pic you can see that my exhaust manifold may have a crack all the way through it, right in the middle. :dry: You can also see the after effects of a cracked radiator from ~2012 on some of the things below the manifold (you can see that coolant looked into the engine bay). I’ll have to clean that up, too.