I just fired up my freshly rebuilt L98 engine in my '89 IROC-Z for the first time tonight... It pretty much started right up after some minor timing adjustments. Everything looked good too--nothing shooting out of the tailpipes, it idled smooth (although high at ~1500 RPM), didn't make any extremely odd noises or anything, and the oil pressure and temperature looked good.

We had it running on the first time for mabye less than five minutes when we noticed some white/gray smoke comming up from around the back of the engine, towards the firewall. Though it wasn't really obvious to me from where it was comming, it seemed to be originating from the passenger's side (could have just been me, though). We shut it off after we tried to look for where exactly it was comming for about 30 seconds. Looked all over the place, found nothing, and then we started it up again to get it hot, and then the smoke started comming up again. It smells like burning plastic or rubber, but we still can't tell for sure where it is comming from.

We've made sure that nothing is touching the exhaust manifolds, although some of the plug wires are close (some touch the aluminum heat shelding around the manifolds, but I'd imagine that those wires are made to handle a lot of heat).

There are only two things that I can think that it might be:

1. About the only thing that I was not completely satisfied with this rebuild was the routing of the wiring harness--specifically, big one that comes from the passenger's side and then across the top of the transmission. A big part of that harness drops down behind the passenger's side head, and it's between everything that has to be around that area, it's pretty much squashed between the head and the firewall. I didn't think that a head would get that hot in such a short amount of time, and I can't think of where else to put the wires to give them more space.

- or -

2. We painted the larger parts of the engine: engine block, the heads, valve covers, and intake manifold. I can remember that some of what we used was called "plasticoat" or something. We made sure that it was paint that was said to withstand high temperatures, though. I don't know if it's the paint curing or not, but again, I wouldn't think that the heads would get that hot that quick (at least not the outside surfaces), and I seriously doubt if the block or intake parts (or valve covers) were hot enough in that time either.

Those are the only two possiblities that I can think of at this point, although I still am not confident that either one is actually the problem. Since this was our first rebuild, my Dad and I were extra-careful to try to avoid silly mistakes (I think we started this rebuild in March or April). I suppose something could have slipped through, though.

Does anyone have any tips or something else that I might want to check? I'm sort of running out of ideas... and I don't want to just let it smoke until it stops (unless I know for sure that there's a reason for it), for fear that a wire or something is melting.

Any help is greatly appreciated. Thanks!

 

Sounds like its all that paint "burning in". As far as the wire bundle going behind the engine, I know on my car the wire bundle actually goes down to the transmission to sit. There is a clip on the bundle that is retained by one of the trans to engine bolts on the driver side.
Did you spill anything on the cat or exhaust? Even if it was when you took the engine apart the residue of the spill could smoke for quite a while.

 

My guess is it will stop burning after twenty minutes or so. Every time I touch my headers it smokes like that for a while, you've got oil on your hands and I guarantee you got it all over your exhaust. If it doesn't smell like oil, coolant, or plastic, you're probably safe. Just watch your oil and coolant levels for the next month.

 

Ill bet the ground strap on the back of the motor is getting red hot and smoking...clean the surface it mounts to of all paint.....

 

I haven't seen a fresh motor start up and not smoke or stink! Everything in there is NEW, just like if you bought a toaster or ceramic heater and plug it in for the first time-they stink and smoke till they get all the NEW crud burnt off.

 

If you didn't use a paint rated for at least 1500* and you put it on the manifolds, I bet that's where it's coming from. I know we just did a cam swap on my motor and cleaned some things up. Well, my brother decided to spray some 500* paint on the headers, I was like that's just goin to burn right off. Started the motor up and it was smokin like crazy.

 

Okay, it looks like most of you agree that it's the paint... I hope that's all it is, too.

But before I go running the engine again and waiting for the smoke to stop, I just want to make sure of one other thing. That wiring harness that comes from the ECM on the passenger's side... I just want to make sure that it's okay for it to be between the head and the firewall like it is right now. We had a lot of trouble with that because we sort of ignored it when we dropped the engine back in, and it wasn't until the engine was bolted in that we realized that we didn't have the harness where we wanted it.

I can leave it where it is if I know that it will be safe, but what I want to make sure of is if that head can, in fact, get hot enough to melt that harness. If it does, then I will definately need to move it, as melting through that harness will definately leave me *screwed*.

Other than that, thanks for the replies... I will also check that ground wire.

BTW -- I just thought of something else that I need to check out... When we first dropped the distributor in, we put some gasket sealant on both sides of the gasket. Well, we've had to take the distributor out twice since then, and it didn't come of "clean" because of the sealant... I wonder if oil is comming out of there and burning on the intake manifold...

 

I agree, it's either paint, or just greasy handprints and dirt and stuff on the manifolds. Pretty normal behavior.

The harness will be OK where you describe. That part of the head doesn't get very hot, only up to coolant temp.

 

I've had a few cars that I swapped motors in and had the harness fall between the head and the firewall (one of those little things you kinda forget about when your droppin in new POWER!! Like the previous post said there's no way it gets hot enough to melt your wiring.