I have an 85 and in Penna I can get an antique registration which means no inspections or emissions test. I've got he heads off and replaced with aluminum from an 86. I've already stripped off the AIR pump, gasket matched everything, changed the cam and added 1.6 roller rockers and was thinking of eliminating the cat and EGR. With an 85 is there any value to eliminating the Cat and EGR or will this create problems with the ECM?

Eliminating the cat will make things stink. Eliminating the EGR is pointless. The EGR helps reduce detonation, so leave it.

If you want to upgrade the exhaust, don't just remove the cat. It will resonate like a bitch!

Read the thread by herman8r. I gave him some good exhaust suggestions there.

Bogus, is there a way to test the EGR? Also can you clean it?

I would want to keep the EGR, but it might be a hassle to. The 85 EGR valve won't work with '86 heads, they use an external passage.

You'd need an 86 intake base (or edelbrock) and you'd need to run an external tube to the header.

The egr valve can be tested by pulling a vaccum on it and seeing if the diaphram stays up. To test the system though there's a solenoid that is grounded by the ECM (or activated when put in diagnostic mode) that routes engine vacuum to the EGR valve. There's also a temp sensor, but I think it's only function is to see if the EGR valve is open or shut. The vacuum in the EGR should bleed off from exhaust backpressure. If you have a very unrestricted exhaust (such as no cat or mufflers), it can cause the EGR to stay open, which can throw a code.

I have no need for a cat beyond biannual inspections, but it does quiet the exhaust down nicely. I have no mufflers, and with no cat I think it'd be overkill. I welded a 3" carsound in there, $50. Other than the potential for lack of backpressure throwing an egr code, cat or no cat will not effect the ECM.

Seems like the easier way to go would be to program out the EGR (dunno how). I'm not sure what changes to the chip would be wanted to compensate for not having an EGR, as it helps keep cylinder temps down which might otherwise cause preignition. Obviously this is less of a concern with aluminum heads though.

EGR only works on cruise, but useful for a daily driver that uses cheap gas.

AIR pump eliminated could cause a lean condition. When AIR injection is set to MANIFOLD (three modes present, cat, manifold, and divert which happens at WOT) it subtracts .100 from the 02 feedback when calculating fuel correction because normally fresh air is injected into the exhaust stream.

This in combination of a lack of EGR I guess could lead to pre ignition. Although, like he said, the aluminum heads should help a little. Then again, your increasing compression ratio by going from 64cc to 58cc.


The '85 ECM is a turd, and any EFI car needs tuning after making modifications so keep that in mind.

I wouldn't get to caught up on the 'stinky exhaust' nonsense. My neighbors '67 Firebird doesn't stink any more than my 2000 Dodge RAM (which has 3 cats vs his none).

-- Joe

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I disagree with this. I believe the a.i.r. pump, in '85 at least, only diverts to the manifolds during open loop. Therefore the O2 feedback would never be affected by it.

I don't know about the rotten egg smell, but my truck has no cat and the exhaust stinks, but I think it's more related to the previous owner's shitty rebuild puking oil past the rings.

I have both an 85 and an 86 manifold. Both have a place to mount the EGR in the middle of the manifold. The 85 has the temp sensor incorporated in the EGR mount. The 86 has a separate mount close to the distributor where a tube mounts along with the temp sensor. Is this the external tube to the header you're talking about Centralcoaster? Could this be routed down to the cat? From what I reading I can't run an 86 manifold with the EGR set up like an 85?

The 86 EGR, manifold, heads, and headers are a matched set.

The 85 EGR, manifold, heads, and headers are a matched set.

If you want to mix any of those 85 and 86 parts, you'll need t o use your imagination. The 86 EGR as you said, has a tube connection on it, the other end of this tube goes to a 2-bolt flange on a small pipe that is welded to the #8 header primary tube. The 85 header doesn't have this tube.

This is why I would consider just ditching the EGR entirely.

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I don't have a commented hack in front of me of the '870 code, but I'm fairly certain the AIR logic was the same on all L98s. Could be wrong though. As you know, the 1985 was a one off ECM, used only that year in y and f body, never again. Very strange.

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The idea behind the cat is to combust trace gases, not ounces of liquid fuel. If the car is poorly tuned, the cat will burn out anyway. A lot of guys have passed tailpipe sniffers on the dyno without cats. A good cat will mask a poorly operating engine, but I think if the engine is tuned properly to begin with the cat is probably not needed.


-- Joe

Joe, I checked the 85 FSM to be sure.

Open loop = exhaust ports
Closed loop = converter
Rich A/F, C.E.L., deceleration, high rpm, electrical failure = diverter (muffler to engine bay)

And also fwiw, the 85 EGR system:

EGR usually open during: warm engine operation, above idle speed, in drive gear (Auto)




During cold operation and at idle, ECM grounds solenoid which blocks vacuum to EGR. The ECM controls EGR with a duty cycle based on TPS, CTS, MAF.

There should be no EGR in park or neutral, low TPS, or WOT.

The EGR temp switch closes when it's seeing hot exhaust gas.

Code 32 should trip if the EGR temp switch is closed during startup.

Code 32 should also trip if the temp switch is open (cold) when the computer thinks it should be closed (hot), with the following conditions occuring for 4 minutes: CTS>176F, EGR duty cycle > 27%, TPS above idle but below WOT and code 21,22,33,34 not present.

FWIW I drove around with a bad (open) temp switch for awhile and it never threw a code.

I'm wondering what would happen if the temp switch was left connected? I'm definitely going to use the 86 manifold since I've got it ported and cleaned up. Most likely will make up block off plates.

It might set a code because it won't heat up like it's supposed to without exhaust flowing over it.

But like I said, mine was disconnected and never threw a code. Give it a shot.

If you doing that anyways, you might look into a different intake.

the stock L98 is great for low end torque, but it was designed for 305

Runs out of air & rpm.

I have Pennsylvania classic plates. No emissions test needed. Your car is to be substantially restored to stock in order to get them. You have to send in pictures. Hopefully you have a few pics of the motor while it appeared stock. If not, have someone on here send you a couple. There is also a 5,000 mile exemption, if you drive your car less than that per year you can get an emissions exemption, but I really didn't look into that. I wanted my car to be a sleeper and the classic plate just finishes that off perfectly!

Dan, I went over the form for the application for antique registration and it seems to rely upon the applicant to say if any engine modifications were made as well as any exhaust modifications. If those were made, then you're supposed to include photos of the engine bay. So what is to prevent you from saying there were no modifications and then you just have to submit exterior photos.

That may be the case. The notary told me what pics need included, I never read that part of the application myself. Are you applying for classic or antique plates? Mine are classic. Isn't there a restriction with antique plates that you can't drive after dark or something of that nature?

What is the benefit of antique or classic plates?

When I had my vette, I had 20k insurance policy which was like $500 a year. Reg fees are $30 / year.

-- Joe

Read the fine print carefully.

Many "classic" insurance policies bill you for whatever "stated value" you want, but when it comes time to pay a loss, you get the "actual cash value" which can be wayyyy less and is determined by their cold-hearted computer program.

"Agreed value" is generally the way to go, but it really depends on the carrier, so read the fine print.

http://www.classic-british-cars.com/classic-car-insurance.html

To top it off, most agents around here in SoCal at least (classic car capital of the world?) have no experience with this stuff, and may promise you the world over the phone. But they aren't the ones writing the checks, and trust me the adjusters WILL know the rules.

I went with Hagerty insurance which was easy to do once I had the classic plates. I went with stated value and if my car is crashed I'll get that stated value for it if it is crashed bad enough.

With classic plates your registration fee that you pay when you get the plates is the last you will ever pay, it is a lifetime registration. Also no emissions inspection therefore no anuual emissions inspection fee.

Hagerty's policies are Agreed Value, not Stated Value.

What is the difference between Hagerty's "Agreed Value" coverage and other types of insurance coverage?
A. Agreed Value insurance policies guarantee that you will receive the full insured value of your vehicle in the event of a total loss. There is no depreciation of a vehicle’s value with an “Agreed Value” policy, unlike an “Actual Cash Value” policy, which depreciates the value of a car as it ages, or a “Stated Value” policy, which generally requires an insurer to pay only “up to” the stated amount.