my 1987 l98 lost a manifold gasket last september. replaced gasket
and installed a new edelbrock manifold. i have it back togerther but can't get it to start.hasn't run for 7 months. same fuel in tank when
i parked it.good fuel pressure on the rail,good spark. i did manage to get it to start a few times but would only run at about 2500 rpm,no
idle.what did i miss ?

 

Did the gasket seat properly? Maybe there are some leaks?

 

Triple check all your vacuum and sensors

 

diid you take out the distributor and not put it back in same place?

 

This is where most folks make a mistake.

 

I just changed my 86L over to an edelbrock intake. Took a looong time. The edel runners didn't fit right and one broke a flange. Got SLPs. They went on like a dream, except that #2 and #7 injector plugs wouldn't go in. Had to remove the spring clips and amputate the guides for them on the tight inner side. Then they went on, barely. #7 works ok but ticks loudly. (Interestingly, with a stethoscope, the body sounds just like the others, but ticking is audible only in the cap of #7. It does seem to be working ok.)

Had a real issue with Bosch3 injectors (leaked everywhere) so I reused my old Bosch1 stockers.

If you haven't done so and it will run long enough, check your static timing first. And of course your plug wire sequence.

Have you run a smoke test for vacuum? I made sure I passed that one after seeing gobs of smoke with the now defunct edelbrock runners. At that time mine behaved a lot like what you describe.

In the absence of things like broken or forgotten wiring etc., I would just get my hands on a baby oil smoker and a small compressor. See if just 1-4psi of pressure gets you smoke somewhere. I have the advantage of a friend with a smoker, but if you can't find one even just clamping a plastic bag over the throttle body inlet and shooting air (NOT 90psi) into one of the vacuum ports might tell you something. The bag should inflate itself and the only air leakage you should hear or detect ought to be there. Be sure to pull all small hoses and cap off the ports for that. You can reconnect them if you get the smoker. The PCV/purge port on the driver side (near the #3 runner) is a good spot to shoot air or smoke. Smoke has the advantage of showing little leaks (like your lower o-rings on the injectors or your hoses). But you'd have to have a big leak to kill the motor.

Are you running EGR? Mine wouldn't fit under the edelbrock plate/runner combo so I deleted it. Don't know if it would have fit under the slp runners. Moot point now, but a leak there would kill the motor.

At the moment the only casualty I have with the edelbrock baseplate is that the fuel rail bolts won't align with the supply/return line bracket, but that's not a biggie.

Did you eliminate that silly heater line intake (3/8 hose) to the rear crossover and go with a normal gasket with open rear coolant ports? I did. Good move, but won't cause your problem. Just added info.

 

turned out it was the intake runners not sealing properly.
edelbrock intake runners were not machined properly.
went back to the stock set-up.

thank you all for your help and suggestions

 

Bummer. Must be a "bad batch". Great testing.

 

I don't understand how your smoke test works. How do you pressurize the intake system 1-3 psi? It seems to me air would just go through any intake valves that are open and out any exhaust valves that are overlapped. You would have to back off the intake valves to make it a closed system.

 

Two things I guess... first, an open intake generally means a closed exhaust. If both are slightly overlapped open on a cylinder I guess you could bump the starter, or perhaps you just throw lots of air at it. The pressure gauge is on the smoke line itself and it has a valve, so with 90psi on tap I guess you could just overwhelm any leaks. I had no problem reaching 4psi and I know I had several huge leaks on my runners. The smoke still found time to inflate the bag I had clamped over my throttle body and leak through that. It's a good sanity test, and however it works, it does work well.

BTW these things are expensive --- like over $1k. It can't be that hard to make one, can it?