dbcisco

Well I followed suggestions in other threads and so far....
I have a 1992 Z28 305 TPI that won't rev past 3000 RPM in park.
I replaced the fuel filter, the pressure and timing seems to be OK.
I was told to clean the MAF sensor, so I tried to find it (thanks Haines) and ended up taking the throttle body off only to discover there is no MAF! Now I have the throttle body in my hand and all I have is a throttle position sensor that I don't know how to check and filthy coolant soleniod poppet valve that I don't know what it does or is supposed to or how to test it.

So, I have two questions.
How do I test the parts I dissasembled?
If they are OK what else can I check that would cause the low revs at WOT?

Thanks in advance.

faded93bird

Well 1st off your 92 has a speed density computer setup. It uses just an 02, map(which may be your problem) coolent temp, tps, and an iat snesor.

Dose you car throw a code? I'm thinking a $40 map sensor may be your culpret.

dbcisco

No codes. What do the MAP and IAT sensors look like and where are they. Is the MAP at the firewall end of the plenum near the distributor?

Marc 85Z28

ONLY in park? Or does it happen while driving as well? Usually an RPM "wall" like you describe is caused from a restricted catalytic converter.

dbcisco

It won't rev while driving either. Going to disconnect the converter and see what happens. Had the throttle body off and checked everything. All OK there. Just got it back together this evening.

dbcisco

Can't get the cat to slip off the pipe in front. Any tricks to getting it off without mangling it? Clamp really crushed down into it. Any tricks to the little heat pipe too?

DarkshoT

When you checked the pressure did you watch the gauge when you tried to rev it and duplicate the problem?

dbcisco

Fuel pressure pegs the needle (25+) on my guage even at WOT. Guessing the fuel pump is OK.
Timing and vacuum advance are good.
Guess I'll have to use the air chisel to remove the converter.

Marc 85Z28

If you can't get the converter off, you could try to remove the air injection check valves from the manifolds. If the condition improves, a restricted converter is probably the issue.

dbcisco

Thanks for the tip. While trying to get the cat off I re-checked some things.
I put the timing light pickup on each plug wire and got nice pulsing, no missing. I listened to each injector with a screwdriver, nice rythmic clicking on all.

Marc 85Z28

Can you describe the "coolant poppet valve" a little better? Where is it located?

dbcisco

Its the IAC valve. Sorry. Cleaned it and back together. No change.

dbcisco

Dang, body panels that crumple when you lean on them but mufflers that are indestructible. WTH? wore out a muffler chisel and got two inches cut.
What is this? titanium?
Seems like the converter is the problem, I can hear chunks banging around in it.

Marc 85Z28

Pick up an exhaust pipe cutter. It looks like a chain strap, but with lots of little cutting wheels on it. Should cut cleanly through any type of exhaust pipe in under a minute.

dbcisco

Got the pipe loose, still not off, getting a muffler cutter tomorrow. However! with the pipe very loose and some of the chunks falling out of the cat, a quick WOT and right up to redline!