Your MAP sensor is fine - you don't need to keep testing it. The problem is the MAP reading. You have totally inadequate vacuum at idle. That is the key to your problem.

The IAC is not responding to a rich mixture. It only responds to idle speed. It is opening all the way because there is inadequate air available to keep the engine idling at the rpm programmed into the PCM. You proved this when you cracked the TB blades.... as you opened them up, the IAC went down... it was getting the air it needed from another source.

 

Here's the plan for the weekend. Saturday morning, do a compresstion test on all accessible cylinders. At the same time I'll check #1 cylinder with the valve cover off and watch valve actuation.

If it's easy enough to do, I'll drop the cats sat. nite/ Sunday and check for restricted exhaust...My test yesterday theorhetically proved that false, but it may be worth trying to completely eliminate that from the equation.

Does anybody know where I can get a spark KV tester for cheap? I'd like to re-check all spark plug wire outputs....

Any other thoughts?

 

from the sounds of it the vette isn't making the power you claim it is

 

How about..... 1,125HP under ONE hood!

 

Injuneer, shoebox, and everyone else, here's the results of the weekend test.

Cylinder compression test:

#1: 190
#3: 190
#5: 205
#7: 205
#2: 200
#4: 200
#6: 200
#8: 200

It appears that the compression is solid, and I assume the valves are seating properly....

I also put some new plugs in the car and it ran a little better, but not much....

Another thing I noted was when I pulled the old plugs out again, this time they were white instead of being fouled black. Before I pulled them, I was oscillating the throttle to get it to rev to 2500 rpm and holding it there....

Then I pulled the new plugs back out after letting it idle for a little while (to keep from fouling them). And they were black just like the first time.

Does this mean that it's running extremely rich at idle, and lean at high rpm's?????

How could this be????

 

No, not really. Doesn't mean much to me. At idle and part throttle the computer is adjusting to maintain the right amount of fuel. Judging by the datamaster files you sent me the fueling is fine.

You're still not addressing the fact that the car is not maintaining the idle rpm that the computer has set for it.
In one of the datamaster logs you sent me the idle is fine for the first third of the log, then you start screwing with the throttle and the IAC pegs at 160 and then can not achieve it's desired idle anymore.
Before you do anything else I would be playing with the throttle stop screw and getting the IAC counts down so that the computer can adjust to allow enough air into the motor at idle. Right now, it can't. That's why the computer is maxing out the IAC and then the car won't idle. If you still can't get the IAC to stay down after repeated attempts at adjusting it, then you have a bad IAC.
But I think that if you've checked valve adjustment and it's ok, then you have a huge vacuum leak that you haven't found. I think this is your problem. It would also cause your IAC counts to go up as the engine needs more air at idle.

 

but wouldn't a vac leak cause his IAC counts to go down?(i.e., a large vac leak would cause a 0 IAC count)

 

Yes.

That's why he need to address the MAP problem, and the whacked out timing (if he's using the timing light correctly, and marked the damper correctly). The high IAC count is not consistant with a vacuum leak.

Just a thought.... does your MAP sensor have the little rubber seal that goes on the nipple that sticks into the intake manifold?

 

O.K. tonight, I went out and played around with the IAC valve a little bit...I think I posted before that I was able to take a screwdriver and crack the throttle a little bit, just enough to get the IAC counts to go to 0 instead of pegging out at 160. Well I adjusted the throttle setting at idle semi-permanently at idle to carck the throttle plates a little more at idle. They weren't open enough to register as throttle input (<.9V) so the computer diddn't add any fuel. The IAC ramped down to 0 (after I did an IAC reset procedure). The Idle was a little high at that point (900 RPM when 850 was called for) but not too bad. I then tried to rev it up with the IAC closed, and the same thing happened....Stalled out....So I think I can completely rule out the IAC.....
But what's interesting is the "service ASR" light came on. It took me a while to figure out how to pull CCM and ASR/ABS codes...But when I did, I got the following codes:

Module 1: (CCM) H54
Module 9: (ASR) H62, H65, and H72

The H54 is a "fuel enable failure" code
the H62 is a "tach pulses malfunction"
the H65 is a "adjuster assembly malfunction"
the H72 is a "serial data link malfunction"

The H62 is an interesting code...If it's partially shorted to ground then "driveability and poor engine performance may result" this is tied into the "tach filter" from the coil......

Anybody have experience with this stuff? Have I found a smoking gun?????

 

It's been a little while since I've posted...But here's what I've worked on in the meantime...The ASR code H62 diddn't turn up anything, the connection to the tach filter was good..no problems there. But, the H65 is real, I'm getting +12 v on the negative side of the traction control motor that is coming from the ASR computer. I haven't gone any farther, because it looks like the voltage is coming from the computer, and I don't want to buy another computer unless I'm completely sure. In the meantime, I borrowed a spark Kv tester, and all the cylinders ranged from 15Kv to 19 Kv. All looked normal. Finally, I wanted to put the plugged cat idea to bed, so I disconnected the exhaust manifolds from the block and ran the engine for a few seconds....Absolutely no change.....

Now I'm REALLY running out of ideas...This weekend, I'm going to pull the timing chain cover, distributor, valve cover, and intake manifold. I'm going to turn the engine over by hand, and watch valve timing, crankshaft timing, and the "dot-to-dot" alignment of the cam/crank gears to MAKE SURE ONCE & FOR ALL that the engine timing is absolutely correct. I'm also going to check & eliminate the possibility of intake manifold leaks....

Is there anything else I can try before I do this final step???

 

Don't make a big deal out of checking the valve timing. As I explained earlier, simply find TDC exhaust on number one, and rock the engine back and forth, and observe the overlap of the intake and exhaust valves. If the overlap is centered about the TDC position, the timing is correct. Why remove the timing cover and do all that work?

 

A vacuum three way coupling is setting near the PCM between it and the Air conditioner box. it hides behind some cabling. GM makes this thing out of cheap plastic and I have had one to break. Check that. It sounds like you have a major vaccum leak, or possibly and burnt intake valve. You can troubleshoot the intake valve Idea buy removing plugs and loosening the rocker arms all the way up for that cylinder to close on each cylinder, then use compressed air into the sparkplug hole. If you have air blowing out the intake, it is a burnt or bent intake valve. If you hear the air blowing out exhaust , you have a exhaust valve seating problem. I currently have a bent #6 cyclinder exhaust valve in my 95 Z28, and it runs really bad, popping backfiring. I can disconnect the injector connector for cylinder #6 and the engine runs fine, except for losing cylinder#6. Your compression readings were good, i do not know if you have a valve problem, just keeps bugging me about the IAC going to max.

Greg

 

Do you have Hydraulic Roller lifters in your 93. I had to replace my lifters as i failed to adjust the valvelash correctly (slightly too tight). If you get into the valley and can access a lifter, see if the little springloaded Rod cup is not mauled to the point you have a solid roller lifter. These lifters are so easy to screw up with using old school techniques of setting lash. I messed up all my lifters first run by using the set #1 Cylinder to TDC compression, and tightening the rockers until i could not rotate the push rod technique. New way is test how much stroke the spring travel has then tighten the rocker so that the push rod just budges the spring loaded receiver off its seat. Then once the engine is running adjust the rockers at idle. Never make more than an 1/8 rotation of the ratchet at a time to precisely find no lash point, then no more than 1/4 turn after that.

The lifters I removed from my 95 looked fine, and worked, but the cup in the top of the lifter was bowled so deep, to the point the cup was frozen in place. no spring action at all.

 

In your first or second post you said you replaced the timing chain, right? Assuming it was done correctly....which it's more difficult then not, I'd look at that 'tach filter'. Does your tach needle bounce around when the car is running? That filter is nothing but a capacitor with one leg to the tach line and the other to ground. It's derived from the opti optical pickup and feeds the tach and the PCM I beleive. The strange timing,(60degs)
maybe something to look into, but I don't know why that would have changed overnight. Did someone put water in the gas tank and it that why it was cleaned and you replaced the timing chain before cleaning the tank? I guess a time line would be helpful in determining if it was the chicken before the egg or vise versa.
Just my 2cents....tryin' the help out,
Doug

 

I haven't seen this mentioned yet.

I've seen several others with 93's who have been experiencing injector driver failures. The injector drivers are in the computer and funtion to do the actual opening and closing of each injector. The 93s, if I remember correctly, run a batch fire ignition which means that each driver is firing 2 injectors. Those with this problem experienced overly rich conditions and was immediately fixed by replacing the computer.

I have your Datamaster files yet they do not indicate a driver failure, have you tried swapping in a different set of injectors. Definitely sounds as though you are getting too much fuel and the IAC is going wide open to try and give it more air to go with all that fuel.