DURTYBIRD

Hey guys!

I did try to browse through the last months posts and didn't see a topic similar to what I have.

I hope you can help me out here. I have a problem that my car will not rev past about 2200-2500 RPM.

A mechanic friend of mine and I have checked the spark that comes thru the wires with a snap-on tool - it's reading very low "kb's" according to him.

Thinking it ignition related and was possibly related to the distributor, I swapped it out... no change. Cap/rotor are new. Thinking it was plugs, we swapped them out - no change. Thinking it was the coil I swapped that out - no change.

With a scan tool connected, the O2 sensor is a bit 'lazy' but it is doing it's job. At idle, the car runs fine and bounces between rich/lean. TPS volts look good. Brand new map sensor since I broke mine reassembling the intake.

It starts fine (actually VERY easy) Only when I bring the RPM up it wil go rich and around 2200 is bogs down. Car does die, just won't ramp up any faster RPM. It's blowing grey smoke (not black and not white).

The car has new accel 8mm wires. I used to have a LT4 hot cam and TFS 23* heads but the car never ran quite right...so I've put it back stock save for an ait pump delete and hedman hedders. The EGR is in place, but disconnected. I checked this to make sure it was sealing properly - it was.

Two things I have yet to check are the vacuum and the compression ratio. Car has over 100k on stock engine. My friend indicated that low CR can cause low KB's on the wires since there is more resistance in the plug 'arc' in the cylinder (presumably from a poor air/fuel compression = less volitile mixture). I could also have a vacuum leak somewhere - but why would it kick in only at higher RPM?

Of course, I suppose the new plug wires could be crappy too...

Any other suggestions? I feel like I just keep throwing money at the problem... I'd like some pointers - maybe someone on here has had the problem before.


Thanks in advance...

Richard

Vader

I'd go back to stock Packard Electric or Sorenson suppression wires. It's the only thing left of the ignition system that you didn't exchange, excecpt the EST portion of the ECM.

You should also test fuel pressure, fuel flow rate, idle vacuum, and a compression or leakage test wouldn't hurt to verify mechanical condition.

Incidentally, I think your mechanic probably meant "KV" - kilovolts.

DURTYBIRD

OK. I'll give that a try.

Quote:

You should also test fuel pressure,

Sorry, I forgot to add that I checked this last night. Initial pressure is right about 40psi (stock regulator)... stays about the same at idle and bumps up to about 50psi when it starts to bog down.

Quote:

fuel flow rate, idle vacuum, and a compression or leakage test wouldn't hurt to verify mechanical condition.

Incidentally, I think your mechanic probably meant "KV" - kilovolts.

Oh, KV... OK, I'll remember that thanks.

DURTYBIRD

on CamaroZ28.com (can I mention that here? ) I posted the same topic and got several responses suggested a clogged catalytic converter.

I asked my mechanic and he indicated that with a clogged converter, the car would run and rev, but would have no power at high revs...

does this sound right?

RB83L69

I've had a stopped-up cat before; even with no load, it wouldn't go past 2500 RPM.

I'd bet that's your problem.

DURTYBIRD

Welp, I have an update.

I picked up a vaccuum guage and hooked it up to the tube for the power brakes. Ran the car and once warm it pulled about 14-15 inches...fairly steady.

Then I ran the RPM up a bit and as it went up, the needle went down. Once I hit the spot where the RPM will not go up anymore, the needle had hit almost zero. The book that came with the guage indicated that if this happens, the likely culprit is a partially blocked muffler or cat converter.

I smiled thinking this confirmed what folks on here thought. Yay!

I put the car up on ramps and dropped the Y-pipe off the headers (the dual cats and the Y pipe are all connected solidly). it only gave me about 1/2" from the bottom of the hedders to the Y-pipe flange. I ran it (briefly because it was 10pm) and it did the SAME THING!!!

I also bought a compression tester, but didn't have time to mess w/it any more.

Any more ideas? This one's a REAL headscratcher for me...

97-1LE

Sounds like a clogged converter. Had that same problem with my 86 a few years ago.

DURTYBIRD

LOL! Someone didn't read the whole thread... HAHAHA!

Air_Adam

Wound't be just a really bad vacuum leak somewere? Or maybe something in your intake system is plugged and not getting enough air to the engine?

DURTYBIRD

Possible, but it DOES hold 14-15 at idle...and the drop seems to be in proportion to the amount the throttle blades are open. My mechanic friend is thinking its possible the cam was installed off a couple degrees... I have a few more things to check, but looks like I will be pulling the front cover yet again...

Quote:

Or maybe something in your intake system is plugged and not getting enough air to the engine?

Nope. Happens even with the intake removed (no MAF since I have a SD system).

Vader

Red,

A restriction in the intake would tend to cause an increase in vacuum with an increase in RPM.

You're running open headers, and still have no power, and vacuum falling off at higher RPM. That sounds like an ignition or valve problem.

Some things that could contribute to your problem are:

• The lifters are pumping up and holding the valves open;
• The valve timing is wrong;
• The ignition is too weak to initiate combustion at the higher pressure from higher RPM (but you would probably notice misfire or afterfire);
• Ignition timing is not advancing correctly with increased engine RPM (back to the comment about the EST);
• Your EGR is not sealing well or has a weakened spring and is opening under increased exhaust pressure;
• Weak/broken valve springs are allowing valve float;
• Push rod interference is holding the valves open;
• OR, you have a Mitsubishi.

Your idle vacuum actually seems a bit low. What is the normal idle RPM that produces this vacuum reading?

Also, unless you have a three-way timing set, you can't change the valve timing by any less than 17.75°. (One tooth of a conventional cam sprocket is almost 18° in timing change.) The aftermarket 3-way timing sets often allow timing changes of 4° one way or the other, so that's the only way you can alter the timing unless you reposition the dowel.

I've had a cam installed one tooth late that exhibited similar symptoms, but check all the other possibilites before digging into the timing cover.

RB83L69

So what happens to the fuel pressure while this is going on?

DURTYBIRD

This is exactly what I have. I have found the problem over the weekend...

The three-way timing set DOES have provisions for 4* advance/retard and straight up. It is adjusted in the install of the crank sprocket. This was installed correctly.

The problem is in the indicators (and the fact this is only the 3rd time I've installed a cam). They are a triangle, a square and a circle (just so happens to be adjacent to the cam timing 'circle'.. Guess what? Yep, I had simply used the wrong one! This resulted in the cam being quite a bit advanced...thus the intake/exhaust valves were open when they weren't supposed to be. I am SO fortunate to have done this with a stock cam, as one with more lift would have smacked the valves into the pistons.

So anyway, thanks to everyone here that has helped out... Even though this was a problem, I have learned A LOT in solving it.

DURTYBIRD

Just to answer - no change from stock...