No engine power after warmup

hesitation

#1

1996 Camaro RS, 170k miles, 3.8 liter, 5spd. Car has been fully functional. 10k miles ago, I changed fuel pump, filter plugs and wires with high quality parts. Recently got EGR code and also started to act up when driving. Took it to my trusted, long time, certified mechanic. He saw code and changed EGR. Ran good for short, cold, test drive and no codes. When I got it and drove away, it went back to bad. No power with throttling, but great idle. Puts out the classical “bog” sounds and stutters/sputters/surges. I can only get about 35 mph out of my White Mullet once it’s warm. All sensors and pressures checked good on live data viewer. I then changed coils and ignition controller. Didn’t fix it. I blanked off EGR ports, didn’t fix it. The car cooled off and I restarted. It ran fine for a few minutes, until I suspect it went from open loop to closed loop fuel/air control. I now guess it’s the O2’s or MAP, but they didn’t code out, and presumably gave a reading at the shop. Could the O2’s be way off base once the engine warms up and drive the fuel ratio way lean? I plan on ordering new O2’s, but would like some opinions in the meantime.


#2

Get a new cat. What brand is fuel pump


#3

Here’s an idea . . .

Check for pending fault codes

Even though everything checks out, there may be some things which haven’t yet failed often enough to set that code

Might want to check out some mode 6 data. Perhaps something is on the verge of failing

What about the TPS? Does it check out?


#4

Have you checked the actual fuel pressure? This is just as important as pulse width to get the right fuel mix in the car. There are no codes for fuel delivery, since there are no sensors on the fuel line before the injectors. Low fuel pressure will kill power.


#5

Your thinking is exactly what I would have suggested. It sounds like it’s failing when the O2 loop kicks in. I’d change the O2 without hesitation.


#6

New AC Delco fuel pump/filter 10k miles ago (last year). [I got this car for $1k because only fuel pump needed changed. I replaced it, and more, the hard/right way] Fuel gage on fuel rail checked out great at mechanic shop, even while engine was falling on its face. Opened the gage line and fuel came out like crazy in no time; gas quantity and quality perfect. All sensor signals appeared fine. Had a suggestion from JJStang to disconnect O2’s to make it run in open loop full time. JJStang things O2’s may be very slow to respond and will completely die soon enough. I’ll try tonight maybe if I can find an O2 socket. New O2’s on order from Rock Auto. The only open item is if that fails to displace the symptoms, the ECU is the only other link I can guess. Auto Zone has reman’s for $130 with a fresh flash. That’s cheaper than the ignition controller!


#7

Have you checked if the MAP sensor is working properly once the engine gets hot?

Tester


#8

A restricted exhaust system (catalytic converter) can trigger EGR performance faults and loss of power. Does the catalytic converter rattle when you hit it?

Observe a vacuum gauge while running in neutral, the vacuum should increase to 22-25" @ 3000 RPM. If the vacuum reading decreases with engine speed you have an exhaust restriction.


#9

Your car has a fuel pressure test port specifically to check actual fuel pressure. Also, as mentioned above, a vacuum gauge can tell you a lot about how the engine is operating. Autozone has both gauges in their rent-a-tool selection, and diagnosis is much cheaper than throwing parts at it.


#10

Changed O2’s & MAP to no avail. Had battery disconnected all week to drop old memory. Sprayed starter fluid all over intake and no rpm change. No rattling from cat after rubber mallet test. Found the vacuum line boot very cracked. Replaced it, no improvement. Checked inlet air control valve. It was crud filled and uneven wear marks on cone. I cleaned it with CRC. I had it out when tried to start to see if it would move. Didn’t seem obvious that it moved. Then another time it shot out and plastic crumbs with it. That could have been the CRC dissolving the plastic, don’t know, spray can says warnings about rubber. New IAC tomorrow at Auto Zone. I think I will decouple the cat too. Still no codes after many times holding high rpm’s while falling on it’s face. Does this car have a PCV valve?

Thanks everyone for all the help. Anyone know a good kit to put in a modern 5.3 v8 into this car, with the 5 speed? I pretty much only want stock performance, with maybe some minor increases. I want a dependable daily hot rod. I think the 6.0 v8 is too pricey and to much power for the original drive line. 325 hp should be ok for 5sp, driveshaft, and axel.


#11

It has a pcv in the valve cover with a attached vacuum line.


#12

I FOUND THE PROBLEM!!! Something had caused the cat to shed its coating. Darn shedding cats! When I tapped on it the first time with a rubber mallet, it was the wrong angle to make it move. Once I put it back up in the air, I tapped vertically from below with a rhythmic beat to get a standing wave in the whole pipe. There was a little rattle, as if it were two pieces, no more. That was enough to give it the college try and cut it out. Once it was out, it heard more apparent pieces rattling. Then I shook it over the trash, and out came the glitter sized flakes like a salt shaker. I suppose after running for a bit, the flakes would fly around and fill the gas passes. That’s why I thought it was an open loop verses closed loop problem. I fired up White Mullet and all was well in the universe once again. I reckon I ran lean or had some misfiring due to sporadic engine codes. I guess this killed the cat, meow. I put in a cheater pipe to test it out. That was the problem! After all, who attacks the cat first, or how do you test a choked cat? Now it sounds like a cheap hot rod; not very pleasant. It seems to have gained a little power since my day one. However, I can tell the cam has in/out valve overlap that has been factory engineered for the OE backpressure. Now it has the slight popping and backfire under deceleration, just like a cheap hot rod. Nothing like getting everyone’s attention when your car runs a 16.5 second quarter mile. That’s Prius territory. I will put a cat back on. A universal from Auto Zone is about $60 and Rock Auto $45, or so. Thanks for all y’all’s help. May this help someone else in their time of desperation. I did find in the Haynes manual a write up about measuring backpressures from the O2 bungs to be no more than 5 psi. Who knew?! Not me!! Farewell and God bless. White Mullet, out.


#13

Post script; it’s just like the banana in the tail pipe from ‘Beverly Hills Cop’.


#14

Cavell told you to get a new cat and Nevada-545 told you how to test it. It amazes me how much money people will spend to throw parts at a problem but won’t buy something as cheap as a vacuum gauge to diagnose an exhaust restriction or sticking valves.

Not everything sets a code or at least not in the system that is the problem.


#15

If the plug wires you replaced were the originals then it’s possible this problem could have been caused by those wires. At one time GM had a Campaign (basically a voluntary recall limited in scope) for plug wires on these cars.

My oldest son has owned a '96 RS with the 3.8 for about 16 years now and he got a set of free wires out of it about a dozen years ago. Right about a quarter million miles now and still fires right up every time followed by getting about 30 MPG on the road.

We’ve actually got a V-8 engine built for that car when and if the V-6 goes south. It’s a Cadillac 500 with an aluminum intake, mild cam, and 425 heads which bumps the compression ratio up a point or two.