Hi all,

Just bought a 1992 Camaro RS 305 TBI. It drove home after purchase (it had been sitting for months) and drove it decently with a mild hesitation. After I got it home, I sprayed the throttle body with carb cleaner and it ran well for a day. Then the hesitation has come back with a vengeance and has been haunting me for weeks.

Rebuilt the throttle body, replaced fuel regulator, fuel filter, cap, rotor, and plugs. Someone seems to have been chasing this as wires, O2 sensor, coil, distributor, and map sensor seem recently replaced.

Fuel pressure in line to throttle body is currently a little high (16-20psi).

I replaced the PCV, EGR, and again the MAP and still having issues. It even seems worse now. It used to be fine at idle in Park until I put it Drive and presented the engine load. Now it struggles even at idle. In Drive, if I open the throttle, it bogs down and hesitates to catch up itself.

Attached is a cold start from a reconnected battery (raw text from WinALDL and an HTML version that was formatted with correct spacing). Any help is greatly appreciated. I just want to drive it but it's been in the garage since day 2!

Thanks all,
Paul

 

Have you checked timing? I was dealing with a bog/hesitation and although I set the car to 0 BTDC and 2 BTDC with the timing wire unplugged, as per the guides, the car didnt like throttle. I ended up trying the old school method of just turning the distributor until it sounded right and stabbed the throttle at the linkage until it responded appropriately.

Spark plugs and wires are good? CTS is working properly and reading as it should?

You also mentioned high fuel pressure, possibly the return line is clogged a little bit. I dealt with that as well.

TPS voltage is good?

Sometimes the ICM that resides under the distrubtor cap that plugs into the coil is the problem, I am pretty sure there is a way to test it. Just not sure of the process.

 

How did you check the fuel pressure? The results sound like it's deadheaded. It needs to be tee'd into the feed line. I'd start off by getting the injectors cleaned. I have one of these and I get the car good and hot and let it idle on cleaner for a half hour or more. I use BG 44k cleaners.

 

Also make sure the egr valve isn't opening up at idle. Use a vacuum gauge at that connection.

 

You've replaced a bunch of parts without ever diagnosing that they were faulty. Some of that--the tune-up items--would be considered "consumable", so that's no big deal. Other parts aren't consumable, and with the current state of the world, the new parts from China may be worse than the OEM parts you removed.

Moreover, replacing parts does not fix the wire harness connecting sensors to the computer, or fix vacuum hoses/vacuum leaks. You haven't checked cranking compression pressure, or verified the valve action of all sixteen valves. You'd want to assure that when #1 piston is at TDC, the timing mark on the damper is aligned with "zero" on the timing indicator. And if the catalyst is plugged, the engine won't run right no matter what.

Is the gauge accurate? Are you trying to read a spec pressure of 9--13 psi on a gauge that goes all the way to 100 psi or higher?

You've done some of this. Now do the rest.

The Usual Four:

1. Verify System Voltage. Most “12-volt” batteries should show 12.6—12.8 when fully charged, depending on battery construction and temperature. A “12-volt” battery measuring 12 volts on an accurate voltmeter is near-dead. Assure battery connections are clean and tight. Battery voltage during cranking should never go below 9.5 volts, and then only when the battery is very cold (below freezing.) Higher voltage during cranking is better. Running voltage--alternator charging--is generally 14.x volts measured at the alternator output terminal.
2. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. TBI systems don't hold pressure when the pump stops running, but the other fuel injection styles should. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.) Use Top Tier fuel which has additional detergents beyond what the EPA mandates, to keep the injectors clean. Remember, a "weak" fuel pump can be a defective pump...or low voltage to the pump, or a poor fuel pump ground, or a plugging fuel filter including the filter sock on the bottom of the pump.
3. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Use quality parts sourced from an authorized seller (NO COUNTERFEIT PARTS FROM AMAZON, EBAY, OR OTHER SKETCHY SELLERS!) Be sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance. Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”. The catalyst output temperature should be HIGHER than the inlet temperature once the engine is at full operating temperature.
4. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle.

Amazon has spark-testers at reasonable cost. There's multiple vendors, and several designs. You want one where the spark has to jump a calibrated gap suitable for HEI (not ballast-resistor style ignitions.) The kind where the spark lights-up a light bulb are USELESS.

My favorite style:
http://www.amazon.com/dp/B003WZXAWK/...=2VLYZKC3HBBDO



First Guess: You'd be WAY better-off to use an actual scan tool than whatever you're currently using to generate the tables you posted previously.

 

So maybe a little more background is needed. Someone had been chasing this and already replaced a lot of what I replaced with non-genuine parts (including, sadly, the injectors). I've done my best to research every part I replace and always get A/C Delco from local shops or find the most liked alternate on this forum.

The tables are data logs from WinALDL which also shows me live data stream from all sensors as well as codes and ECM flags.

I've verified sensors and function using my physical official 1992 Camaro Service manual.

The TPS, CTS, IAT, MAP, ESC (Knock sensor and circuit) are all fine.

Following the diagnosis flow of the fuel pressure, I tee on the feed line using my OTC Master Fuel Pressure Test kit and get 20 PSI. When I did as the service manual indicated and took off the fuel return line and dumped it into a bucket, the pressure was 16 PSI, possibly indicating a mild obstruction in the return line. Fuel pressure dissipated when fuel pump was not on (it's on for two seconds when car is "ON" and left there before starting).

Interestingly, I decided to replace the plug wires as they were a brand I was unaware of, with A/C Delco ones and for a few minutes the car ran very well, but as it warmed up, the original symptoms returned. With that in mind, it seems to be a spark issue. As others mentioned here and other threads, perhaps the ICM is the culprit. In the same breath something seems to be making the ECM lean out the car as I can add carb cleaner to the throttle body and the idle picks right up for a second. I'll definitely grab the HEI spark tester

I need to verify the IAC as well which is on the list of things to diagnose as well. I even replaced the plugs again (A/C Delco) just incase they were getting damaged from the symptoms.

Thanks all.

 

Can you verify that the engine is a stock LO3? i.e. swapped to 350, aftermarket camshaft, headers, Holley tbi etc.

Based on the data log, couple of observations...

TPS volts start at 1.2v drops to .7 assuming after engine start then at some point resumes 1.2v.
Open loop O2 starts off at ~reference sensor volts then plummets lean, starts to swing rich lean as it enters closed loop
BLM indicates 150 lean for most of the closed loop which ideally should be 128
IAC as the engine warms up plummets to a big fat zero.

Idk how's all your vacuum hoses?