My engine is psycho.
I've recently revamped the 350ci SBC in my '69 Camaro.
My upgrades are:
GM 78cc "D" iron heads => AFR 195 eliminators (64cc), 7mm valvetrain
Weiand stealth dual plane intake => same, port matched to gasket
Holley 1-5/8" headers => dynatech 1-3/4" to 1-7/8" stepped, ceramic coat headers
2 bolt main upgraded to 2 bolt ARP studs
steel crankshaft scrapper
new gear reduction starter
So I did all this upgrading and when I was done, I was having trouble starting the car, it wasn't turning over much at all. I replaced the 1974 starter with a new high torque one, came with torque and rpm spec sheet. powermaster something or other.
Anyways, the car WAS running and starting on the old starter but it was surging on idle, I had to open the throttle plates a lot to keep it running. After less than 50 miles driving, the spark plugs were already black and it died from a flood then wouldn't restart with the 750cfm holley carb on it. The carb was tuned for around 13.2:1 A/F previously with the older parts. Now wouldn't much more open, free flowing intake, heads and exhaust cause the carb to go LEAN instead of going rich?
Carb was originally a 3310s, added 1.5" vent baffles, changed from 6.5 to 8.5 power valve, changed the manual choke to electric, changed the secondary plate to a metering block, holley 110GPH mech. fuel pump with 6 psi regulator. all these mods worked fine before...
Anyways, I switched to the holley HP EFI system, upgraded the fuel pump to a holley 12-920. Getting good pressure and flow from that pump into the TBI (4) 74 lb injectors...still getting a surge happening when the engine turns over enough to start, I think I drained the battery down playing with it idling, charging that now. The engine starts normally, revving up to 1500 rpm for whatever its set time is calculated at, between 7 and 20 seconds...then when it goes past its start mode and into normal idle, its TRYING to keep the RPM between 750 and 900 RPM and ends up surging between 500 and 1100 RPM and the IAC motor is going crazy, I'm watching it on the laptop and it wildly changes from 0 degrees to 35 degrees. Its supposed to read pretty steady at 5-15 degrees. (IAC is the motor that is a TBI's "idle" circuit) The engine doesn't stall out like the carb did but it can't hold a steady idle either. The ignition timing won't idle at the 10-12 degrees advance I originally had the engine and when it goes between 500 and 1100 RPM, the ignition timing is changing at least 15 degrees, I can't tell what the timing is set at now but its going from I think 20 degrees to 35...the timing used to be rock steady moving maybe two degrees at idle. I've got timing gears installed, before my upgrades and they sound normal still.
So...wth is going on with this thing? Did my distributor take a crap on me when the car was parked or should I add more fuel to the idle speeds in the fuel table? I'm going to do a thorough vacuum leak check (again) just to be sure but I'm thinking its my timing, the timing SHOULD NEVER change that much between 600 RPM difference at idle should it....ugh, I'm tired and annoyed, someone please help me out on this one...call an exorcist perhaps?
What is the vacuum at idle speed? The distributor mechanical advance could be right at the point where it's beginning to add advance- this will cause a surge like you describe, unless the ignition advance is electronic. So, what is the timing curve set up like?
Depending on if you're using manifold or ported vacuum for the vacuum advance (if used) can also have an effect on the idle stability.
I'd be suspicious of a vacuum leak- possibly at the intake gaskets, or a malfunctioning PCV valve.
Is the TBI system going into closed loop? If there's a sensor out of range- like the coolant temp, or MAP (if used), etc.- this can throw the system into chaos.
Ok, took a ss of the learn table, I've only had it running at idle and up to 1600 RPM, anywhere its not 0.0 is where the engines been running. The MAP with the engine not running is 102.2 kPa and as you see from the graph, at idle its been going from anywere between 35 and 81 kPa. All numbers are between -3 and 3 so thats supposed to mean that its done its learning under those conditions. 81 kPa = 3.07 inHg based on current atmospheric..35 kPa = 9.75 inHg....ugh yeah, maybe my calc. are out to lunch, I'll have to stick a vacuum gauge on it.
All sensors are showing good values, I watched the CTS, MAT and MAP from initial start through the warmup and the WBO2 sensor is new and the install is good there. Timing curve should be very close to stock. I've got medium weight springs (which worked fine before), normal weights and a stock vacuum advance, when I first built the engine, I bought a new HEI and stuck an accel HEI coil and accel module in it. Still like that. I have no PCV valve. Vacuum when it had the carb on it was showing around 17 inHg.
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