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Under the seat, CEL by the DLC
I really hope someone spots this that can help me. I know it's not a third gen but it's out of one. One of my customers just bought this 40 ford pickup with a TPI swap that never ran right. It ran very rich and and had a very high idle the firs time I worked on it. Found a slim spacer glued to the throttle bracket for a higher idle and removed it. Unplugged the 9th injector set the timing, cleaned the throttle body, replaced the o2 sensor and its running cleaner now. But it's idling around 700+ and goes in gear to hard, turn it down a little and it stalls way to easy. I really need help with what vin I can put into my scanner to tap into the computer in the morning to get some data out of it in the morning. We have never seen the truck run right and it looks like the PO put in a new IAC. Any suggestions or advice is very appreciated.
The engine is supposed to be and a appears stock. Right down to the ceramic coated third gen exhaust manifolds. Even has a third gen exhaust system. He was told it was 86 350, but I went into my component testing with my newer scanner 5.7 was not an option. I've borrowed a older scanner this weekend to look at data but have no vin.
The only '86 350 as a standard option was in a Corvette. There are rumors that some late '86s may have had a 350, but those have never been well documented.
The AKFP PROM appears to be from a 1988 LB9 (305).
Once you connect and can read data, you may discover that the target idle RPM is 700. There are adders and modifiers depending upon conditions and inputs, of course. If you find that the target idle is lower and the IAC steps are very low, start looking for intake/inlet leaks, including the EGR and PCV. I do know that in some versions of the LB9/auto trans PROMs the target idle is around 700 RPM in PARK. Once the transmission selector is moved that target should drop to the "desired RPM in Drive" parameter.
Another thing which is not helping is that the air inlet is at about the hottest part of the engine compartment. As long as the IAT is in an acceptable range that may no matter a lot,but it is not optimal.
So I can't get data or codes out of the computer, don't know if it's the scanner or the car. I have a bolt meter and had .58 at the tps idleing at 940. Turned down the throttle and now .50 at 690-710. Still feels like it might stall but it's storming and I don't want to make a mess of this guys truck. Still hits in drive and reverse a little to hard. If it had a shift kit maybe the low reverse band hits to hard?
It's fourth gen corvette. Just test drove it, drives nice but goes in gear to harsh. The idle is pretty low so I'll talk to my tranny guy this week. I'll have to get it back next weekend I need my garage back. Had to leave my bird in the rain for the first time sense I bought my house.
I have a fully built trans with very hard drag race shifts at mid throttle on up and even at 1000 RPM the reverse/drive engagement isn't what I would call harsh. It's firm no doubt, but not violent. At 1500 RPM cold start idle it's violent - will chirp the tires on my garage floor. But at 1000 or less it's fine and at 700 it's cute fuzzy puppy.
Off topic - I've done coil overs on those vette rear ends and the easiest way to get that silly fiberglass transverse leaf spring out is to cut it with a sawzall. Seriously I've done that to a $100,000 vette.
GD
Last edited by GeneralDisorder; Jul 30, 2017 at 11:06 PM.
Does your trans have a stall converter? I thought about recommending a converter to this guy but I put one in my c10 a while back and it made the truck take off super slow. I put it in with a trans another mechanic gave me free so I didn't know it was the converter holding it back for over a year. Gave my tranny guy a ride and he told me it was the converter, put in a stock one and now it takes off like a bat outta hell with this vortec engine. Thanks to everyone for the help I might be back here next Saturday with it, hopefully with some scanner data.
Mine has a 3000 RPM stall converter without a lockup clutch (non locking). I also have a 3.70 final drive. It's anything but slow. It lights up tires and chirps second with a stock LB9.
I don't know what happened with your C10, but generally if you want performance you want to move the stall speed of the converter closer to the peak of the power band. Could be that your truck engine makes lots of low end torque but it dies off up where the old converter was stalling.... of it could have just been a crap converter.
GD
Last edited by GeneralDisorder; Jul 31, 2017 at 11:52 PM.
Never thought a little stall speed would hurt. Did some reading after the new converter and was surprised with the theories on choosing the proper piece. I have a Hugh's 4l80 with controller for the c10 and now I'm afraid to use the stall converter that came with it.
Basically the converter is chosen by the power band of the engine and the intended purpose of the vehicle. If you want to burn tires off quickly then you get that stall speed up closer to peak power band. That way when you punch it the RPM climbs to peak power, the converter stalls there, and the wheels get hammered with lots of HP's.
