BK

I got my car back today with the new heads and cam and the car is running horribly. I pull up to a stop light and the car wont idle, it goes from almost stall 400 rpms (doesn't stall though) to about 700 rpms and then goes back to 500 ( you get the idea). Its running really rough. I'm calling Performance Resouces tomorrow and seeing about ordering a chip, but I'm having the mechanic go over it again. Is there something I should look for? The cam is a comp cam with S/R torquer 305 heads, fuel pressure is set correctly. Any ideas?

89BlwnRs

It's probably the computer not being able to compensate for the greater amount of air your engine is sucking in. A good custom chip should do the job. . .

Also, if you get a custom chip I'd love to know how those heads worked out. Those are the exact heads I'm looking at putting on my car. I'd also be interested in knowing if you put the cam in while the engine was still in the car. . .

Any help is appreciated,

Jason

Mike92

Play with the TPS, fuel pressure and timing. Yes you would benefit from a custom chip! Also idle your car up to about 1000rpms in neutral might help.

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305TBI FireBird, Holley Intake and TBI, Headers, Torquer Heads, Gears. Best E.T. 15.08 at 92.5, 0-60 6.45.(Before Heads)Summit cam purchased 204-214, to be installed in 350 shortblock "soon" Shooting for 13's, oh yeah!

badbird88

Ever since I put my new motor in..same as putting new heads and cam in your motor, my car never has idled right. It will idle normal some times but most of the time it fluctuates from 500-900 rpm. The stock TBI computer, according to GM themselves, will have troubles (specifically the idle problem your having) with a cam that has a duration bigger than 194 degrees on the intake side. I called around when I first put my motor in my car and got that same explanation from several companies including the GM engineers. I'm curious if the new intake will cure some of that problem. My does it the most before it really gets warmed up good and always if I push the clutch in while the car is moving it will fluctuate up and down. My cam is a LT1 cam which is around a 212-214 degree on the intake side at 0.050".

You could try changing the idle slightly and bumping your timing up to 8-10 degrees if it's not already bumped up. I noticed a much better throttle repsonse when I went from 3 up to 8-9 degrees. I didn't want to go too high for fear of burning a hole in the piston. I left my idle at around 650rpm though and my timing at 8 degrees. The idle doesn't hurt anything but mine doesn't act like it's going to cut off. The chip probably will help. Don't get hypertech, I couldn't tell any difference between my hypertech and the stock chip. If you go with performance research let me know how the chip performs!


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1988 TA 300+hp 350 w/ TBI and Holley TB unit,
WC T-5, 3.42 gears w/ Auburn posi. MSD 6A, edelbrock TES headers, dynomax 3" cat and cat-back system, ACCEL coil, polyurethane bushings all around, aluminum driveshaft, Mr. Gasket open air cleaner.

1993 S-10 w/ 4.3L V6 TBI, slightly bigger cam, Mild polish job and 3 angle valve job on heads, Edlebrock TES headers, Dynomax cat back, MSD 6A, ADS chip
(bought from my dad)

2000 GMC Sierra Regular Cab Stepside
285hp 5.3L w/ 3.42 gears and locking diff. (sold to my dad..no!!)

[This message has been edited by badbird88 (edited September 21, 2000).]

FastBroker

The reason your car(s) won't idle with a big cam is that the PROM has the idle speed set for 525 rpm. An engine with a larger cam than about 204 deg intake will have problems with this and will be compunded by bigger heads/exhaust and free-flowing intake. (Yes, intake will hurt problem) The computer goes into a hissy fit because it cannot get the engine rpm/AFR to stabilize at 525 rpm becasue of fuel and spark mismatches. (plus, big cams just need more idle speed...) You need PROM work to fix idle speed for sure, but Fuel and Spark curves should also need MAJOR tuning. AFPR/spark stuff can help, but they are band-aids for a more serious problem

[This message has been edited by FastBroker (edited September 21, 2000).]