I just installed a new cam along with the below parts, and now its running like crap. It had a knocking sound (not the rockers or lifers or bearings) which has gotten quiter but is there at higher RPM, and it idles very poorly, lower than normal (below 500). When the RPM dropes below 1000 from mid-upper range it tries to die. Timing has been adjusted (by timing light and by ear) and is right on, fuel pressure has been adjusted and is now at 46psi. I think there must be a vacum leak somewhere... Any ideas?

SLP 206/212 with stock lifters, Cloyes double roller timing chain, adj. fuel press. regulator, MSD wires, Bosch platinum plugs, Accel dist cap, 170 t-stat, and a HP waterpump. Everything else is stock.

91 Z28 305 TPI

[This message has been edited by gregz28 (edited April 24, 2001).]

 

sure sounds like a Vac leak To me.


I dunnoa bout that knocking Tho

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,...

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Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Ive been looking for a leak, but its difficult to pinpoint where its at. Ive tried spraying a carb cleaner and have checked several lines but cant seem to find anything. How can I find this leak?

 

Spray around the intake manifold and ALL over the TPI parts(base,runners, throttle body). You would be surprised as to what you find.

Brendan

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To see the ROC, Check out the webpage Here

 

Actually I did that, and I didnt find anything. The intake is sealed... it has to be somewhere underneth where I cant see or get to.

 

did you adjust the rockers properly?? they dont reallt knock, they will tick annoyingly though if not adjusted properly. another possibility if you have aftermarket rockers (like rollers) is that the bigger cam specs are making the rockers hit the valve covers, but thats not very likely unless you have a large cam...

 

Get a vacuum gauge at a parts store or borrow one. That's a tool everyone should have in their garage. I should help to determin the problem.

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92 RS, 350, Street & Performance MPFI, TFS heads,
Crane Rollers,
MSD Digital 6 Plus, 22lb injectors,
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Hi Flow 3" Cat, stock T-5,
stock rear 3.08, koni yellow adjustable front, twin turbo glass hood, T-tops, Auto Meter Ultra Lite Series 2 5/8 gauges, Teal Green

 

What valve springs are you using?It looks like,from your post,your using the stock heads with the stock springs.If you are you need to install a stronger 1.250 spring.I dont know the lifts for the cam your using,but Im sure it needs a spring stronger than 80# seat pressure.
Another thing to look at is retainer to guide clearance.
Hope this helps,
Nitro Don

 

You might want to drain your oil and check for metal shavings. With a knock thats fadding too a quieter one could be a bad sign that something is amiss. If you find shavings in the oil I would worry about the bad idle right now, I would find out whats knocking. Fix it first then your idle problem will be simple by comparison. If you have a stethiscope you could pin piont the knock or even a vacumm leak very easy.

Steve

 

I adjusted the rockers; its not that because I adjusted them to knock and it was something else. I am using the stock roller lifters, but this is a mild cam that is specifically made to use stock GM lifters and is compatable with the TPI electronic engine controls. The cam is from SLP for 305/350 TPI, 212/206 duration @ .050", .480/.487 lift. The stock springs should be fine with this setup. The same cam was installed on a 305 previously for a short time and there was no problem. I changed the oil and it was fine... The knocking is best described as a baseball card going across the spokes of a bycicle, and can only be heard when I punch the gas.

91 Z28 305 TPI

[This message has been edited by gregz28 (edited April 25, 2001).]

 

Defineitely sounds like a bad roller lifter to me. This of course, is because of the description of the sound (baseball card-spokes..) you mentioned, which is exactly what my engine sounded like when I found out I had a bad lifter after installing my hot cam. Mine, like yours, only made the noise when you get on the gas and rev the engine up. I've made it a point to never reuse stock lifters when swapping a cam on a high mileage engine, no matter what the magazines say about roller lifter engines. Stock lifters need to be replaced from my experience with two tpi engines. I hope this is your problem, in a good way, because it doesn't involve pulling the engine out of the car.

 

i'll second the lifters- i had a motor thathad the same problem myself...

best rule of thumb is to do it right (although not cheap) the first time... the roller lifters are expensive, but you will most likely not have any more noise if you replace them

Steve

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86 Firebird, LG4, t-tops, 2.73 open rear, SLP 3 inch cat back exhaust, catco cat, 1 inch carb spacer, Fiberglass cowl induction hood, Formula wheels, vette servo.

Current Plans: Waiting on: rear end parts- upgrading to 373's, 28 spline axels, slp zexel torsion posi, and a disk brake setup. Also have lowering springs, front struts, and hopefully a new mild 350.


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