lack of top end power, any ideas????
I was even considering selling it. But that wouldnt make much sense after putting so much money into it. I just want it to run right for once! 
06-27-2009, 08:51 PM
#25
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I had to drive the car down the street even with it being hard to shift, on my way back home I pulled it out of third (hard) and whatever was holding it back let go. So for now it seems to be temporarily fixed. I know it probably wont stay fixed but hopefully it will last enough for me to tune the engine.
06-27-2009, 09:05 PM
#26
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Sorry to hear about the trans problems. Maybe it is just the linkage binding?
12psi is a lot of fuel pressure. I would expect it to cause problems at low speed, and not so much at higher RPM. Have you pulled a spark plug to see what they look like? If you get a chance, take one out and look at it. Let us know what you see.
12psi is a lot of fuel pressure. I would expect it to cause problems at low speed, and not so much at higher RPM. Have you pulled a spark plug to see what they look like? If you get a chance, take one out and look at it. Let us know what you see.
06-27-2009, 09:22 PM
#27
how does messing with the timing change your fuel pressure?
fwiw i would first start with the fundamentals, can you check your fuel pressure at w.o.t. ? If the engine isn't getting fuel that will cause your stumble and lack of top end performance for sure. How are your spark plugs, are they a tan color? If they're black and sooty then they are dry fouled from being too cold a heat range. Although expensive, i swear by iridium spark plugs, they fire easier than conventional electrode plugs and would help at high rpm if that's where the problem is. What you can also do first is simply narrow the gap on your plugs 0.005" if they're currently gapped > 0.045".
for the adjustable timing light, what you first do is set the dial to whatever base timing you want. Let's use 10 degree BTDC, so set the dial on 10. With engine at idle, no vacuum advance hooked up, you should read 0 on the timing mark on the crank pulley. As you turn the timing light dial back to 0, the timing illumination on the crank pulley will move towards 10 dBTDC. With base timing set rev engine up to 3000 rpm and illuminate the timing mark on the crank pulley, turn the timing light dial upwards past 20 until you being to see the timing marks illuminated on the pulley. Adjust the dial to illuminate 0 on the pulley, then whatever the dial is at on the timing light is your timing.
i kinda disagree with the exhaust being the problem, a 3" is not too small. Also, if the exhaust is choking the engine then that manifests itself as the engine hitting a brick wall at a certain rpm & load, not a stumble. If the other stuff checks out, then i would look into valve train next, specifically the springs and your lifter preload and seat pressures like was said. At that rpm, springs and valve train as a whole plays a very big part. You mentioned you used the springs that came with the head, the springs should also be matched with the cam & rocker arms.
http://www.chevyhiperformance.com/te...ide/index.html
http://www.compcams.com/technical/FA...lveSprings.asp
fwiw i would first start with the fundamentals, can you check your fuel pressure at w.o.t. ? If the engine isn't getting fuel that will cause your stumble and lack of top end performance for sure. How are your spark plugs, are they a tan color? If they're black and sooty then they are dry fouled from being too cold a heat range. Although expensive, i swear by iridium spark plugs, they fire easier than conventional electrode plugs and would help at high rpm if that's where the problem is. What you can also do first is simply narrow the gap on your plugs 0.005" if they're currently gapped > 0.045".
for the adjustable timing light, what you first do is set the dial to whatever base timing you want. Let's use 10 degree BTDC, so set the dial on 10. With engine at idle, no vacuum advance hooked up, you should read 0 on the timing mark on the crank pulley. As you turn the timing light dial back to 0, the timing illumination on the crank pulley will move towards 10 dBTDC. With base timing set rev engine up to 3000 rpm and illuminate the timing mark on the crank pulley, turn the timing light dial upwards past 20 until you being to see the timing marks illuminated on the pulley. Adjust the dial to illuminate 0 on the pulley, then whatever the dial is at on the timing light is your timing.
i kinda disagree with the exhaust being the problem, a 3" is not too small. Also, if the exhaust is choking the engine then that manifests itself as the engine hitting a brick wall at a certain rpm & load, not a stumble. If the other stuff checks out, then i would look into valve train next, specifically the springs and your lifter preload and seat pressures like was said. At that rpm, springs and valve train as a whole plays a very big part. You mentioned you used the springs that came with the head, the springs should also be matched with the cam & rocker arms.
http://www.chevyhiperformance.com/te...ide/index.html
http://www.compcams.com/technical/FA...lveSprings.asp
06-29-2009, 08:29 PM
#28
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OK, so I adjusted the timing to 15* @ idle and 35* total. I will leave it like this for now until I get some more time to mess with the fuel press. reg.
While I was adjusting the timing I checked out the FP gauge thats in line with the carb and it was now reading 15psi!!! I couldnt get it to go any lower than 12psi by adjusting the regulator.(causing fuel to come out of the fuel bowl adjusting screws) So I wanted to see how it would react if I gave it some throttle. I held the throtttle steady @ around 2K (hwy RPM's) and the FP went down slowly to 2 psi. I tried revving the engine some and the press. went down really fast to almost 0.
So my thoughts are that my fuel pump is just not able to keep up or my regulator is not doing its job. I bought the pump off another 4th gen but I thing it might have been a 6 cyl.
While I was adjusting the timing I checked out the FP gauge thats in line with the carb and it was now reading 15psi!!! I couldnt get it to go any lower than 12psi by adjusting the regulator.(causing fuel to come out of the fuel bowl adjusting screws) So I wanted to see how it would react if I gave it some throttle. I held the throtttle steady @ around 2K (hwy RPM's) and the FP went down slowly to 2 psi. I tried revving the engine some and the press. went down really fast to almost 0.
So my thoughts are that my fuel pump is just not able to keep up or my regulator is not doing its job. I bought the pump off another 4th gen but I thing it might have been a 6 cyl.
06-30-2009, 11:55 AM
#29
if you are revving the engine to 2000-3000 rpm in neutral, then there is no load on the engine and it is using very little fuel... certainly no where near what it would need in gear under load. So you definitely have a fuel delivery problem. In neutral you should be able to bounce it off the rev limiter (or float valves) and your fuel pressure should not change.
But under load at w.o.t. it's not uncommon to only have 1-2 psi of fuel pressure at the carb when there had been 6-10psi at idle.
what kind of fuel pump are you running? Do you have an electrical one in the tank or on the frame rail, or is it a mechanical fuel pump mounted on the engine?
But under load at w.o.t. it's not uncommon to only have 1-2 psi of fuel pressure at the carb when there had been 6-10psi at idle.
what kind of fuel pump are you running? Do you have an electrical one in the tank or on the frame rail, or is it a mechanical fuel pump mounted on the engine?
06-30-2009, 03:52 PM
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Its an in tank pump off another fourth gen. I have one off of a 94 z28 also but the sender doesnt work on it. So bought gas tank with good sender in it and I just swapped tanks. But the thing is that it might have come out of a 6 cyl camaro.
Heres a link to the regulator I have and how it is hooked up.
http://www.holley.com/data/Products/...199R7914-3.pdf
I have it hooked up like "Figure 1" It used to be hooked up like "option A" but then my FP gauge didnt even register any pressure even while the engine was runnning.
Heres a link to the regulator I have and how it is hooked up.
http://www.holley.com/data/Products/...199R7914-3.pdf
I have it hooked up like "Figure 1" It used to be hooked up like "option A" but then my FP gauge didnt even register any pressure even while the engine was runnning.
07-06-2009, 12:16 AM
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So I got around to installing the fuel pump and I now have a steady fuel pressure. The regulator was set @ 3psi and I was too tired to mess with it after swapping the pump out by myself(major PITA btw) Good news is that it holds the pressure even at high rpms even though its in neutral. It does surge up to about 6 psi sometimes though.
I took it out for a test drive and theres no more popping at the top end but it does loose some power at about 5K but it picks back up if I stay in it. Im assuming that now my issues are adjusting the pressure and then maybe playing with the timing some more.
Thanks for your help guys...It has come in very handy.
I took it out for a test drive and theres no more popping at the top end but it does loose some power at about 5K but it picks back up if I stay in it. Im assuming that now my issues are adjusting the pressure and then maybe playing with the timing some more.
Thanks for your help guys...It has come in very handy.
07-10-2009, 11:11 PM
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Finally for some good news. I was driving around today in the 100* weather and the car was running a little hotter than normal. Usually it runs at about 190* but because of traffic it was at a hair over 210* Ive always been uncomfortable driving it hard when it is at this temp nut there were some idiots messin with me at the light so I sped off at the light. When I did this I noticed the sputtering completely disappeared
I found this a little odd because just a few hours before It was sputtering a lot. Anyway, I took it up to 6K in 2nd(close to 75mph) with no hiccups at all. I thought it was just by chance but I tried it several times after that and it ean great.
Could it be that its been running too cold this whole time? or maybe I need better spark plugs. Ive been running it w/out a thermostat b/c my last one seized up on me while driving and I just havent gotten another one.
I found this a little odd because just a few hours before It was sputtering a lot. Anyway, I took it up to 6K in 2nd(close to 75mph) with no hiccups at all. I thought it was just by chance but I tried it several times after that and it ean great. Could it be that its been running too cold this whole time? or maybe I need better spark plugs. Ive been running it w/out a thermostat b/c my last one seized up on me while driving and I just havent gotten another one.
