408 stroker issues
#42
03-09-2013, 12:22 AM
Legend
Take all this as info from someone who hasn't had a truck in over a year to recall with keen clarity on his own numbers, but on initial look at you numbers I think:
TPS idle voltage is a little low. The lowest good useable voltage I believe is .55v which you are close to. .70-.75v seems to be optimal. Not a deal breaker, but something to monitor due to the next thing:
You described early in the thread a decel problem with your truck. That could be an IAC "counts" problem. Check here for an explanation: http://www.bionicdodge.com/bionic/index.php?topic=11655.0
adjusting the IAC will screw with TPS voltage as well, so reset the PCM after adjusting, and check to see if you moved out of optimal range. I believe the FSM says that .35 is actually OK, but I once bought one sensor in the .40s and it caused the truck to run like crap. Use my info for what it's worth to you.
The next thing I noticed is your upstream O2 sensor swings violently lean and rich, but stays lean for a considerable bit more time in your example. Noting that your short term fuel trims tend to bias more positive numbers and larger positive numbers than negative and the long term trims are leaning positive, the pcm is adding fuel at idle, signifying that your tune is lean at idle. Add a pinch of fuel, as it seems when it tries to push the truck richer on a low lean reading, the long term and sorry term additives are adding up to push it way rich, then it cuts again to go lean. Some of that dance is exactly what it should be doing, but not as wildly as what it currently is. Monitoring fuel trims is one way to evaluate a tune, at least in closed loop. The less short term and especially long term trim adjustment that needs to be done the car the tune is dialed in at that driving condition.
You may also want to speak with your tuner about adding a bit of timing advance as well. It's been a really long time since I had my truck and monitored that information carefully, but I recall my timing at idle to generally be higher than yours. And if I'm not mistaken, aluminum heads need more timing overall as they cool more quickly and the additional timing helps burn the fuel mixture more completely. Adding timing can also hose your engine fast, so defer to your tuner on his recommendation. It won't hurt to ask about it though.
I think your cam is a bit small for that engine. It's essentially a KRC 210 cam with a more relaxed LSA for a wider, flatter power curve. But I really don't think the duration and lift are right to feed those extra cubes. That cam was meant to be a drop in power adder for a bone stock 360. Just eeks under the max recommended lift for stock springs on stock heads, and it has a soft lobe profile compared to other cams. I really think your extra 48 cubes needs more flow in and out. At least 10 more degrees duration at that lift on both intake and exhaust, and a smaller 110 or even 108 LSA will keep the torque as well. Not that a 408 typically needs that kind of help down low.
I don't know what your outside temp was, but 86° at the IAT on a fully warmed up idling not moving engine is good, really really good.
You know already I think the exhaust is a bit too small as well.
TPS idle voltage is a little low. The lowest good useable voltage I believe is .55v which you are close to. .70-.75v seems to be optimal. Not a deal breaker, but something to monitor due to the next thing:
You described early in the thread a decel problem with your truck. That could be an IAC "counts" problem. Check here for an explanation: http://www.bionicdodge.com/bionic/index.php?topic=11655.0
adjusting the IAC will screw with TPS voltage as well, so reset the PCM after adjusting, and check to see if you moved out of optimal range. I believe the FSM says that .35 is actually OK, but I once bought one sensor in the .40s and it caused the truck to run like crap. Use my info for what it's worth to you.
The next thing I noticed is your upstream O2 sensor swings violently lean and rich, but stays lean for a considerable bit more time in your example. Noting that your short term fuel trims tend to bias more positive numbers and larger positive numbers than negative and the long term trims are leaning positive, the pcm is adding fuel at idle, signifying that your tune is lean at idle. Add a pinch of fuel, as it seems when it tries to push the truck richer on a low lean reading, the long term and sorry term additives are adding up to push it way rich, then it cuts again to go lean. Some of that dance is exactly what it should be doing, but not as wildly as what it currently is. Monitoring fuel trims is one way to evaluate a tune, at least in closed loop. The less short term and especially long term trim adjustment that needs to be done the car the tune is dialed in at that driving condition.
You may also want to speak with your tuner about adding a bit of timing advance as well. It's been a really long time since I had my truck and monitored that information carefully, but I recall my timing at idle to generally be higher than yours. And if I'm not mistaken, aluminum heads need more timing overall as they cool more quickly and the additional timing helps burn the fuel mixture more completely. Adding timing can also hose your engine fast, so defer to your tuner on his recommendation. It won't hurt to ask about it though.
I think your cam is a bit small for that engine. It's essentially a KRC 210 cam with a more relaxed LSA for a wider, flatter power curve. But I really don't think the duration and lift are right to feed those extra cubes. That cam was meant to be a drop in power adder for a bone stock 360. Just eeks under the max recommended lift for stock springs on stock heads, and it has a soft lobe profile compared to other cams. I really think your extra 48 cubes needs more flow in and out. At least 10 more degrees duration at that lift on both intake and exhaust, and a smaller 110 or even 108 LSA will keep the torque as well. Not that a 408 typically needs that kind of help down low.
I don't know what your outside temp was, but 86° at the IAT on a fully warmed up idling not moving engine is good, really really good.
You know already I think the exhaust is a bit too small as well.
Last edited by aim4squirrels; 03-09-2013 at 12:27 AM.
#43
03-23-2013, 08:47 AM
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