Throttle response

james5275

Registered User
Hello everyone, it's been a while,
90 auto with mild bolt-ons- double IC, raised top, 10% pulley, exhaust, Mac intake. 120,000 miles. Recent maintenance- head gaskets/valve jobs and spark plugs.
I have been wondering for a while about the throttle response from idle of my SC and if it's normal or if there's a problem. The engine puts down plenty of power and doesnt misfire at idle or under load (except for next paragrah). Compared to my blown GM 3.8 the response seems very sluggish. My thoughts are the sluggish response may be due to the IC plumbing and bypass valve, i.e. the nature of the beast. Anybody notice the same with their near stock SC? This is something I only noticed after buying my GM which was about 5 years ago. I'll try posting vids to compare the 2.

One other problem with the car is during cold starts. I remember when it was a low mile car, when starting the engine the rpm's would shoot up to maybe 1500-1700, then gradually decrease like many other vehicles do. Now, when it starts, there is some misfiring for a short moment, and then it smoothes out. Does that make any sense? When warm, it starts normal. My guess is an IAC, but I dont want to throw parts at it. No CEL.
Thanks for looking and happy holidays,
JJ

Car is also throwing a code 49, see below
 
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Same engine

Yes, my olds has the same engine I believe. Funny thing is the GM with no IC only produces about 8 lbs VS the ford with about 15. Bird is much quicker in the 1/8th, but it just doesn't have that "snap your neck" response. I do know that the GM has a higher stall converter. But even in neutral the GM responds better.
JJ
 
Yes, my olds has the same engine I believe. Funny thing is the GM with no IC only produces about 8 lbs VS the ford with about 15. Bird is much quicker in the 1/8th, but it just doesn't have that "snap your neck" response. I do know that the GM has a higher stall converter. But even in neutral the GM responds better.
JJ

I think the supercharged GM 3.8 has a higher CR, either the same or much closer to the NA GM 3.8. There is a big drop in compression from the Ford 3.8 NA to the Ford 3.8 SC. So that might explain the difference in off-boost responsiveness.

You can add an intercooler to the GM 3.8, but you need a custom lower intake and a water-air "brick" IC.
 
Code 49

I cleared codes then drove the car today. After about 20 minuites of driving I shut down and pulled KOEO codes, only code is 49. According to the Haynes, code 49 is default spark error. Any suggestions? New plugs installed at HG replacement about 300 miles ago. Could the coil pack give me the misfiring at start up?
JJ
 
Service Cod 49 indicates the spark timing has defaulted to 10 degrees BTDC. The SPOUT signal has a variable duty cycyle with amplitude that varies from 0.4v to VBAT. In the event of a SPOUT failure, the DIS module will generate a fixed dwell and constant spark angle based on CID and PIP signals (FMEM mode). Possible causes:
- Faulty DIS module
- Faulty SPOUT circuit.

Start with making sure the SPOUT plug is inserted into the connector. This is just a plug inserted into the harness near the DIS module.

In addition mechanical issues, response on the SC might be considered laggy compared to a motor where the throttle plate is closer to the intake manifold. The extra intercooler piping adds significantly to the lag between the call for power, and the actual application of it. Not so much that we really notice it, but if you compared it to one of the SC's with and inverted blower setup, I bet you would notice it.
 
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Thanks for the reply, these things as you know can be very frustrating especially when on a budget. I did search the forums and found a lot of other info on code 49 but no solid fix. One guy even claims a chafing spark plug wire was the cause. Will I need tuning fixtures to 100% identify the source? It drives me nuts to throw parts at macinery.
I'll check the spout plug today and post back with results.
Thanks again,
JJ
 
SPOUT plug

Gave the engine wire harness a basic look over and wiggled wires with no luck. Disconnected all easily accessable connectors, didn't find anything wrong. Pulled the spout plug with the engine running and noticed a momentary drop in RPM, then engine recovered. No noticeable difference when installing the plug. What does that tell us? DIS was replaced about 3 years ago/ 1500 miles with a new one from NAPA. Original coil pack. What sensors relay timing info to the computer?
Sounds like Crank sensor is ruled out since it will start.
 
Clear the codes, then check again.

In the mean time you could use a digital meter to check if any of the contacts in the harness for the spout are shorted to ground. They shouldn't be. Check the connectors on the DIS module and make sure they are all set good. As long as code 49 pops up, you won't get anything other than 10degrees base timing.
 
knock sensor code, running

Pulled KOER codes last night and also showed knock sensor failure, sorry I dont remember the code number. But I will clear and start over. Will also check wiring as suggested. It would make sense to me that timing advancement would be prevented if knock protection isnt available.
So what's on your wish list for Xmas?
JJ
 
Code 25, knock sensor

Cleared codes today and ran another test, I didn't drive it, just allowed it to fully warm up before shutting down and then pulled codes.
Pass for O & C codes, 25 for R, knock sensor not sensed during dynamic test. Sounds like a winner to me, please say it is! I will do a search for code 25 fixes, any other input?
JJ
 
Cleared codes today and ran another test, I didn't drive it, just allowed it to fully warm up before shutting down and then pulled codes.
Pass for O & C codes, 25 for R, knock sensor not sensed during dynamic test. Sounds like a winner to me, please say it is! I will do a search for code 25 fixes, any other input?
JJ

James,

If the knock sensor is unplugged (not sensed) the EEC will command full spark retard which is 8 degrees less than normal timing, and that would make the car feel like a pooch. Might just be unplugged. See this thread for more info.

http://www.sccoa.com/forums/showthread.php?t=111564&highlight=knock+sensor

David
 
code 25 vs. 225

Thank you,
Found that thread last night, read many others about the KS but really no fixes. It would be nice to know the difference between code 25 and code 225 which have the same definition for the KS. I'm hoping the difference is circuit failure vs. sensor failure. I did check last night, it's not unplugged, which would have been great but you know how that goes! I will ring out the wiring for that circuit next and move on from there. Is there anybody else I could PM or contact? Next question is where to find a sensor.....
JJ
 
I think the supercharged GM 3.8 has a higher CR, either the same or much closer to the NA GM 3.8. There is a big drop in compression from the Ford 3.8 NA to the Ford 3.8 SC. So that might explain the difference in off-boost responsiveness.

Supercharged GM motors have 8.5:1 compression, same as 94-95 SC. NA GM 3.8's have 9.4:1.

My stock '94 SC has lousy throttle response :mad:

From my experience tuning GTP's, they have very generous part throttle timing maps.. But then again, a stock GTP takes heavy throttle to get into boost, where the SC seems to cross into boost at light throttle.

Jeramie
 
Thank you,
Found that thread last night, read many others about the KS but really no fixes. It would be nice to know the difference between code 25 and code 225 which have the same definition for the KS. I'm hoping the difference is circuit failure vs. sensor failure. I did check last night, it's not unplugged, which would have been great but you know how that goes! I will ring out the wiring for that circuit next and move on from there. Is there anybody else I could PM or contact? Next question is where to find a sensor.....
JJ

Code 25 is for an 89-90. Code 225 is for a 91-95. I'm not going to look up the actual code so I don't know what it says (that's your job :p), but if you did not tap on the exhaust manifold to generate a knock during the code test, you may get that code. This doesn't mean that the knock sensor is dead, just that you didn't do the test right.

On some years a disabled knock sensor means no knock sensor, and generally all is well. On other years it seems according to the strategy docs that full timing may be pulled automatically causing poor performance. Generally the knock sensor is disabled below 190 deg and vacuum readings from 30-5in HG. So if it were a knock sensor issue, the car would run great when cold, not so great once up to operating temperature.
 
R code procedure

At what point do I simulate knock during the test? I would assume shortly after the TPS check....
 
James,

If the knock sensor is unplugged (not sensed) the EEC will command full spark retard which is 8 degrees less than normal timing, and that would make the car feel like a pooch. Might just be unplugged. See this thread for more info.

http://www.sccoa.com/forums/showthread.php?t=111564&highlight=knock+sensor

David

Is it possible that a malfunctioning KS would prematurely cause the EEC to throw the code 49, which I had earlier? Or is it possible with the mods I actually have knock and timing is getting pulled- hence code 49?

You may not approve of what I did tonight, I removed the KS and secured it away from structure- still plugged in. I'm thinking of taking it for a drive and see what happens. Sounds dangerous doesn't it?

I may have a hook up with the KS. It appears to be nothing more than a velocimeter, which is what we use to balance the propellers on our airplanes. The systems we use are calibrated anually- maybe I can get them to check the accuracy of mine. Our aircraft system measures velocity in inches per second, which may not be sensitive enough for the knock sensor but I'll give it a shot.
JJ
 
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im suprised nobody mentioned it

the sc's are so sluggish at tip in due to overfueling, these things tip in so rich its amazing that they don't stall out and die


step 1 when i tuning any sc is to reduce tip in fuel by 50%


btw our engines don't need much timing, with the spout pulled or the dis locked at 10, you won't notice much of a difference output wise unless you have a bunch of mods done
 
im suprised nobody mentioned it

the sc's are so sluggish at tip in due to overfueling, these things tip in so rich its amazing that they don't stall out and die


step 1 when i tuning any sc is to reduce tip in fuel by 50%


btw our engines don't need much timing, with the spout pulled or the dis locked at 10, you won't notice much of a difference output wise unless you have a bunch of mods done

I've heard that they are factory tuned on the rich side, better safe than sorry I suppose. I have been addressing the ignition problems since those are the codes it's producing. But the mixture does make sense with the starting problems. For the record, I did test all of my injectors at HG replacement recently.
JJ
 
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