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Stumble 3000-3500 RPMs


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#1 Ono

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Posted 01 January 2020 - 04:43 PM

Okay this is a looooong story but I'll give you guys the abbreviated version:

I have one of Scott Thompsons computers in my car.  I'll start out by saying that he has been very gracious in offering tips in getting it so it's not doing what this post is all about.

Initially the car had a very bad stumble at 18-2200 RPMs.  No matter what I did it wouldn't go away.  I'd say about 80% of the time it would stumble while driving it.  I eventually grew frustrated (trying to tune it, spinning a bearing in the freshly rebuilt motor, replacing it with another rebuilt motor I had etc)  The fuel tank and system is clean, fuel pressure is great. Injectors are good, new distributor, coil, MSD box etc.

I took the car to a professional speed shop in Wilmington NC where they managed to get the stumble moved up the RPM range to 3000-3500 RPMs.  When they realized that they couldn't get it tuned properly (because they wouldn't send the data logs to Scott or me to forward to him) they pushed the car aside and jerked me around for months before I blew a gasket and went and got it.

Now the car runs worse than it did before I brought it to them.......such is my luck with this car.  When I picked it up they told me they "Didn't Think" it was mechanical (but didn't rule out the possibility) and that it was a computer problem.  I should note that I went and got the computer and sent it to Scott who checked it out and gave it a thumbs up.  

The question is, COULD IT BE MECHANICAL?

I'm going to try tuning it in a next few days with a friend who's a very experienced mechanic and this time the DATA LOGS will be sent to Scott.

Could there me some weird mechanical non computer issue that's causing the problem?  The only reason I ask is, the so called professionals at the speed shop said several times that they don't think it's mechanical, and the computer checked out okay, and the stumble did migrate from 18-2200 to 3000-3500 RPMs.  Maybe it's just something so obvious it's been continuously overlooked.

I know this is a tough question and leaving a lot of detail out.  

Thanks
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#2 markhansenconquest

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Posted 01 January 2020 - 06:22 PM

Have u checked your TPS to see if it has a stumble or glitch...…….Have u rebuild your TBI   ISC idle switch ? if not ,, there full of  old grease (gueee grease wont let it react to throddle changes)....clean and regrease with good grease …...TBI s must be rebuild there no way to get your car to run smooth with out fixing them...…………..I think your problem is the car doesn't see what it wants fast enough ? idle switch must have a  good ground tip contact to work...………( part mech, part elec )………..

Edited by markhansenconquest, 01 January 2020 - 06:38 PM.


#3 Preludedude

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Posted 01 January 2020 - 09:22 PM

If he is running Scott's MS system, he doesnt have a ISC....

Go drive it, and datalog it...It should tell you what is happening when it stumbles....

#4 scott87star

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Posted 02 January 2020 - 10:01 AM

Quote

Go drive it, and datalog it...It should tell you what is happening when it stumbles....

This, since I never got any datalogs I can't diagnose.  A datalog shows everything the ECU is seeing and doing.
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#5 obsolete

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Posted 02 January 2020 - 01:35 PM

View PostOno, on 01 January 2020 - 04:43 PM, said:

I took the car to a professional speed shop...
Now the car runs worse than it did before I brought it to them.
Man, how many times have I seen that story? It's sad. Glad you're sticking with it; given proper data logs, I bet Scott will be able to diagnose it quickly. Good luck!
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#6 Preludedude

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Posted 02 January 2020 - 04:22 PM

View Postobsolete, on 02 January 2020 - 01:35 PM, said:


Man, how many times have I seen that story? It's sad. Glad you're sticking with it; given proper data logs, I bet Scott will be able to diagnose it quickly. Good luck!

Itís so true.  We read this here like once every 6 months.

#7 scott87star

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Posted 03 January 2020 - 10:00 AM

Casey, take a log, its easy.  Connect your computer to the ECU, key on, in Tuner Studio go to the top toolbar, Datalogging.  Click on Start Logging, accept the default time/datestamp filename that appears and you're logging.  Go drive, drive through the stumble, stop the car and go back to Datalogging, click Stop.  That file will be in the datalogs folder in your Tuner Studio Projects project folder (whatever your project was named, default is mycar).  Also do a File, Save Tune As and accept the default time/date filename for the tune file, that will be in the root directory of your project folder.  Email me those two files, you have my email address.
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#8 Ono

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Posted 08 January 2020 - 08:18 PM

View Postscott87star, on 03 January 2020 - 10:00 AM, said:

Casey, take a log, its easy.  Connect your computer to the ECU, key on, in Tuner Studio go to the top toolbar, Datalogging.  Click on Start Logging, accept the default time/datestamp filename that appears and you're logging.  Go drive, drive through the stumble, stop the car and go back to Datalogging, click Stop.  That file will be in the datalogs folder in your Tuner Studio Projects project folder (whatever your project was named, default is mycar).  Also do a File, Save Tune As and accept the default time/date filename for the tune file, that will be in the root directory of your project folder.  Email me those two files, you have my email address.

I've been data logging it the past few days. Right now I'm just trying to get the dang thing to start and run without having coax it to stay running so I can get it out on the road. I've taken it down the road on a couple three or four mile trips scared to death that it'll strand me.  I'll get them to you!

Tell me what you think about this:

When the car was at least semi reliably driving the boost gage always remained in a vacuum and my blow off valve never worked. I'm not sure at what point the car starts boosting but 0-70 through the gears it always stayed below zero on the gage.  I never really paid attention to that as far as fixing it as I was on a time line and more worried about the stumbling problem.  The other day I was messing with things and on a whim decided to eliminate the external waste gate by blocking it off just to see if it was stuck.  I slowly revved the engine up to 3500 rpms and it didn't stutter as bad.  I took it down the road and it did better in the stutter range but still did. As I was trying to watch the road, the AFR, the kPa's on the computer and shift I just focused my attention on the boost gage and feeling the stutter.  For the first time since doing all the work to the car it registered on the boost gage, 3 psi at 70 mph.......and my blow-off valve actually engaged a little tiny bit (or at least it sounded like it did). Now I'm not a turbo guru or mechanic by any stretch of the imagination, but I would think it should be boosting at least 6 PSI at those speeds....shouldn't it?  It got me to thinking that maybe the external waste gate might be some of the problem.  Beside needing the AFR straightened out which is playing a part in it running so poorly, do you think the waste gate being stuck might be part of the issue?

The external waste gate is a Tial....been mounted on the fresh engine I installed after the other one spun the bearing.  It sat for 10 years (Yeah, this car has a loooong sorted story that you wouldn't believe if I told you). So it's not a cheap Ebay one, the blow-off valve is also a Tial with the same mounted on the car/sitting story.  

The turbo is rebuilt also.  There are no vacuum leaks as it's been smoked at least four times throughout the build process.  

At one point the speed shop told me it was making 150 HP on 6 psi and asked me to bring them a MBC so they could turn it up to 8psi for a bit more power. I did two days later and then the car sat never to be touched again. I know this because when I had finally had enough and went and got it, the MBC wasn't installed and I had to ask them where it was.  I brought the MBC to them 3 days after they asked for it and 3 months later is when I went and got the car.

Any thoughts on this?  I'm going to order a rebuild kit of the waste gate even though I just blocked it off and didn't open it up due to wanting to get it out on the road that day.

Edited by Ono, 08 January 2020 - 08:53 PM.

"It's never the wrong time to do the right thing"

#9 scott87star

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Posted 09 January 2020 - 10:27 AM

I think you should email me a datalog of the stumble and the tune file, lets tackle one issue at a time.  You may find them to be related.
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#10 jwmact

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Posted 13 January 2020 - 09:30 PM

Hi Ono,

What is the name of the speed shop in Wilmington? I just had to pull my quest out of shop here in Raleigh (it was there almost 18 months), and it is not running properly. I talked to a shop today in Wilmington, but I want to make sure to avoid another months-long repair.

#11 Preludedude

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Posted 13 January 2020 - 10:03 PM

Stop taking your car from speed shop to speed shop....I guarantee the 2nd shop won't get it right either....

What work are you needing done?

#12 jwmact

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Posted 14 January 2020 - 09:20 AM

View PostPreludedude, on 13 January 2020 - 10:03 PM, said:

Stop taking your car from speed shop to speed shop....I guarantee the 2nd shop won't get it right either....

What work are you needing done?

Need help getting engine/turbo to run properly. Will send PM.




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