questions about stumble/jerk/hesitation?
06-29-2012, 04:10 AM
#1
Thread Starter
Join Date: Dec 2011
Location: CA
Posts: 21
questions about stumble/jerk/hesitation?
Before you ask, yes I have searched the forums. I've looked and looked and in all honesty alot of the responses I've found, or even the posts are either unrelated or the poster seems to have no idea about whats going on.
What is happening, generally when holding a constant speed the car will "buck". It does not hesitate when accelerating or under load, but instead seems to be when holding a constant velocity. Its seemingly minor, and was actually worse when I had the timing advanced. I attempted running different timing up to 15* and have set it back to 10*. It still has the buck and was actually thinking of retarding it slightly, but that seems counter intuitive. ALSO, I noticed an interesting thing happening with my timing light when the spout connector was connected and removed. When the connector was plugged in and my light was connected it seemed like there was a misfire as the light reacted funny. With the connector out, it strobbed perfectly.
Here's a description of my car, with recent work done in the last year. Next I'll post what is happening, and what I think could be the culprit.
I'm running a stock 86 gt HO 5 speed.
Within the last year these are the following replaced parts/upgrades done:
Fuel Pump, filter, and intake filter/sock
Pressure Regulator
All gaskets including upper and lower intake gaskets, throttle body and egr spacer gaskets
stock 19lb injectors
Air Charge Sensor
ECT Sensor
all vacuum lines
EGR valve
TPS
MAP sensor
all fluid lines
pcv valve and line to intake
cap and rotor
ignition coil
new spark plugs and ACCEL high perf wires
Now here is what II think could the culprit(s)
First, from what I've read it seems like alot of people talk about fuel pressure. In my case, I could understand if it was a fuel problem if the circumstance was happening when attempting to accelerate, but this problem happens at constant throttle. When I have attempted to check my fuel pressure, I get nothing more than about 4-5 psi. Am I supposed to check FP while car is running, or when it is off? With a new regulator, how and why would this be happening?
Also, I have thought about checking TPS voltage ranges as I've read in the past that the TPS shouldn't read OVER a certain number when at WOT. What that number is I have yet to be able to find out again. Does anyone have that so that I can rule out TPS?
Another thing that I have checked is all my lines and plugs, every one of them is within specs and looks a nice chocolate color. No oil, white ash or dark burnt colors. Compression is perfect.
When using scanner the only code that I get is for my MAP sensor, but I cant figure out why that is. I've put on another MAP and get the same code. Its the only code that it blows and wont allow the reader move on to the cylinder balance test.
Ideas? Questions? THANK YOU as always
What is happening, generally when holding a constant speed the car will "buck". It does not hesitate when accelerating or under load, but instead seems to be when holding a constant velocity. Its seemingly minor, and was actually worse when I had the timing advanced. I attempted running different timing up to 15* and have set it back to 10*. It still has the buck and was actually thinking of retarding it slightly, but that seems counter intuitive. ALSO, I noticed an interesting thing happening with my timing light when the spout connector was connected and removed. When the connector was plugged in and my light was connected it seemed like there was a misfire as the light reacted funny. With the connector out, it strobbed perfectly.
Here's a description of my car, with recent work done in the last year. Next I'll post what is happening, and what I think could be the culprit.
I'm running a stock 86 gt HO 5 speed.
Within the last year these are the following replaced parts/upgrades done:
Fuel Pump, filter, and intake filter/sock
Pressure Regulator
All gaskets including upper and lower intake gaskets, throttle body and egr spacer gaskets
stock 19lb injectors
Air Charge Sensor
ECT Sensor
all vacuum lines
EGR valve
TPS
MAP sensor
all fluid lines
pcv valve and line to intake
cap and rotor
ignition coil
new spark plugs and ACCEL high perf wires
Now here is what II think could the culprit(s)
First, from what I've read it seems like alot of people talk about fuel pressure. In my case, I could understand if it was a fuel problem if the circumstance was happening when attempting to accelerate, but this problem happens at constant throttle. When I have attempted to check my fuel pressure, I get nothing more than about 4-5 psi. Am I supposed to check FP while car is running, or when it is off? With a new regulator, how and why would this be happening?
Also, I have thought about checking TPS voltage ranges as I've read in the past that the TPS shouldn't read OVER a certain number when at WOT. What that number is I have yet to be able to find out again. Does anyone have that so that I can rule out TPS?
Another thing that I have checked is all my lines and plugs, every one of them is within specs and looks a nice chocolate color. No oil, white ash or dark burnt colors. Compression is perfect.
When using scanner the only code that I get is for my MAP sensor, but I cant figure out why that is. I've put on another MAP and get the same code. Its the only code that it blows and wont allow the reader move on to the cylinder balance test.
Ideas? Questions? THANK YOU as always
06-29-2012, 05:10 AM
#3
4th Gear Member
Join Date: Jul 2009
Location: Arizona
Posts: 1,127
As for TPS voltage, it should be between .90-.99. Check the line going to the MAP sensor and the connection. If you still get the code, try using an OEM map sensor to see if it goes away.
As for fuel pressure, you should check it while it's running and vacuum is off. If it's FI, fuel pressure should be between 40-43psi with vacuum off and 35-40psi with it on, I believe.
As for fuel pressure, you should check it while it's running and vacuum is off. If it's FI, fuel pressure should be between 40-43psi with vacuum off and 35-40psi with it on, I believe.
06-29-2012, 08:28 AM
#4
Thread Starter
Join Date: Dec 2011
Location: CA
Posts: 21
I understand what the tps is supposed to be set at with butterfly closed. But i'm talking about at wide open, there is a range that it shouldn't exceed. And f'in a, if psi is supposed to be that high then I believe I have found my problem....wow. Thats silly. I have an OEM map sensor, that is what I have compared it to. It still does the same code. I've traced the wiring and it all looks fine. I'm curious if its something with a grounding issue perhaps. But all the wires are exactly as they should be
06-29-2012, 09:43 AM
#6
2nd Gear Member
Join Date: May 2012
Location: NY
Posts: 482
I know you said you checked it. Take a closer look at the rings. A cracked ring will do the same thing. I found this out the hard way many years ago. That is the exact same thing mine was doing (pick up truck). That was the exact word I used back then as well (buck). Not all the time either. Like a couple or 3 times a week.
Sorry, I can't remember what ring it was. The entire thing was an ill experience.
Sorry, I can't remember what ring it was. The entire thing was an ill experience.
06-29-2012, 09:55 AM
#7
6th Gear Member
Join Date: Nov 2006
Location: Spfld, MA
Posts: 9,240
My 89 had a bucking problem @ constant cruising speeds. Check engine would momentarily illuminate during it. Turned out to be the EGR position sensor. It wasn't bad, it was EGR carbon buildup that was slightly pressing on the pintle of the position sensor, causing inaccurate readings. PCM tried to compensate for the mixup between expected O2 readings and actual O2 readings caused by not being able to determine EGR position = bucking.
Last edited by mattdel; 06-29-2012 at 09:58 AM.
07-01-2012, 11:52 AM
#8
2nd Gear Member
Join Date: Jul 2009
Location: NJ
Posts: 189
All of these suggestions, and nobody's mentioned the TFI module on the side of the dizzy....
With the SPOUT connector out, the TFI module generates a spark at 10 deg fixed advance. This is for setting the base timing. The computer advances the spark when the SPOUT connector is in. The computer sends a logic-level signal to the TFI module, which controls coil dwell and all that jazz on its own. TFI's are known to overheat over time and go bad. These things get replaced like bandaids on the bottom of your foot.
Try the TFI module. If you're still having problems, it could also be the hall sensor inside the distributor. I had a fluctuating voltage problem in my stang last year, and after replacing every other ignition component, including the TFI module, I ended up replacing the dizzy itself and it fixed the problem. It was the hall sensor.
With the SPOUT connector out, the TFI module generates a spark at 10 deg fixed advance. This is for setting the base timing. The computer advances the spark when the SPOUT connector is in. The computer sends a logic-level signal to the TFI module, which controls coil dwell and all that jazz on its own. TFI's are known to overheat over time and go bad. These things get replaced like bandaids on the bottom of your foot.
Try the TFI module. If you're still having problems, it could also be the hall sensor inside the distributor. I had a fluctuating voltage problem in my stang last year, and after replacing every other ignition component, including the TFI module, I ended up replacing the dizzy itself and it fixed the problem. It was the hall sensor.
07-01-2012, 03:49 PM
#9
6th Gear Member
Join Date: Nov 2006
Location: Spfld, MA
Posts: 9,240
All of these suggestions, and nobody's mentioned the TFI module on the side of the dizzy....
With the SPOUT connector out, the TFI module generates a spark at 10 deg fixed advance. This is for setting the base timing. The computer advances the spark when the SPOUT connector is in. The computer sends a logic-level signal to the TFI module, which controls coil dwell and all that jazz on its own. TFI's are known to overheat over time and go bad. These things get replaced like bandaids on the bottom of your foot.
Try the TFI module. If you're still having problems, it could also be the hall sensor inside the distributor. I had a fluctuating voltage problem in my stang last year, and after replacing every other ignition component, including the TFI module, I ended up replacing the dizzy itself and it fixed the problem. It was the hall sensor.
With the SPOUT connector out, the TFI module generates a spark at 10 deg fixed advance. This is for setting the base timing. The computer advances the spark when the SPOUT connector is in. The computer sends a logic-level signal to the TFI module, which controls coil dwell and all that jazz on its own. TFI's are known to overheat over time and go bad. These things get replaced like bandaids on the bottom of your foot.
Try the TFI module. If you're still having problems, it could also be the hall sensor inside the distributor. I had a fluctuating voltage problem in my stang last year, and after replacing every other ignition component, including the TFI module, I ended up replacing the dizzy itself and it fixed the problem. It was the hall sensor.
07-01-2012, 08:53 PM
#10
Thread Starter
Join Date: Dec 2011
Location: CA
Posts: 21
The TFI module was actually a source of one of my ideas. With next to everything else top end being replaced, my next idea was the distributor as a whole. I dont want to "rebuild" it as it seems that purchasing all of the parts individually will be just as expensive as purchasing a rebuilt dizzy.
interestingly enough, I purchased an MSD and the stupid thing went haywire. I could never get it to go over 2800 rpms and when it would idle it would freak out. Going up and down like a twitching video thats trying to load online with a bad connection. Took the MSD out and put my stock one back in and it was fine except for the slight stumble at cruising speeds.
I'm on my way to get a egr gasket to check the egr, but I doubt that is the problem. MGMUSCARI, what did you replace your distributor with? I enjoy using Rockauto because of their exceptional warranty and return policies.
OR is there somewhere that I can purchase a STOCK distributor. My brother is a chevy performance mechanic and advised me that unless I'm going to do some serious engine work there are no real gains by putting in a hi perf dizz.
Thanks again
interestingly enough, I purchased an MSD and the stupid thing went haywire. I could never get it to go over 2800 rpms and when it would idle it would freak out. Going up and down like a twitching video thats trying to load online with a bad connection. Took the MSD out and put my stock one back in and it was fine except for the slight stumble at cruising speeds.
I'm on my way to get a egr gasket to check the egr, but I doubt that is the problem. MGMUSCARI, what did you replace your distributor with? I enjoy using Rockauto because of their exceptional warranty and return policies.
OR is there somewhere that I can purchase a STOCK distributor. My brother is a chevy performance mechanic and advised me that unless I'm going to do some serious engine work there are no real gains by putting in a hi perf dizz.
Thanks again
