surging while cruising

O

obrut

Member
Joined
Jun 1, 2001
My 87 T seems to have a real light surge while cruising. I can really notice it in 4th at about 50mph.
Last night I was cruising at 50mph and it was surging, I left off the gas and then gave it about 1/4 throttle and it sounded like it back fired a little then it took off. It wont backfire any other time but right after cruising and then jumping on the gas.

vacuum is 18 at idle
fuel pressure is 45 with the line off
I'll have to try and get my scanmaster readings while it happens

Any simple things that I can check?
 
Have you checked your maf sensor? Check cam sensor also, you can start the car unplug the cam sensor and see if the problem stops. If you do this don't forget to replug in the cam sensor when you are done or car will not start if shut off.
 
I unplugged the cam sensor after it was running and it seemed to make the surging worse.
I did the tap test on the maf and nothing happened.
I turned the fuel pressure up to 50 with the line off and still had the same problem
I turned the fuel pressure down to 40-42 with the line off and still had the same problem. ( I set the FP back to 44-45 with the line off)
The EGR has been ground down and welded closed on the inside of the intake. The vacuum lines have been pluged and my chipped should be burned for no EGR.
I have replaced all of my rubber vacuum lines, and check values. The fp pressure holds when the car is shut off.

My combo is TE44, 210/210 roller, stock intercooler with big neck, 42.5 lb injectors, walbro fuel pump/hotwired and a turbo tweaked street chip - stock trans with rebuild and D5 - stock rearend
 
I pulled all of the plugs and here is what they look like.
IMAG1183.jpg
IMAG1184.jpg


They all look the same, these plug have about 800 miles on them, they are R43TS A/C Delcos.
I ohm my plug wires and they are all between 3.5k and 4.2K
Unplugging the cam sensor made not change
MAF tap test does nothing
All new vacuum lines and check valves
No EGR and chip is burned for no EGR - vacuum lines plugged, hole in intake welded close
Bad surging in 4th locked up at 45mph, almost seems to load up with fuel because I will get a pop or backfire after cruising and then hitting the gas.
At idle the car is smooth, if I hit the gas in park sometimes I get a pop.
Is there anything else that I can check?
 
I changed the gap on the plugs from a tight .032 to .035
I ohm the coil packs out all were around 12.6k
Verified and adjusted the tps to .42 - 4.64 key on engine off
*Test drive: surging almost completely gone but I can still feel a little surging/bucking only at light throttle in 4th at 45mph. Idle is a lot smoother too.

Dropped fuel pressure from 45 to 42-43 psi line off
WOT blast = 14-15 pounds of boost with O2s at 789, did a WOT blast twice with the same results.

At 45mph in 4th locked up here are my scanmaster readings,
AF 36
L8 129
BAE 14.2
INT 123
BLM 123
MPH 46
CLE 162
AES 75
RPM 1450
TPS .92
IAC 82

Here are my scanmaster readings at idle hot
AF 05
L8 34
BAE 13.7
INT 128
BLM 132
CLE 165
AES 89
RPM 750-800
TPS .44
IAC 31

I also touched the brakes to unlock the converter and I can feel it unlock and when I left off the pedal it locks again. It is definitely not locking and unlocking.

Any thoughts?
 
The three plugs on the right are way lean. The three on the left are burning good. I would check fuel Injectors on whatever side the three on the right came out of or your fuel rail. I would start there because seems to me that side is not getting enough fuel. Just my 2 cents.
 
Hotrodbuick said:
The three plugs on the right are way lean. The three on the left are burning good. I would check fuel Injectors on whatever side the three on the right came out of or your fuel rail. I would start there because seems to me that side is not getting enough fuel. Just my 2 cents.
Click to expand...

its just a bad camera angle, they all look the same.
 
They all look lean and that would cause a cruise surge. Should send your chip in for an update.
 
I am experiencing pretty much the same thing...at cruising speed 50-55 it will surge and then buck pretty bad, feels like it shifts in and out of gear and occasionally backfire. Usually happens after +/- 20 minutes of driving but not all the time. All my problems started about 2 weeks ago and at some point during the bucking and surging my belt peeled off a couple ribs. I had the defroster on and found out my compressor was cycling on and off and possibly seizing up causing the belt to shred? Replaced the belt and it did it again...unplugged the compressor to stop the constant cycling and hoped that was at least part of the problem...drove to work this morning and the belt is OK but it did surge/buck again some with a small backfire after about 20 minutes of driving however it was not nearly as bad as it was before when the compressor was plugged in.
 
I had the same surge and after searching the forum I found a post suggesting turning the cam sensor just slightly counterclockwise. It worked for me, don't go to far just a 1/4 inch of movement was all it took.
 
John, I'm running a turbo tweak chip thats only about 2 years old and is programmed for my current combo. If I send it in for an update what would be done?

Scott89TTA and 84sithlord I see both of you are running 60 pound injectors with turbo tweak chips I have 42.5 pound injectors. My injectors were something on my list to check but if you guys have the same problem with different injectors that kind of reduces the chance that they are the problem.

Vince I think I remember reading something similar, any insight as to why a 1/4 turn made a difference? Does it have something to do with the larger cam? I'm running a 210/210 roller
 
Are you sure it's not the l/u solenoid going weak/bad? It engages at 45-50 mph. Try driving it in 3rd gear and see if you have any change.
 
SHADOWII said:
Are you sure it's not the l/u solenoid going weak/bad? It engages at 45-50 mph. Try driving it in 3rd gear and see if you have any change.
Click to expand...

When its surging if I touch the brakes and hold the pedal just enough to unlock the converter its still surging. When I left off the brakes I can feel the converter lock and of course the surging is worse.
 
3rd gear will eliminate the computer signal to the sol. and if you have a means of monitoring your fuel pressure at speed, you should be able to eliminate a pump problem. Have you ck'd for and cleared any codes?
 
obrut said:
John, I'm running a turbo tweak chip thats only about 2 years old and is programmed for my current combo. If I send it in for an update what would be done?

Scott89TTA and 84sithlord I see both of you are running 60 pound injectors with turbo tweak chips I have 42.5 pound injectors. My injectors were something on my list to check but if you guys have the same problem with different injectors that kind of reduces the chance that they are the problem.

Vince I think I remember reading something similar, any insight as to why a 1/4 turn made a difference? Does it have something to do with the larger cam? I'm running a 210/210 roller
Click to expand...

It's not a 1/4 turn, just very slightly move it a 1/4 inch. I must have had it set on the edge of the window of operation, I had moved it too far and created a pig rich cold start condition that took me a while to figure out. Good question about the cam, I wish I would have stayed with the stock cam however I was talked into the larger cam by the engine builder so I could grow into the combo.............dumb I know but live and learn.
 
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