RPM Related miss 4600 RPM

[Alaskabuick]

Have been chasing this for awhile on my 87 T. Long Block & Head are Factory stock with exception of 100 lb valve springs.

Basic bolt on build, TE44, 50lb inj, turbo tweak chip, exhaust, THDP, etc.

The miss happens like clock work at 4600-4800 rpm, WOT or NOT. I can stick it in low and give light throttle and run it up to 4600 and it misses, does the same thing at WOT.

Installed new plugs and wires and no change.
Checked coil pack with Caspers coil pack tester.
Checked gap on Crank sensor and seems to be good and not rubbing.

Going to run thru my grounds today just to recheck them.

Hopping someone who has had this issue might be able to shed light on it.

thanks guys,

Dennis

 

[SHADOWII]

Are you showing any knock? What did your plugs show you?
Have you checked the harmonic balancer for cracks/looseness?
What about fuel pressure?

 

[Alaskabuick]

Are you showing any knock? What did your plugs show you?
Have you checked the harmonic balancer for cracks/looseness?
What about fuel pressure?

Plugs looked fine, not bad at all. No knock to mention and like I said it does it when you run up to rpm on light throttle, this is intermittently anywhere after 4600. Now at WOT it seems to just hit the wall at 4650 and will not go past. No popping or back fire, fairly smooth type of bucking.
Ill throw a line on it today and see where the FP is at, fore what it is worth the AF is at high 700's on scanmaster.
Did swap coil pack and Module on another car yesterday, no change.
Checked and reset cam sensor clearance and cleaned the sensor wheel, no change
Relocating and upgrading grounds on head today (although they look good needed to do this anyhow)

I have plenty of donor cars to swap and try parts if need be.

Thanks,

Dennis

 

[SHADOWII]

While you are checking, see if the voltage is falling off at high rpm, or maybe you are hitting the limiter(?) Possibly set too low?

 

[wantattype2]

How old are your valve springs ?

 

[Alaskabuick]

How old are your valve springs ?

Installed last summer comp 980 springs if I remember correctly. They were the 100 lb Lt1 type.

 

[Thumper]

Check your maf numbers, may be hitting a wall.

 

[GNRick]

My car just started bucking at 45 mph . installed new plugs and condition got worse. Turned off alky and no more bucking. Turned alky back on and so far so good.

 

[Alaskabuick]

Check your maf numbers, may be hitting a wall.

Maf when hitting the problem is 255 idle is 6
Funny thing is the car if I slowly bring it up to rpm and hit the miss it sometimes will slowly push past it to 5200 and be fine.
Under load atWOT @ 4650 or so it always just hits a wall.

 

[Alaskabuick]

My car just started bucking at 45 mph . installed new plugs and condition got worse. Turned off alky and no more bucking. Turned alky back on and so far so good.

Well I gave it a try and no change but thanks for the input, maybe this will help me some day in future?

 

[GNRick]

Did you check fuel pressure?

 

[Alaskabuick]

FP good, 60 lb at wot when miss occurs.

Still hit the wall at 4600-4700

However, for some reason the car is no longer missing when I slowly roll it up to rpm with no boost and light throttle (for now anyhow).
Why the change?
1) I did add a direct ground to the negative terminal on Battery to the coil pack, removed grounds from back of head (joy to do) and grounded them to the same post on coil pack mount that it grounded direct to the Battery.
2)I also cleaned the crank ring that signals the crank sensor, had the normal oil residue build up.
3) Changed out serpentine belt, old belt was hammered and had chunks coming out of it, perhaps that was vibrating the crank and throwing off Crank sensor? I doubt it but you never know.

Either I have a intermittent problem that comes and goes under no boost and always during boost or I may of had two seperate issues with similar symptoms at close to same RPM.

Im thinking I should maybe start looking at ramp speed on Alky? Seems to work fine on ramp up but maybe Im going rich on alky at 4600? shot in the dark. .

Think I will drain pump gas and throw in 100 octane and turn off alky to see what happens.

 

[SHADOWII]

FP good, 60 lb at wot when miss occurs.

Still hit the wall at 4600-4700

However, for some reason the car is no longer missing when I slowly roll it up to rpm with no boost and light throttle (for now anyhow).
Why the change?
1) I did add a direct ground to the negative terminal on Battery to the coil pack, removed grounds from back of head (joy to do) and grounded them to the same post on coil pack mount that it grounded direct to the Battery.
2)I also cleaned the crank ring that signals the crank sensor, had the normal oil residue build up.
3) Changed out serpentine belt, old belt was hammered and had chunks coming out of it, perhaps that was vibrating the crank and throwing off Crank sensor? I doubt it but you never know.

Either I have a intermittent problem that comes and goes under no boost and always during boost or I may of had two seperate issues with similar symptoms at close to same RPM.

Im thinking I should maybe start looking at ramp speed on Alky? Seems to work fine on ramp up but maybe Im going rich on alky at 4600? shot in the dark. .

Think I will drain pump gas and throw in 100 octane and turn off alky to see what happens.

Fuel pressure should be increasing 1 for 1 w/boost and outside air temp can effect engine operation when temps start to fall, requiring the reduction of volume. I had an embarrassing moment when the temps dropped in the 40's and the car fell on it's face!

 

[Alaskabuick]

Well I think I nailed it.....and have to give myself a Big "DUUUUUUHHHHHH!"

Timing set is toast, have about 10 degrees of play in crank before cam sensor moves (probably exaggerating). I feel silly that I did not look at this, even knowing that the stock nylon system fails I missed it. Back to basics I guess, my mind got so wrapped around the common issues that are unique to these cars and the electronics that I failed to look at the basics of a pushrod motor.

Will be shocked it this is not the cause of the issue.

Will keep you posted, just ordered a double roller.

Dennis

 

[Nick Micale]

Maf when hitting the problem is 255 idle is 6
Funny thing is the car if I slowly bring it up to rpm and hit the miss it sometimes will slowly push past it to 5200 and be fine.
Under load atWOT @ 4650 or so it always just hits a wall.

This issue has plagued us for a couple years with almost a dozen T-R's, and a recent GN a couple weeks ago had the exact same issue you describe.

We used the TR6 to remedy this problem, check it out here:

http://www.turbobuick.com/forums/threads/tr6-does-it-again.425624/

 

[turbo2nr]

I have similar issue. Car starts and runs great. Good power....until I hit 4900rpm or so.

My theory is the Crank Sensor is loosing signal due to Crank shifting/moving/vibrating just outside the range of sensor.

I think adjusting my crank sensor, or replacing Crank sensor is in my future...?

I say this because I recently had Crank sensor act-up at other times. Braking or turning hard.

I see my signal status on the front of FAST xfi unit. Little LED flashing if signal is present.

??

 

[Fast4Ward]

http://turbobuick.com/forums/threads/fast-loosing-crank-sensor-signal.426261/

 

[turbo2nr]

My problem(s) was corrosion on Ignition plug from the wiring harness-to-Ignition Module and/or bad Buick Ignition Module.

My cure was to clean the plug with electrical cleaner and install TR6 Ignition and modern coil-pack from @TurboBob

Now have full power and rpms. Better starts and idle also!

More stable rpm when I go into gear or cut on A/C.

Did not change my Crank sensor. Now have steady Crank signal, as seen on FAST unit.

Before was starting to get worse and worse with intermittent drop of signal.

Either the Ignition Module or the corrosion?

 

[Alaskabuick]

This issue has plagued us for a couple years with almost a dozen T-R's, and a recent GN a couple weeks ago had the exact same issue you describe.

We used the TR6 to remedy this problem, check it out here:

http://www.turbobuick.com/forums/threads/tr6-does-it-again.425624/

Well Nick , this might be in my future.

I replaced the timing chain that was worn out and figured I nailed the problem... Nope! still missing above 4600 intermittently. Although the car does run smother with new timing chain and was needed.

However, problem still there...

 

[turbo2nr]

Must try a TR6, even if you have to simply borrow One just to prove that you it would solve your issues.

My car is now ripping the tires off as expected after installing the TR6!