Jumpy tach after blower install
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Jumpy tach after blower install
After my blowers been in, I've noticed my RPM tach is very jumpy under WOT. What could cause this? I have a rev limiter in (MSD pill)set at 5500, and one in the PROM at 6200.
But the tach starts acting funny past 3k...
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91 Formula
305 TPI 5speed
1LE/G92/WS6
Paxton SN92 polished kit, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL,MSD boost-master,Holley 9mm wires,Ac delco R43ts plugs,custom chip,Ford SVO 24# injectors,Bosch O2sensor, Bosch in-line pump(w/stock pump), SLP 1 5/8" headers,SLP catback,short shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
But the tach starts acting funny past 3k...
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91 Formula
305 TPI 5speed
1LE/G92/WS6
Paxton SN92 polished kit, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL,MSD boost-master,Holley 9mm wires,Ac delco R43ts plugs,custom chip,Ford SVO 24# injectors,Bosch O2sensor, Bosch in-line pump(w/stock pump), SLP 1 5/8" headers,SLP catback,short shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Senior Member
Joined: Nov 2000
Posts: 727
Likes: 1
From: Charleston, WV, USA
Car: '86 IROC-Z + Misc. project cars.
Engine: Supercharged + Nitrous TPI 355 CID
Transmission: Art Carr built Th700r4
You might have some misfire or crossfire.
higher cylinder pressure makes sparking the plug more difficult. It drawns higher amperage through the plug wire. The higher current can induce a voltage in the adjacent wire. Also the higher resistance at the plug gap makes it easier for the spark to jump to a ground or crossfire to another plug wire.
Check your plug wires for damage & check their routing. It is important to keep them separated as much as posible. You should never run wires from adjacent cap terminals parallel with each other. They should be kept as far apart as posible with other wres in between.
Cylinders 5 and 7 on the left side and cylinders 4 and 8 on the right side are the four you have to watch most. This is because they follow each other in the firing order and are on the same side of the engine.
Route the plug wires in their harness in this order:
Right hand side › 4-6-2-8
Left hand side › 7-3-1-5
You might also have your plugs gapped too wide. You might have some mild carbon tracking in the distributor cap too. Sometimes, if the resistance at the gap is very high the coil can arc to ground also.
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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"
EFI Performance Club on Yahoo
Club IROC-Z
[This message has been edited by IROCKZ4me (edited February 26, 2001).]
higher cylinder pressure makes sparking the plug more difficult. It drawns higher amperage through the plug wire. The higher current can induce a voltage in the adjacent wire. Also the higher resistance at the plug gap makes it easier for the spark to jump to a ground or crossfire to another plug wire.
Check your plug wires for damage & check their routing. It is important to keep them separated as much as posible. You should never run wires from adjacent cap terminals parallel with each other. They should be kept as far apart as posible with other wres in between.
Cylinders 5 and 7 on the left side and cylinders 4 and 8 on the right side are the four you have to watch most. This is because they follow each other in the firing order and are on the same side of the engine.
Route the plug wires in their harness in this order:
Right hand side › 4-6-2-8
Left hand side › 7-3-1-5
You might also have your plugs gapped too wide. You might have some mild carbon tracking in the distributor cap too. Sometimes, if the resistance at the gap is very high the coil can arc to ground also.
------------------
Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"
- 355 cid
- AFR heads
- Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
- modified SLP runners
- TRW forged pistons/ceramic coated
- fully balanced
- Edelbrock headers/ceramic coated
- SLP cat-back
- Paxton supercharger
- Nitrous Express nitrous oxide
EFI Performance Club on Yahoo
Club IROC-Z
[This message has been edited by IROCKZ4me (edited February 26, 2001).]
Senior Member
iTrader: (3)
Joined: Jul 1999
Posts: 844
Likes: 0
From: Long Island, NY
Car: 1987 GTA
Engine: 645hp/656 ft lb Blown 383
Transmission: 700-R4 3,000 stall
Axle/Gears: 3.55 moser 12-bolt
may sound silly but, do u have a custom PROM? you may need one
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SUPERCHARGED 87 GTA: Blk/Gld w/Superam, 355cid Trickflows, forged pistons 9.5:1. Auto 2,600 stall, 3.45 9 bolt disc, Best time & mph (Naturally Aspirated): 13.567 @ 101.900 w/ a poor 60ft. Best mph: 104.3 *This car is 100% NYS emissions legal, w/ all emissions controls!* "If you want to have a fast car, hang out w/ those who do!"
http:// www.community.webtv.net/munks87/JustinsGTApage.com
VORTECH S-TRIM, INSTALLATION IN PROGRESS: 10 & 15 LB> PULLEYS, CUSTOM HKS RACE BYPASS, CUSTOM DUCTING W/ COLD AIR, SWAPPING TO SERPENTINE, & MANY EXTRAS! BEST TIME: 11'S I GUESS. WE'LL SEE IN SPRING!
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SUPERCHARGED 87 GTA: Blk/Gld w/Superam, 355cid Trickflows, forged pistons 9.5:1. Auto 2,600 stall, 3.45 9 bolt disc, Best time & mph (Naturally Aspirated): 13.567 @ 101.900 w/ a poor 60ft. Best mph: 104.3 *This car is 100% NYS emissions legal, w/ all emissions controls!* "If you want to have a fast car, hang out w/ those who do!"
http:// www.community.webtv.net/munks87/JustinsGTApage.com
VORTECH S-TRIM, INSTALLATION IN PROGRESS: 10 & 15 LB> PULLEYS, CUSTOM HKS RACE BYPASS, CUSTOM DUCTING W/ COLD AIR, SWAPPING TO SERPENTINE, & MANY EXTRAS! BEST TIME: 11'S I GUESS. WE'LL SEE IN SPRING!
Thread Starter
Banned
Joined: Jul 2000
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The MSD box never gave me problems before and has always worked great. I don't think it could be that....but maybe
I run Ac Delco R43TS gapped at .035
My chip is custom for my blower and 24#ers.
The wires are brand new and I have like a ton of wire separators on them to make sure they do not touch each other. The cap and rotor are new as well. I am really dumbfounded on this one
thanks for the replies guys.
I run Ac Delco R43TS gapped at .035
My chip is custom for my blower and 24#ers.
The wires are brand new and I have like a ton of wire separators on them to make sure they do not touch each other. The cap and rotor are new as well. I am really dumbfounded on this one
thanks for the replies guys.
Senior Member
Joined: Nov 2000
Posts: 727
Likes: 1
From: Charleston, WV, USA
Car: '86 IROC-Z + Misc. project cars.
Engine: Supercharged + Nitrous TPI 355 CID
Transmission: Art Carr built Th700r4
I still believe it's crossfire when under boost/load! but you might want to swap back to your other PROM to see if it goes away. I once had a PROM go bad and it caused the tach needle to jump & twitch at 2000 RPM at part throttle cruise.
If it is indeed crossfire under load, sometimes removing the MSD can make it go away. This is because removing the MSD takes away alot of the ignition systems energy anad it just doesn't have enough @$$ to jump spark far enough to crossfire.
As I said in my other post the big culprits are usually 5&7 and 8&4. If they are run side be side in the loom they can still crossfire or induce a voltage in each other even if spaced far apart. The coil can jump a spark to ground too. A small amount of carbon in the cap or even a small amount of moisture can cause this problem when under load but not show itself when not under load.
You could have one or more bad plugs. Your gap seems like it should be ok but it wouldn't hurt to try tightening it up and seeing if it helps. Try 0.030" to see if there is a difference. This willmake it easier to spark. If it does run better without the needle twitch then that proves it is crossfire.
another minor possibility is that it is running at the edge of being too lean.
------------------
Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"
EFI Performance Club on Yahoo
Club IROC-Z
[This message has been edited by IROCKZ4me (edited February 26, 2001).]
If it is indeed crossfire under load, sometimes removing the MSD can make it go away. This is because removing the MSD takes away alot of the ignition systems energy anad it just doesn't have enough @$$ to jump spark far enough to crossfire.
As I said in my other post the big culprits are usually 5&7 and 8&4. If they are run side be side in the loom they can still crossfire or induce a voltage in each other even if spaced far apart. The coil can jump a spark to ground too. A small amount of carbon in the cap or even a small amount of moisture can cause this problem when under load but not show itself when not under load.
You could have one or more bad plugs. Your gap seems like it should be ok but it wouldn't hurt to try tightening it up and seeing if it helps. Try 0.030" to see if there is a difference. This willmake it easier to spark. If it does run better without the needle twitch then that proves it is crossfire.
another minor possibility is that it is running at the edge of being too lean.
------------------
Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"
- 355 cid
- AFR heads
- Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
- modified SLP runners
- TRW forged pistons/ceramic coated
- fully balanced
- Edelbrock headers/ceramic coated
- SLP cat-back
- Paxton supercharger
- Nitrous Express nitrous oxide
EFI Performance Club on Yahoo
Club IROC-Z
[This message has been edited by IROCKZ4me (edited February 26, 2001).]
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