1982CorvetteDude

I've been trying to chase a miss in my engine after my TPI swap...I just put the engine on a vacuum guage:

It's showing a reading of 19...but fluctuates between 18 - 19. It doesn't hold a steady pressure at 19.

The book that came with the guage is indicating an ignition problem...that makes sense with my miss, I've replaced everything from the plug wires, distributor, rotor, coil, cap, plugs....everything is new.

The engine is timed at 6 degrees btdc...all wires are routed correctly.

The plug wires are new but leftover from my carb set-up, they are accel yellow universal cut to fit.....it's possible that I could have incorrectly crimped a wire or could have came loose while I was tugging on it. That's the only thing I haven't changed yet since doing my TPI stuff. I'm going to try and order a direct fit set....any suggestions on something can will route under ram horn manifolds nicely?

Everything else on my TPI is brand new, all sensors ect. So I'm think it's the plug wires if that's what my guage reading indicates.

Now my other question.....I have a weird stumble / jerking from the engine at cruising speeds..the engine startes bogging erratically..could a ignition problem cause that? I can drive about 40 - 60 mph and let off the gas or barely let off and the car starts jerking erratically....but the minute I give it accelerate and get the RPM's up it quits....only to start back again when I let off.

Keep in mind I didn't have this issue when I had the carb set-up, it actually cruised nicely..

I did a vacuum test at 2000 rpm's and it jumped up to about 25ish and held steady pressure....no fluctation.

Any ideas?

P.S. I have asked questions in the C4 Tech section about other stuff....I found out there are a few smart-azzes there....so I'm hoping to get advice here....that place can be borderline off-topic sometimes.

BarryK

try this link
at the bottom of the page there are various senarios to help you detrmine what a problem may be based on how the vacuum gauge reads and acts.

http://www.secondchancegarage.com/public/186.cfm

MILO

Can't help on the TPI stuff, being a carb man myself. However, I've found a lot of my misses through hooking up a timing light and check each wire as someone ran the engine up to cruise rpm. I've found bad wires to cracked insultors on plugs this way. Also pulling each wire off one at a time to see if there was a dramatic difference in the engine idle, little or no change, I would investigate that cylinder. The other way is to use a can of carb cleaner and spray it around any connection that was connected to the manifold, looking for a manifold leak.

Good luck.

1982CorvetteDude

Cool site, mine looks like scenerio 11...except the needle starts at 19 and moves back and forth between 19-18.

I'll try moving my timing and see what happens.

1982CorvetteDude

I'll try that, I hope I don't have a manifold leak Lot of stuff to remove.

BarryK

have you set up the idle fuel mixture first using the vacuum gauge?
I'd do that and than see what kind of readings the gauge gives you.
just hook the gauge to a full manifold vacuum source (not a ported vacuum source) and adjust your mixture screw(s) to give you the highest steady vacuum at idle.
After that see if there is any difference

langlj00

Definately sounds like too much vacuum advance.

If you are set up to get 36Deg max mechanical timing and the additional vacuum advance takings you over 52Deg, then you may well get the symptoms you mention.

If your vacuum advance can is providing more than 16 Deg advance then this is too much. It might be that your old carb set up had lower vacuum than 19" and it didn't pull the full advance but now you are leak free you are getting just that bit too much.

When you open the throttle the vacuum signal disappears so this problem only occurs as you let off.

If you can't adjust your vacuum advance canister, then try setting the curb idle to say 4 Deg and taking a drive (I don't suggest you leave it at 4 - just try it - since you will have backed off the total by 2 degs.)

If that works you need to get an adjustable vacuum can.

Jeremy.

1982CorvetteDude

I haven't done that yet, I tried to set it with the Tach, I'll try that tonight..

1982CorvetteDude

That makes sense, one question...I don't have a vacuum can on my distributor....the advance is handled by the ECM

1982CorvetteDude

Another thing I noticed…it seems like my engine is “shaking” more than it did with the carb set-up….everything on the front end is vibrating. I mean it seems to run fine…but the engine seems to be moving side to side more…..

1982CorvetteDude

I wanted to give you guys a idea on my whole set-up so you can better help me:

Engine:

Stock 1982 Corvette Crossfire Engine, cast iron heads
No modifications to engine
Tested good on compression, new stock oil pump and stock water pump

Ignition:

Stock remanufactured HEI distributor, AC Delco Wires, Bosch Platinum 2 plugs, New coil, cap, and rotor. All ignition components are new.

Double checked TDC and firing order of wires….everything correct. Base timing set at 6* BTDC and actual timing at idle is approx 17* BTDC

Transmission:

Rebuilt 700r4 w/ overdrive
Has shift kit and new TC w/ a slight stall
Also using a 4000 pulse speed sensor in transmission
http://cgi.ebay.com/ebaymotors/ws/eB...m=220095546113

Engine Control Unit:

Remanufactured ECM 1227730, custom harness and custom chip
http://cgi.ebay.com/ebaymotors/ws/eB...tem=8071872892
1990 – 1992 Speed density set-ups
Chip is written for a Stock 1990 – 1992 5.7 Camaro TPI w/cast iron heads


Sensors:

All sensors are brand new
Map, IAC, Oxygen, TPS, VSS, IAT, CTS, and Knock sensors
New relays for fuel pump and fan
http://tpiparts.net/inc/sdetail/357

Fuel Delivery:

Brand new stock TPI in-tank pump
New crossfire fuel filter
Stock 22lb injectors, flow tested and checked w/new o-rings
Fuel regulator, used, stock and looked fine




TPI unit:

Stock 1986 TPI unit removed from a camaro
Has cold start delete using the plug and cap on fuel rail
Stock 48mm throttle body, throttle plates nice and tight
Brand new gaskets
New K & N filter on throttle body

Emissions:

No emissions – EGR taken care of on the chip
Has EGR block-off plate
No fuel canister purge, removed from chip. Throttle body has vacuum cap on that hook-up.
No pvc valve, spot in manifold is capped off
Have hose ruuning from passenger valve cover to throttle body vacuum.

Charging system:

Rebuilt stock starter (brand new)
Rebuilt stock alternator (brand new)
Brand new battery
All new belts and hoses

Cooling:

Stock water pump
Dual spal electric fans
Aluminum radiator

I think that’s everything…

Now Symptoms:

1. Slight miss at idle
2. Seems to be running lean, fumes burning eyes like tear gas.
3. Chugging at cruising speed, goes away upon acceleration, comes back after letting off gas
4. Several plugs have white film on electrodes…sign of lean condition
5. Vacuum check shows vacuum at 19 inches at idle slightly fluctuates between 19 and 18….kind of like a heartbeat.
6. Vacuum at 2000 rpm holds steady at 25 or so inches…no movement.
I didn’t seem to have any of these issues until I installed the TPI system, it ran decent with a carburetor. Hopefully that’s everything……I've got a cable coming in so I can hook my laptop up to the ecm and get a better idea on whats going on..

Thanks for the help!