dhirocz

iTrader: (2)

Been having a hell of a time to get this '89 running right. LTR vortec 383 car running a t56.

when idling:
O2's showing under .100 V consistantly.
consistantly idles high, regardless of how many times I reset the IAC. Idle counts at 50-65 at 'idle' which is about 1500 RPM.
TPS at .60 V.
frequently detonates off idle under load.
usually find it with 20-40 knock counts but no knock retard.
Integrator bounces between 128 and 135.
mild idle surge, on the occasions I can get it to idle down (immediately following an IAC reset).
4*BTDC with 22-25* advance.

when driving:
O2's show normal. Perhaps a touch high.
sensitive to detonation. Sometimes it doesnt, sometimes it does alot.
Cannot go over 50% throttle or it detonates. However, in N it revs fine.

I've tried every trick in the book to get it to run fine. The tune is the only thing I can think of that would be posing a problem. Now I didn't tune it nor am I here to bash anyone, I'm just at a point where I need to know if I'm chasing something mechanical or the tune.

I just finished tightening the shims in my distributor and I replaced my ICM and pickup coil. Starts and runs easier otherwise. I recently drilled open my idle air bypass, which solved alot of idle issues (surge, stall) due to the lack of the passage, but now it idles high as hell regardless of how many times I reset it (I drilled to a standard 3/32" size in the factory location).

I tried backing off initial timing from 8* BTDC to make it less detonation sensitive (no), using the FPR to richen it up somewhat to make it less sensitive (nope), changing to colder plugs (nada), etc....

This is a different car, running the factory ECM than the one in my sig. Any input?

Mr Froman

I would start with the 02 sensor. Seems sluggish and dead.

Orr89RocZ

iTrader: (20)

reset TPS to .54 volts. Drilling out the idle passage may have caused too much of an air leak and thus the high idle speed. May need to replace that throttlebody assembly/plenum or whatever you drilled open to shrink that air bleed.

Idle surging likey a fuel issue and timing.

Sensitivity to detonation can be a combination to a few things. Fuel, timing, compression, spark plug heat range...etc. What compression are you running and how hot of a spark plug do you have?

Get a wideband sensor to double check your o2 air fuel ratios...Can use narrowband to tune somewhat but its best to have an idea of whats going on with a more accurate wideband sensor.

Verify you have no vacuum leaks, that can cause lean conditions and high idle too.

dhirocz

iTrader: (2)

I didn't drill the passage any more than that of the same size and location as my other TPI and LT1 throttle bodies. I doubt that could be the root cause, but with such a small hole, I could plug it if I needed to. I've also tried the TPS to .54, .50, and .60. No luck.

compression is 10.5:1 with 93 octane. Never had a problem before with a street grind cam at that compression. I figure with the compression that high it would be more sensitive to spark advance though. Plugs are one heat range colder than stock.

Get a wideband sensor to double check your o2 air fuel ratios...Can use narrowband to tune somewhat but its best to have an idea of whats going on with a more accurate wideband sensor.

Verify you have no vacuum leaks, that can cause lean conditions and high idle too.[/QUOTE]

I've been all over the engine to verify there are no vacuum leaks. If there are any leaks, they are hiding rather well because I can't find them.

I've considered the injectors being part of the problem, but unless they are plugged, I dont see how they could be a major contributor. They aren't that old and resistance is within spec on all within .1 ohms.

rgarcia63

Do you have headers if so you'll need to switch to a heated O2 sensor.

Orr89RocZ

iTrader: (20)

10.5 on iron heads? Thats pretty high and would definately be very sensitive on 93 octane if the cam is rather small. Sounds like it would be since you are using vortec heads and a TPI. Vortecs like less timing as it is due to the combustion chamber design, so with you running high compression, its only gonna want less timing. I'd run 2 heat ranges colder at that compression if the cam is under 230 deg duration. Thats a start.

Once you verify fueling is spot on, then work the timing but sounds like its not quite optimal on fueling yet.

dhirocz

iTrader: (2)

I can go another step colder on plugs. I can also shorten the gap from .060" to .035 to cut off some of the heat as well.

Cam is rather small, a 218/224 duration. At least he quench is tight at .038"

dhirocz

iTrader: (2)

SLP shorties. I'm considering switching to a heated O2 and seeing what that does.

dhirocz

iTrader: (2)

Found what looks to be a problem. My scan tool says fourth gear is always engaged. Now correct me if im wrong, but doesn't the ecm add timing and lean out the fuel mixture if it thinks 4th gear is engaged due to the tcc for lean cruise( which I no longer have since its a six speed)?

Orr89RocZ

iTrader: (20)

I dont know of anything that would add or subtract fuel or timing depending on the gear.... I dont understand what issue being in 4th gear would cause? Unless you had highway mode enabled...it could be possible.

You have a bin based on a Manual trans L98 vette? I'd use either that or a 305 TPI 5 speed bin and retune it for the 383.

dhirocz

iTrader: (2)

it's an '89 305 TPI 5 speed bin. I disconnected the 4th gear switch wire from the connector at the back of the ECM and plugged it back in. No change. I dont think there's a way to manipulate the PROM into thinking 4th is always engaged is there?

My understanding is the computer adds timing when it thinks it's in 4th gear and the TCC is locked up for lean cruise. Problem is there's no A/T!

Orr89RocZ

iTrader: (20)

I havent seen anything like that other than highway mode which has to be enabled to work. I dont think you'd have that if you are using a 5 speed bin. I never played with highway mode before but if theres a feature for 4th gear TCC lockup then thats not your issue since you have no TCC in the bin file or in the car

burnout88

One thing I have seen with Vortec head cars is if the bypass line is not run from the intake to the water pump you can get alot of detenation/pinging. Without the bypass you will get some really crazy temp swings on the cylinder heads.

Did you run external bypass from the intake manifold to the water pump?