Please help!!! 85 vette hard start problem
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
Muffin has a point - Start at the Beginning.
The base timing Has to be set someplace close to right - right meaning what the Chip is expecting it to be. There is an "offset" value for the distributor baseline timing advance that is set in the PROM - the distributor should match that number. Or be pretty darn close to it. If you need to have the distributor someplace different then you Also need to burn another chip so that they Match. It matters, mostly if you want the thing to start and idle correctly.
The min idle setting also Has to be pretty close to "right", or the thing will Never idle right. Run through That proceedure, meaning set the idle stop adjustment then reset the TPS calibration. Has to be done, otherwise you are fighting a losing battle. Yes, I know, the thing has to be able to Run at idle before you can set the idle stop. This is a problem.
50 Psi with 26lb injectors is Way too rich for a mild tune like this. Do the math - the original '85 used 24lb (yes - that is correct) injectors at 40 psi (approximately). That's the ballpark you need to be in - say within about 10% of that, at the Furthest away.
Finally - you really need to have a scan tool on this with it Running. You need to see what the sensor readings are - mainly the MAF and O2 numbers. That and see what the ECM is commanding for IAC position, pulse width and etc. Otherwise you have no real idea what the ECM is fighting.
One other thought - sounds to Me like you have a big time vacuum leak someplace. Just a guess. It's easy to do that with the TPI setup - hard to assemble it and Not have a leak. Hooking up a vacuum gage would be interesting..
The base timing Has to be set someplace close to right - right meaning what the Chip is expecting it to be. There is an "offset" value for the distributor baseline timing advance that is set in the PROM - the distributor should match that number. Or be pretty darn close to it. If you need to have the distributor someplace different then you Also need to burn another chip so that they Match. It matters, mostly if you want the thing to start and idle correctly.
The min idle setting also Has to be pretty close to "right", or the thing will Never idle right. Run through That proceedure, meaning set the idle stop adjustment then reset the TPS calibration. Has to be done, otherwise you are fighting a losing battle. Yes, I know, the thing has to be able to Run at idle before you can set the idle stop. This is a problem.
50 Psi with 26lb injectors is Way too rich for a mild tune like this. Do the math - the original '85 used 24lb (yes - that is correct) injectors at 40 psi (approximately). That's the ballpark you need to be in - say within about 10% of that, at the Furthest away.
Finally - you really need to have a scan tool on this with it Running. You need to see what the sensor readings are - mainly the MAF and O2 numbers. That and see what the ECM is commanding for IAC position, pulse width and etc. Otherwise you have no real idea what the ECM is fighting.
One other thought - sounds to Me like you have a big time vacuum leak someplace. Just a guess. It's easy to do that with the TPI setup - hard to assemble it and Not have a leak. Hooking up a vacuum gage would be interesting..
Thread Starter
Intermediate
Joined: Aug 2006
Posts: 34
Likes: 0
From: Erie Pennsylvania
I should probaly clarify that when I said I drove 100mph home, I was was exaggerating and I was driving my Truck not the vette! I was in a hurry to get hame and try adjusting the timing! Which by the way, sort of helped but it is hard to just the right spot to place the dist.
Safety Car
Joined: Nov 2008
Posts: 3,717
Likes: 551
From: Seattle Washington
May I suggest you are swatting at flies with a baseball bat. You have made multiple changes to a car with little if any idea how they all fit together. Strongly suggest you go back to basics, read what Agent 86 said, pull codes for a direction. First you need to set timing and TPS by the book. All else being equal your installed injectors may not be the best but the car should run. Last, I can understand why the Techs don't want to touch this thing, it doesn't fit in any of their training and experience. Did you actually get it to 100 MPH?
You say You have all the left over Parts. Good. This means You can try them. Lets first make it Run and then make it Fast. If You can't get the Timeing right there isn't much point continueing on. The Tuner I had said that the 85 ECM is so primitive that the only way it will set a code is pretty much if something is disconected. The previous Owner who had my car wasn't afraid to Spend Money throwing Parts at it but never took the time to take it to a Tuner to make it run. He was willing to spend big bucks on fast and shiny looking parts but not waste any on tuning when there was nothing to show for it. The full Day I had the Car at a Tunner wasn't cheap but the car went from 50 Hp to 300 Hp and nothing looked any faster. This is the most common problem of do it yourself Hot Roding, I know cause I have done it myself.
