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Help! Rich cold start

keremarsan

Well-known member
Joined
Oct 21, 2006
Messages
55
Location
Istanbul / Turkey
Corvette
1988 Coupe Z52
Hi ,

Since some times, my car has rich cold start situation.

For the first 3-4 sec , the car cold starts perfectly with approx 900 -1000 RPM. Then RPM decrease to 800 and I can feel the engine not comfortable and smell the gas from exhaust pipe.

This situtation continues for 20-30 sec then suddenly ca begins to run normally, as the temp is low, RPM increase to 1000-1100 and after warm up, decrease normally to 600-700.


The problem begins some month ago with a strange noise of "friction"( I can hear this even the car is hot and run normally ) .

It is a well maintained 1988 corvette with 84.000 miles on it ( I have it since 2006 , since 62.000 org miles ) . Noise is present, there is no problem of oil presuure, no error code .

It is strange that the cold start rich problem begins with this "friction"noise that I can not find where is the source ( looked at air pump, try to here with stetoscope, noise seems to come under the car , but can't find the source. )

I made the iddle setting following the procedure , TPS at iddle is 0,54 V, spark plugs are new Bosch platinum ( I was having same problem with previous spark plugs ) , If I describe the strage frictionsound, it seems to come because the engine is not comfortable due to a ignition problem. But I have plenty of power any loss of power is present.

I have a second ECM with Hypertec street runner chip ( I have a 180 degre thermostat ) , I canged my ECM and same friction sound , cold start issue is always here.

I can hear and feel the "friction sound " even in decompression of the engine.

Fuel pressure is normal ( start and running ) , fuel injectors were changed las summer with 24 LBS accels and work great until now.

This strange "friction noise" and cold start rich issues make me very sad. I have a lot of expreience in mechanic but can not find the solution .

( I have already ordered new water pump, new air pump , air pump delete kit, BBK 52mm throttle body etc and try to change everything to find a solution ).

IACV also is new. ( but the original was better I think )

I have also a new Cold Start Swicth and think to change it, ( just under the air intake coupler ) but I have already eliminated the cold start injector.

My car has now a 1989 model year hypertech performance chip to help te cold start by using main injectors.

But even with the standart 1988 chip, I have the same problem.

Any additional information wil be helpfull

Thank you for your help

kerem
Turkey
 
My guess is with the replacement injectors...

I have seen different complaints with almost every replacement fuel injector...hard cold starts, rich starts, high idle, everything.

It seems that the small change in injector resistence has some effect on the duration of the fuel inj pulse. It's my guess that the ECM has to "hunt" for the correct bandwidth because it is not getting the feedback from other sensors that it expects to see with its cal-pak programs. I cannot think of what else it could be. I know that my personal research for the hard cold start issue with Bosch-III injectors has eliminated the temp sensors, fuel pressure, IAC, TPS and everything else since its either been replaced or adjusted. The ONLY thing different is the injectors themselves.

What to do? I have no idea. I have learned the most effective start up sequence and just live with it. Not much else I can do since being stock with stock componants and a stock tune is out of the question...just not possible anymore.
 
Thank you ,

For the first 5 month after the replacement if the injectors, I had any problem. This problem begins with the strange noise that I can not fix the source but I will check the resistance of injectors to be sure that is not the reason of my problems...

Thank you for your help


I have seen different complaints with almost every replacement fuel injector...hard cold starts, rich starts, high idle, everything.

It seems that the small change in injector resistence has some effect on the duration of the fuel inj pulse. It's my guess that the ECM has to "hunt" for the correct bandwidth because it is not getting the feedback from other sensors that it expects to see with its cal-pak programs. I cannot think of what else it could be. I know that my personal research for the hard cold start issue with Bosch-III injectors has eliminated the temp sensors, fuel pressure, IAC, TPS and everything else since its either been replaced or adjusted. The ONLY thing different is the injectors themselves.

What to do? I have no idea. I have learned the most effective start up sequence and just live with it. Not much else I can do since being stock with stock componants and a stock tune is out of the question...just not possible anymore.[/QUOTE]
 
Problem Found !

Problem Found !

Hi !
I want to share this experience with you , my both exhaust muffler were blocked ! I use a light to see what happens ( I suspect the mufflers ) and see that a part inside the left muffler blocks the exhaust gas and on the right muffler there is a lot of like "artificial hair" inside.

Sure, these were done by somebody.

That proves that for the first 3-4 seconds of cold start , car starts great then begins to decrease the RPM due to blocked exhaust and this explain also the strange sound ( some resonnace occures on all the way the exhaust due to blockage ) :thumb

:beer:beer:beer




Thank you ,

For the first 5 month after the replacement if the injectors, I had any problem. This problem begins with the strange noise that I can not fix the source but I will check the resistance of injectors to be sure that is not the reason of my problems...

Thank you for your help


I have seen different complaints with almost every replacement fuel injector...hard cold starts, rich starts, high idle, everything.

It seems that the small change in injector resistence has some effect on the duration of the fuel inj pulse. It's my guess that the ECM has to "hunt" for the correct bandwidth because it is not getting the feedback from other sensors that it expects to see with its cal-pak programs. I cannot think of what else it could be. I know that my personal research for the hard cold start issue with Bosch-III injectors has eliminated the temp sensors, fuel pressure, IAC, TPS and everything else since its either been replaced or adjusted. The ONLY thing different is the injectors themselves.

What to do? I have no idea. I have learned the most effective start up sequence and just live with it. Not much else I can do since being stock with stock componants and a stock tune is out of the question...just not possible anymore.
[/QUOTE]
 

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