my 85 vette is hard starting in am....then fine all day...I changed the IAC and that eliminated all starting problems except in am...s florida...not really cold....I put a fuel pressure guage on...38 # with key on....now....how long should that pressure hold..???? I 'm really leaning on it being the cold start injector....would that throw a code???

 

Your pressure is good at 38#. It should hold for about 8-12 hours dropping about 2+ pounds per hour or so.

 

38 is ok? Shouldn't it be like in the low to mid 40s?

Also when the OP changed the IAC, were the passages and the TB cleaned with the IAC housing removed? Any leaks? Was it reset to whatever the spec was, assuming it is 100% stock? Or is it modified?

 

cleaned TB when I changed the IAC....also reset it...idle had been dropping but new IAC cure it. read several places that 34 + was good for fuel pressure....also read several places that you can't get cold start injectors....

 

just went out and checked pressure....drops to 0 in 15 minutes.....bad diaphragm in fuel pump??? or injector??

 

Could be bad Fuel Pressure Regulator or Bad Injectors.

I would pull the air hose going to the FPR from the manifold and pressurize the line. If it has gas coming out, you have a bad FPR.

To isolate, crimp off the return line in the fuel tank area, re-pressurize and see if it drops. If it drops, you have a bad FPR.

Either case, I would say to also get a set of injectors or at least have them cleaned and tested while you are there. I don't think much of the stock Multec injectors.

 

Did you take the IAC housing off and clean the passages around them and the housing too?

How did you reset it? Assuming it is stock, there is a procedure around, I set it using IAC counts but either way works for a STOCK engine.

Not sure about 34, mine is at 43.

What cold start injectors? IIRC, there is only one. I would take it off and send it out for cleaning and testing since you are having cold start issues. Also test and clean the injectors if you don't want to dump them for the newer Bosch III injectos. Stock Multecs are crap, IMO

 

the car has 117,000 on it....probably could use a new set...you say bosch III are better? I thought that if FPR was bad...car wouldn't start hot..mine starts and runs sweet after that initail start...could I have missed something cleaning the TB?

 

It could have used a better set with 1 mile on it. I don't see any problems with Bosch III. http://fuelinjectorconnection.com/sh...php?groupid=72

If the FPR is bad, it will drop pressure quickly like you are saying assuming the injectors are not also leaking. If you smell gas in the hose, it is leaking. If you pressurize it and fuel comes out of that hose, it is leaking.

As to running sweet, you cannot be sure from the butt dyno that it is running at optimum. It could be compensating.

If the FPR is being done, why not do the injectors while you are there?

As to the Throttle Body, did you remove the IAC housing and clean it and the passages from the housing into the TB also?

 

keep thinking I didn't do good enough cleaning the tb...is that something that could be causing my problem...? I have a hyperchip in it....will a code reader still work???

 

••••• TESTING FOR LOSS OF FUEL PRESSURE

... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator

To reach the lines to pinch off for the above test, you have to remove the fuel cover door and then the rubber dam around the filler neck. Your lines are under the rubber dam.

For the 1985 with the ignition On: 34-39 psi, at idle 24-36 psi.

 

thank you so much for the information....i'm sending for a factory service manual so I can do this right. MY feeling is to replace the fuel pump/injectors/and fpr since I have to get in there anyway. 117.000 miles ...anything else I should replace if I go in there??don't want to waste money but I want the car to run good and last...I''m retiring soon and feeling to old to be under a c4 in the summer in s florida

 

Cold start injector that is bad will not throw a code.

I would run the tests first and see what you come up with before spending the money. With the age of the car and the miles on the engine, it is about time for new injectors. Injectors will require more time than the fuel pump which is easy to replace. Check with Jon at FIC for injectors. The 85 uses a 24 pound injector, Jon will confirm this.

If you have time and tools, you might do a little gasket matching on the plenum and runners while you have them off. if you end up replacing the injectors. You will not see huge HP gains, but it all adds up. While you are down that far, pull #7 and #8 plugs and check for oil fouling. This happens many times with bad intake manifold gaskets.

**Be sure to use anti-seize on any bolt that goes into aluminum. Be aware that there are different size bolts on the runners. Mark each as you remove them. There are also two (I believe) bolts on the inside of the runners under the plenum that bolt the runners to the intake.

 

well, something is throwing a code at the cold start...service light stays on....restarting it ends the service light. been like that for awhile. I'm going to invest in a scanner although I don't know if it will read codes with the hyper chip in....called them, they don't know either. wouldn't be happy if I have to put that damn chip back in...way too old to be upside down that long....

 

I'd ditch the hyperJUNK and see what comes on.

 

i'm getting the feeling the the experts don;t like the hyper chip....th engine definately runs cooler with it...couldn't tell performance wise....thought it was pretty hot before the new chip...

 

if you think buying that chip was bad....I can confess to worse....I bought (and installed) a vortex rammer air system....piece of crap...can't last long, in the way of my aux fan...saved the stock system thank God....

 

I made the mistake of buying the Hyperchip years ago. We all do foolish things when were are first learning. That was before the Forum.

Do you know how to pull codes using the paper clip method? You might have a problem with getting a scanner to read the 85. It was the only year that GM used the 870 chip.

 

i've read that auto xray works with an 85....wondering if I can pull the codes with the paper clip method with the hyperchip still in?....I'll remove the battery cable to clear the codes and try it after the 1st cold start...should be only 1 code....after 1.2. A little off the track but, I watched a video of a guy removing the rail to change injectors...he used a t handled tool with a long shaft to remove quite a few screws....know what that was??and what size???? good thing i'm ordering a service manual...

 

I bought the Auto-Xray years ago when I first got the 85. The codes it showed didn't match the codes that were pulled by my mechanic. I called the tech line for the reader only to be told that it did not support the 85 Corvette! That was money thrown away.

Suggest you use the paper clip. Open up a paper clip so it forms a "U". Remove the plastic cover on the ALCL which is located under the dash about where your right knee would be. Now insert the paper clip in the top two slots to the very far right. These are A & B reading right to left. Now turn the key to the ON position (do not start the car). Your check engine light should flash.....once...then twice. This is code 12 which indicate the computer is communicating the the diagnostics mode. The code 12 will flash a total of three (3) times. Any additional codes will be flashed three times each before moving on to the next code. After all the codes have flashed then code 12 will flash again three times. Take a piece of paper and pen with you so you can write the codes that are displayed.

You should be able to pull any codes regardless of the chip that is currently installed.

You will have to use a Torx socket to remove the bolts from the runners to the plenum. Then there are Torx bolts that hold the runners to the intake. Removing the plenum and the runners will give you full access to the fuel rail. I believe that the rail screws are also Torx. Be aware that you should relieve the fuel pressure at the rail. Also take off the gas cap to relieve any pressure in the tank. Next be aware that you have to un-bolt the fuel lines from the rail. Fuel will leak out quickly even if you have released the pressure. Have a couple of rubber caps that you can push over the fuel lines to seal off the leaks. Suggest that you also replace the "O" rings on the fuel rail at the same time injectors are changed.