A few days ago my 89 vette was experiencing a fuel starvation issue, and would die. I assumed the fuel pump so I replaced that, unfortunately it still is acting up the same.

In addition I found this (see photos) unplugged! I can't figure out what it is, does or why its unscrewed? ?

Thanks,
Brian

 

Ops, photos....I need to figure out how to load them up!

 

You can post pictures directly if you have a paid membership.

Otherwise you have to upload them somewhere else and put in a link here. Click the "Go Advanced" button or surround the link with [I M G] link [/I M G] (without the spaces between the letters IMG).

 

Thanks Cliff, that explains a lot!

So, Here is the issue I am STILL having & what I have done to try to fix it:

Problem:
Running rough & dying, wont stay running unless it feather the gas, but runs rough. Rpm surges from 300 to 1200. No codes thrown at all.

Replaced (stock type):
1) fuel pump and sock, no effect.
2) fuel filter, no effect
3) new coil, no effect
4) new Ignition Module, no effect

less than 4k miles ago complete tune up with plugs, wires, cap & rotor.

At this point I am completely baffled as to what the heck is going on or what to look at next. Is there anyway to diagnose this or do I just have to keep throwing parts at it?

 

99.99% of the time surging idle is caused by a vacuum leak.

The easiest way to fix this is to block off the vacuum sources one by one until the problem goes away. The sources are:

There are two vacuum sources on the rear of the plenum, passenger side. One goes to the A.I.R. valves and the fuel pressure regulator. The other goes to the vacuum check valve near the distributor, where it splits and goes to HVAC system in the cabin and to the cruise control.

There is one vacuum source on the rear driver's side of the plenum that goes to the vacuum brake booster. A cracked booster case or ruptured diaphragm can cause a vacuum leak.

On the bottom of the throttle body is a vacuum source that goes to the EGR solenoid (and from there to the EGR valve -- but that only operates when cruising). On later cars it also goes to the vapor canister.

There is one more source on the driver's side of the intake manifold that goes to the PCV valve. On earlier C4s it also goes to the vapor canister.

If the EGR valve is frozen in the open position it will cause a vacuum leak.

Another possibility (though in my opinion it is rare) is for the throttle valve bores to be worn and sucking in air.

If you're running very rich it could be caused by a ruptured fuel pressure regulator diaphragm, which basically pumps raw fuel into the plenum.

Once all this is sorted out, you should do a minimum idle adjustment. Here's how to do that:

http://www.batee.com/corvette/dcrg/r...scuss_sim5.htm

Getting pictures added to this thread will help a lot. There are lots of very knowledgeable guys here that can identify your problem area.

 

So, finally have a fuel pressure guage that works. At key on, but engine not running, I had 40 psi. Running at idle I had 37-38psi. When she started to slow her idle like she was about to die the pressure would increase to about 40psi. I would then give it a blurp of the right peddle and she would catch herself and back to idle and around 38psi. Oh, and the vacuum lines are still connected when I tested the pressure.

Ok, So after researching the fuel pressure, there seems to be a lot of differing ideas. So, is my pressure ok? Can I or should I drive with the guage attached & taped to the windshield to see what its doing while driving?

I havent checked for vacuum leaks but will try this soon.

Thanks!

 

Well, if I am checking my injectors correctly for an Ohm reading here is what I got: 13.9, 13.3, 12.7, 16.3, 12.9, 16.3, 15.3, 12.6. So do I have injectors going bad? I read 16.0 as the cut off to stay above on this reading.

however, while I was on the injector near #1 cyl, I saw a little hose maybe 3mm wide outside diameter, broken. It was kind of a hard plastic vs rubber & it was broke where two of these little hoses come together to one. After they came together, then the hose snaked down to the area in front of the drivers side tire. When I traced the other end of the broken connection in the other direction,( part of it snapped off in my hand) and it went to the bottom of the intake plentum at the front of it drivers side.

So am I correct that I may have a vacuum leak from this hose? Sounds like its related to the EGR system. Could this be a cause for its rough running? As for a replacement hose, do I get the same kind and if so from where?

Finally, it looks like quite a bit of work replacing injectors, what else should I be doing as protective maintence or as a good upgrade if I am having to do injectors and taking off the intake, etc...???
THANKS!

 

I also pulled off each injector's electrical connection one at a time and ran the engine after each was disconnected. My thought was that if it was a "bank fire" system and if one shorted then they may all be shorting. Unfortunately it didnt seem to make a difference at all.

Am I correct in thinking it has a bank fire fuel injection system instead of each injector firing individually?

 

Time for new injectors I suspect with readings like that
Did you test hot as well as cold?

Intake stays in place you only have to remove the plenum and runners to access the fuel rails

 

Correct

If one is shorted the computer will shut that whole bank down

 

Would it be correct to assume that if one of the injectors is shorting out and perhaps stuck open, that if I disconnect that sensor then the rest will start firing normally again?

I thought I had read this somewhere.

Also, with the EGR hose broken comming off the bottom of the intake, would that be affecting the running? With the little plastic hose needing replacement what can I use? It looks more like a hard plastic vs rubber hose, so is it best to get an exact replacement and if so where?

Thanks!

 

The broken hose you describe is for the PCV valve and vapor canister purge.

All 8 injectors fire at the same time. The "bank fire" thing is a myth, as I proved here:

http://forums.corvetteforum.com/c4-t...-debunked.html

Your injector resistance readings are all over the place, which indicates that you have multiple bad injectors. My recommendation is to call Jon at FIC ASAP:

http://www.fuelinjectorclinic.com/

If anybody needs convincing that Jon is "The Man" when it comes to fuel injectors, see this thread:

http://forums.corvetteforum.com/c4-t...questions.html

 

Cliff,

I contacted the link you posted and there was no Jon?

 

The problem has been found & fixed. Unfortunately no one got it right!!!