I got my new fuel injectors today for the delta 88 (remanufactured, still vacuum sealed in bags, $60 shipped for all 6). So, I proceeded to take the fuel rail off, and popped the injectors out....well, I noticed that fuel injector tips were LOADED with carbon, as is the intake manifold....so I'll need to take that off and clean it out. Perhaps this was the cause of my rough idle problems?

*I also got a 200 amp alternator....a little while ago*

TOC Admin
Brando 8)

Hi Brando, hello everyone,


Not supposed to happen, I'm wondering how it got there. Are they all the same?

Regards, Norm

i remember us talkin about how carbon could get into the fuel injectors and intake, but i dont really remember how it happens. i know it does somethin with the intake valve. may not seat well but there is somethin else that sucks the carbon in there it just on the tip of my brain... I know it happens in racing alot. If i can find the instructor that told me about this i will get back with u all. -Intimidator68

Do you run ethanol up in Michigan? That can cause carbon fouling of the injectors. I saw that a lot when I lived in Idaho.

C.J.

Well...I did some reasearch, and we do use ethanol. 10% ethanol, 90% gasoline.

As far as intimidator's comment, are you talking about the valve stem seals? I read about them wearing out, so I figured I'd replace those while I have it apart (both intake and exhaust).

88coupe, yes, they are all the same.

TOC Admin
Brando

brando - rough idle has plagued us all with that bloody 86-88 3.8L since I can remember... I just came to the conclusion that this was what the enhancements of the 3800 version of the motor gave. Balance shaft to smooth the idle, and overall a better motor.

But anyways, let me know how your injector replacement goes, and if it improves the idle any. I'd never turn down a chance to improve the idle of my own car!!!

no...you see, my idle was smooth.....it's much worse than what it used to be. So....basically I am doing a top end rebuild now. I got the intake off, now I am thinking I am going to take the heads off too, get those cleaned up too. I stripped the intake of all its accessories (labeled everything and where it goes, of course ), now what should I do with it? Might have to check the machine shop out at school....

TOC Admin
Brando

If you have carbon build up, heat it with a torch and burn the carbon out of it. IDK if that would warp it or not, so you may need to have it milled too...

Andrew

as long as the temp of the torch rench doesnt exceed around 1100 degrees he shoudl be fine for the valves. the neck area of the valve is where the carbon builds up. the intake seal would be leaking to cause a buildup of carbon on the stem. this buildup can cause turbulance in the airflow, which reduces volumetric efficiency (breathing ability) and decreases power.

Hi Brando, All,


Good time to do a complete head job. Part of it, is to check the valve guides for wear and replace as necessary. Worn guides are harder to seal.

Shop at school can answer all your questions. The labor cost is low, but the quality of the work is only as good as the instructor.

Head surfacing (if needed) is part of the job. In your case, milling is out of the question. It's only done at your request, and is normally charged by how much material you want removed.

Regards, Norm

Hi andrewk, All,


Burn carbon?

Rotary wire brush on your favorite drill motor, die grinder, or grinding wheel will work fine.


Hard to warp a head with a torch, but if a head needed to be surfaced, the shop would clean the carbon off first.

Regards, Norm

EDITED: for spelling, punctuationity, and clarity. 8)

Hi Intimidator68, All,


Interesting number. Why did you use it?


This is normal buildup, and partially explains the injector problem, but not how carbon gets into the manifold.


Not enough difference to measure.

Regards, Norm

the stuff i wrote down came directly out of a book from my school. the temp says in some kinds of valves they can go up to 1300 or 1400 degrees. this is just the temperature certain parts of the valve (especially exhaust) have during engine operation. the air turbulence has a drawing of a valve that is pretty much a carbon ball. atleast 1/4 inch of carbon buildup on that valve. a vehicle would have trouble running at all if it had that much. ill see if i can figure out how carbon got into the manifold for ya. -Intimidator68

This could be a possibility of the carbon buildup in manifold. Heat risers sometimes become stuck. Most often they stick in the open position, but sometimes they stick closed. This causes carbon buildup and possible cracking of the intake manifold floor. A stuck vavle can sometimes be loosended up by tapping on its shaft with a hammer. Special graphite heat riser lubricant can be applied to the shaft. To work properly, a vacuum operated heat riser should have sufficient vacuum present at idle. If the valve is not working and there is at least 10'/hg vacuum present, there is a problem with the diaphragm, linkage, or butterfly valve. Hope this helps you. -Intimidator68

Heat riser? I don't see mention of that anywhere in my service manuals, or on the napa auto parts site...

TOC Admin
Brando