Hey all, today I became a part of the C4 family by buying a nice '91 6 speed car. I'm very excited as I have big plans for the car for the future, however there are some issues that need to be addressed first and I'd like to get some advice from the veterans here.

The car has 76k on it and is in good shape for its age, and it has a pretty extensively detailed service history which I can reference. The car definitely has a parasitic battery drain issue which I should be able to track down myself.

My main concern is that the car is running a little rough. It is idling high at around 1100rpm, even after warming up. It's hard to explain exactly how it's running rough so I'll post a video. The car does not throw any codes.

The previous owner installed a hypertech chip on the car. Could a bad chip be the source of the car running rough? The car does not have any other performance mods besides the chip. He actually included another hypertech chip (which is attached to a hypertech branded board of sorts), but not the stock chip apparently. I want to return the car to stock to really assess the health of the engine. Where can a stock chip be sourced?

It smells like it's running rich. The car doesnt smoke anywhere or overheat as far as I can tell, and has no fluid leaks. There is however a blatant exhaust leak under the car, as well as a knocking noise from underneath. The knocking is not consistent (with rpm) and does not sound internal to the engine, so my first guess is that it's a loose exhaust issue. I should be able to confirm one way or the other in the next few days. I know the flywheel can be a source of knocking noise so I hope it's not that.

My main goal is to return the car to stock and get a real thorough account of the health of all its parts/systems before I really start working on it. I plan on building the car to compete in time trails, so I want to get a good idea of what the car needs before I move forward. This site has been a tremendous source of info for me thus far, so hopefully some of you can help me out! Any other good general advice for owning and racing a C4 is very welcome as well, thanks.

 

Possibly a vacuum leak....causing the high idle. And ANY exhaust leak that might be at the engine is NOT GOOD.

Rattling noise can be a bad/broken catalytic converter....just guessing...it may not be and something loose.

AS for a computer chip....maybe call Gordon Killebrew and ask him.

Hooking up a scanner to your car when it is running will be VERY VALUABLE. Trying to 'pin-point' a problem without ti is a time consuming endeavor...and something I would NEVER try to do.

DUB

 

DUB has some good advice. I would try some Corvette recyclers for an OEM chip.

 

Thanks for the advice! You're right, buying a scan gauge is a good investment I've put off for too long. I guess I underestimated the data you can get from these old ecu's.

I think I've already found the culprit, though. I wasnt looking closely enough before, but the injector on cylinder 8 has a completely broken wire on it! It looks like a mouse chewed through it and started to chew on some other wires in the area. I'm glad I know where to start but it makes me concerned for wires around the rest of the car.

The wire is separated at where it connects to the injector, so I dont think I could easily solder it or anything. I do plan on either porting the stock intake components or going with a miniram setup in the near future, so I would need to upgrade the injectors soon anyways. Would it be a good move to just buy upgraded injectors now so I can get the motor running healthy and be set for the future? I would be hesitant to just replace the one injector for now...unless I wouldnt be able to use the same upgraded injectors on both the stock TPI and a future miniram setup. Thoughts?

I also plan on ditching the stock ecu and going with a Megasquirt III setup also in the near future. I just want to make sure the engine is running healthy on the stock computer before going forward with that install, just so it will be easier to trouble shoot if I have issues with the MSIII install. Make sense?

 

Knowing that you are changing the set-up in the near future....it is somewhat pointless in trying to get this one running perfectly. Get it to the best you can and checking the OBVIOUS 'things'...such as compression, crankcase pressure, oil pressure, etc.

You can perform an injector balance test....which is in the Factory Service Manual. the tool I use is made by OTC other than the fuel pressure gauge.

Getting a connector for your injector is not a big deal. I believe Standard Motor Products has them...I saw it in the catalog I just got...and I also got one form O'Reillys . And I know I could get a good used one so the wire colors are correct..due to the fact that I am very picky in that way.

Yes it makes sense to get it as good as you can so you are not working otu problems with a new system. But with the new system you may find that some issue swill pop up and need to be addressed. All I know that my time is very valuable...which is why I know I would stop if some issues are still present and are dealing with parts that I am going to replace with the new set-up.

DUB

 

I see where you're coming from, this is all great advice. I think we have the same mindset as I'm not looking to get the stock setup perfectly, but rather just running well so I can sort out what it needs before I really dig into it. And of course a main objective is to avoid buying parts or doing a job twice, hence why I'm trying to plan as best I can.

A compression or leak down test was definitely going to be my next step after sorting out the injector/fuel issue.

It's good to know that I can replace the injector connector separately. However my concern is that the fuel system has been serviced twice in the past, which included replacing the injectors. I don't know if they took the time to replace all the associated gaskets and o-rings for the fuel system. It's not leaking now, but I can't help but be a little paranoid with the risks associated with shortcuts taken in this area.

With that said I want to tackle the whole system at once since I want to be safe and will need to upgrade parts soon anyways. I'll also be able to replace some of the intake components gaskets while I'm at it.

From research it seems that the Bosch III injectors are a popular option. it seems that people don't have an issue running these on the stock computer. I'll probably install an AFPR for good measure as well. What I don't know is if these will work with an upgraded fuel rail and miniram setup, but I'll do some more research there. Any opinions?

After the fuel system is finished and tested, I'll tackle the ignition components and see what is needed there. Sorry if it sounds like I'm thinking out loud here, I just want to make sure I'm on the right track! Thanks for your input DUB

 

I'd remove the Hypercrap chip before I did anything else. See how it runs after that and then possibly perform some tune-up type stuff (plugs, cap, rotor, fuel filter, etc.).

 

The main thing here is getting your 'mind-set' on track.

I can not give you any option in regards to your fuel system. Not enough pieces of the 'Jeopardy puzzle' have been turned over for me to know the answer to that. Size of the throttle body if being changed, fuel pressure requirements, cam shaft profile...and on and on.

DUB

 

To be fair, I'm obviously not asking you to solve a 'Jeopardy puzzle' of my fuel system here. I asked pretty specific questions regarding the injectors alone, not my whole fuel system. for example, notice how I made no mention of the fuel pump? That's because I'm putting a fuel cell in the car eventually so it would be pointless to talk about that right now. That goes for the million other things around the car. I'm obviously not asking you to build my car for me.

Yes I am thinking out loud a bit here, but the point of the thread was mainly for some of the veterans here to share some info or tips in general and regarding to the specific questions I had. I appreciate your input thus far but to be honest you sound a little full of yourself.

 

NO...I am NOT full of my self...but you are entitled to your opinion.

And when I wrote...'getting your mind-set right'. I was referring to the improvements you plan to make in the future and invest your time and money into parts that will work for them. I know things can change...and often times they do. Obviously you took that comment I wrote NOT in the way it was intended. It is your money and time ..and you are free to do with it however you like.

BUT...I work on cars that are getting modified...and I KNOW what can happen if the 'plan' changes in 'mid-stream'.

TRUST ME...I am NOT wanting to build YOUR CAR. BUT...NOT knowing all of your plans...it was hard to comment on if the Bosch III injectors were/are the best choice. because if I wrote .."Yeah buy them and put them in"...and they did not work...then I get BLASTED for giving bad advice. I am F'd if I do...and I am F'd if I don't.

All I was trying to do was help. Thanks for thinking that I am 'full of myself....even when I spend time HELPING others on the Forum after a day of working on Corvettes. I see I missed the 'mark' on this post.

BEST OF LUCK...hopefully you can get the answers you need from others. I am sure that they are ready to help you out.

DUB

 

A bad injector, wire, miss etc can cause the dual mass flywheel to make some noise once sorted out it should quiet down
Hypertech chip is good to turn the fan on earlier doesnt do much for performance. Doubt it went bad. When you do all your mods you can get a custom tune and sell the Hypertech off.

Ck your throttle body to make sure the bushings arent worn and the butterflies arent hanging open

 

Listen, I'm not trying to start drama here. You've offered me some good input so far which has been useful and which I've thanked you for.

What I didn't want to do was lay out every bleeding detail of the build I have planned. You're absolutely right about plans changing. Mine has changed several times which is why I can't share every little detail as I'm still working them out. I thought that mentioning the planned intake mods was enough to get a ballpark idea about what injector options I had.

I also thought that it'd be obvious that I wouldn't just blindly follow your advice. I have plenty experience working on and modifying cars as well, and I'm an ME by trade. However I don't like to pretend I know everything, hence why I'm posting here.

This is a place for people to share knowledge and opinions, a "forum" if you will. Don't worry so much about being f'd if you say one thing or the other, I doubt any rational person would personally hold you responsible for an opinion. Not me at least.

 

Thanks, that's great info about the flywheel and TB. After doing more research I came to the same conclusion about the hypertech chip, I doubt it's causing any issues. I actually have a second one that came with the car so I could try that as well if I still have issues after I repair the injector connector. Also good to know that I can sell em if needed.

Here's a debatable topic for y'all since we're talking about repairing an injector connector: do you solder or crimp sensor wires in the engine bay? There doesn't seem to be a consensus on the interwebs, there's the camp that thinks the more reliable mechanical connection of a crimp is necessary, and the other camp that prefers soldering due to the added resistance of a crimp that can skew the signal of an injector or sensor. What's been people's experience here?

 

Wondered about that myself.
Electrical +me=fires every time.

 

Haha yeah I don't have the best track record there either. I'm going with soldering since I want to err on the side of caution since injectors are do resistance sensitive. My technique on the other hand...I'm definitely going to be practicing beforehand hahaha.

 

Stock injectors, IMO are basically junk so I'd toss them for the Bosch III stock size. As to the high RPM, I'd want to be sure it is really high per the ECM via a scanner before I trust the tach. Those can be off. I would like to see what the fuel pressure is and if it can maintain constant pressure under load. Tape the gauge to the windshield and WOT the thing down an empty road.

If your idle is rough, first thing I would do is clean the TB. Remove TB, remove IAC housing. Clean all passages. Fresh gaskets and install. Call up a couple of chip burning people and see if they can send you a stock flash.

 

http://www.ebay.com/itm/DELCO-16193416-EPROM-ASSEMBLY-1991-91-CORVETTE-CODE-8992ARZR-0277AXFK-3417BFXB-/281293835833?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1991%7CModel%3ACorvette&hash=item417e6b4e39&vxp=mtr

 

you didn't miss the mark...you missed the whole building...this guy's sounds intelligent yet can't take good advice....if you're full of it, i'd like to be too....

 

Yep, it seems like going with the bosch's will work right now and give me head room for power later (24's). Good to know about the stock tach. Definitely going to do fuel pressure, compression test, etc once I repair the injector connector lead (and MAP connector lead, that one is chewed up too). If the compression test is good and I dont need to do a leakdown test or touch the bottom end, then I'm going to refresh the intake/fuel/ignition/cooling components. I'm probably going to run the car stock for a while before either porting or going with a miniram. The rest of the car will get lots of attention as well.

Before I started looking I guess I just assumed that an oem chip would be cheap and easy to find. Thanks for the link on that, but for now i'm going to stick with the hypertech if it's not causing any issues.

The car will gradually start evolving into a full on track car, so after all that I'm going to delete all the unnecessary stuff a/c, egr, etc. Then I'll probably go all in and do the MSIII install. Fun stuff coming!

 

WINNER WINNER...chicken dinner.

YEP...MAP circuit damaged= PROBLEM. AND the injector issue as we all know... does not help either. Another piece of the puzzle.

ALL I can say is I hope your compression test is to your expectations.

AND...to clarify this..so you can understand my point of view. Because I an understand your point of view.

SERIOUSLY...I can not count the number of times when I give suggestions/advice on an issue when the forum member did not give all the information needed. So trying to help them...I replied to what information I was given and then they come back adding more pieces to the Jeopardy puzzle...which makes my suggestions/advice null and void due to taking the problem in a completely different direction. I 'felt' this in this post....so that is why I responded the way I did. WHY would I comment any more when the video was never posted so we all could hear it like you wrote. Why respond any more when a compression test had yet to be performed and could show that you have a bad cylinder which would make this entire post about an injector choice be futile. From your initial post you added more information that made previous advice and suggestions worthless. Now can you see my point of view. Being educated...I am sure you can. But yet you write that "I am full of myself".

It this post is no different than you be presented with 'something' that requires your expertise. You make determination on what you were given...then the next day more is given to you that changes the entire scope of where you are heading and how the outcome is entirely different. Putting your heart into what you do...I am sure it bothers you...just the same way it bothers me. I was just trying to help you and give you advice on what information I was given. Just like in your profession...ASSUMPTIONS are the MOTHER of all F'ups.

You wanted reply from a 'veteran' which I clearly am. I did my best.

Because ONLY speaking from experience...I have had the chance to do a compression test when diagnosing a problem that could be associated with loss of compression...and I thought that it was something else. So I spent the time doing what I thought. Only to finally perform a compression test and have a major problem. Then realize that the time I wasted doing 'other things' was a waste of my time and I could not ethically charge my customer.

Using or employing what I suggest it up to you. But the suggestions/advice do have merit...at least at that time in the post where the information given made them have merit. My comments come from experience and I would much better help you save time and aggravation. Instead of reading that you are struggling.

NO DRAMA here. I have no problem in wishing you the best. SERIOUSLY.

DUB