youngrodder

I have a 95 Vette LT1 motor in my 1948 Chevy truck. I have a Howell engine harness and reprogrammed CPU. Non emission set up. My motor starts up but idles rough. It sounds like an old Harley.





I have confirmed that my fuel presser is in spec.

Here is what I think are the possible causes.
1 - The motor sat for 7 years. I am thinking that I need to have the injectors cleaned.
2 - I am running open headers. insufficient back pressure.
3 - Opti

Looking for feedback.

Thanks in advance
Marc

Ravant

Honestly, I'm going to have to say a combination of 1 and 2. Try cleaning the injectors first, see what happens. If you've still got a nasty idle problem, then see what you can do about increasing backpressure a bit. I don't mean go to the extreme and put 1.5" piping after the headers, but to be honest, I've never seen a problem with an LT1 in the past while running open headers, so cleaning the injectors should clear everything up.

Can you pull data off the ECU? An air-fuel ratio would be perfect in order to find out what exactly's going on in those combustion chambers.

yamaryder6

i have a very similar project. same exact motor,open hooker headers right now, just got the fuel cell and lines all plumbed up and i also gutted all emissions. i am almost ready to start it, and i would be very interested in how your progress goes and what you did compared to what i did, thanks o ya its in an 83 chev sb 2wd slammed (same concept as yours)

youngrodder

I need to run a scan. I will either need to purchase a scanning tool or try to rent one. I am not sure if that provides air to fuel ratios. My goal is to get it running smooooth before I go to paint.

I am running my own exhaust (2.5" stainless with 50 series Flowmaster mufflers with an x-member) and I just about have everything I need. After I get the injectors cleaned it wouldn't take much to hook up the exhaust.

I should also mention that when I felt the headers, I noticed some of the tubes were much hotter then the others, which also lead me to believe that it is an injector problem. I did run all new taylor plug wires and new plugs.

Thanks
Marc

youngrodder

Anything you would like to ask, just shoot me an e-mail. I had a few minor set backs when trying to fire mine, but nothing major.

Your project sounds cool.

Good luck.
Marc

LawrenceF

Swap your injectors around and see if the cool pipes move with them. Are you running a MAF? If not you'll need to tune it a little to get your idle right. Even with the MAF mine needed work, and without the MAF it was rough.

Sweet truck too.

youngrodder

I am running a MAF sensor. I have a noid light so I will test that each injector is getting a signal to fire. Then I will run the motor and unhook each injector one by one to see which ones are working. I was also told that sometimes lightly tapping on the injector will sometimes free them up.

After doing all of that I should have a better idea if it is an injector problem.

Thanks for the reply.

LawrenceF

Push the injector plug gently with your finger as it's running, you can feel it firing.

daniel6718

iTrader: (36)

scan it and the o2 are prolly gone crazy with the open headers...

youngrodder

Good suggestion. I will try it.

Thanks
Marc

mullenh

iTrader: (1)

to test the injectors you do not need to swap them. you can unplug them one at a time. when you get to one that does not change the idle you may have found a problem. normally i would doubt that it is an injecor issue but you did say 7 years. if you can borrow another maf. getting the motor scanned at a shop of course is the best choice of all. very nice truck.

the last car that had a rough idle that I looked at was not throwing any codes at all and it was a broken valve spring (2002 6.0 ltr. with 200k)

youngrodder

I did confirm that each injector is receiving a signal to fire with the use of my noid light. I then tried to unhook one at a time and it seems to me that only about three injectors are working. The motor is a low mile (15K) motor.

I also tried tapping on the injectors while the motor was running and it seemed to get a little smoother.

I must admit I am confused by the MAF comment. When you say MAF do you mean the sensor or the duck work? This was brought up before and I was not sure what they meant. Please explain.

Thanks for the feedback
Marc

mullenh

iTrader: (1)

the MAF sensor would be between the throttle body and air intake. I do not even see one in your engine photo!? look up LT1 MAF sensor (google it) and you will see a photo, your computer should be hooked up to it.

youngrodder

I see. My Howell harness does not require the use of one (I think). My harness is a non emission harness. I think that is why I don't have a MAF plug in on my harness?

Does that sound right?

edcmat-l1

iTrader: (10)

Looks like hes setup to run SD. Typical of the conversions.
You are probably on to it, OP, if you tapped on the injectors and it sounded smoother. You probably freed one up. Go out and get a mechanics stethoscope. You should be able to hear a pretty good click, click, click, from them with your stethoscope. If you dont hear that, then they're stuck. Tap on them with a brass punch and a hammer. You can wack em pretty good. I been doing that for 15 years. I think I'm the one that came up with the idea. LOL
Now, even if you hear a click, it doesnt mean the injectors good. It could be moving the pintle, and just be clogged. If thats the case, you need to pull them and get them cleaned.
When you go out to buy your stethoscope, get an infrared temp gun too. They are the best thing since rubber tires!! LOL
You can use it to find dead cylinders, just point and shoot the header tubes.
Also good for finding draggin brakes, hot and cold spots in the rad, countless uses.

edcmat-l1

iTrader: (10)

Yes, you probably are setup to run speed density. Which is typical of conversions.

youngrodder

I know that I need a temp gun. I used the feel method. You know touch the header to realize what is hot and what is not. Ha ha. I did notice that some of the tubes were much cooler then others. I don't have a radiator yet so I don't let the motor run too long.

I don't think that I am tapping on then injector hard enough. I was just slightly tapping on them.

I think that I am gaining on it.

Thanks for all of your help.

youngrodder

Update!!

It was the injectors that were the culprit. I purchased a used set off eBay and it fixed my rough idle. It sounds and runs sooooo much smoother.

Thanks for everyones feedback.
Marc