Chevy 350 computer troubles

[trevor kent]

Hello, so I have a 79' with a chevy 350 ramjet motor in it and it runs fine but very rich. On occasion it back fires and will stall out shortly after a back fire. let it sit for a minute and she fires back up again, thoughts? I need to get into this computer or have someone get into it but I know nothing about it. Is there a place to find the year of make on the motor as that will help id the computer and the codes it throws up. Is there a way to bypass the computer, I'm thinking no. Does anyone have any ideas as to what kind of shop would look at the computer and reprogram it or id the codes. I asked Speedway motors and they said take it to any GM dealer and they could work on it does this sound right? Someone also suggested a hot rod shop as those motors are frequently installed as upgrades, any thoughts at all to lead me down a path would be greatly appreciated.

thanks

Trevor

 

[reddingcruiser]

Call Howell EFI. They are fuel injection pros. There are others like Howell, but I've done a fair amount of business with them and always been satisfied. I actually just started installing their TBI harness in my 40 - excellent quality.

 

[RAYJON]

Ramjet uses the Marine computer. Should have a standard obd2 connector and anyone with a code reader can plug it in. My Guess is the o2 or map sensor went bad, check the map sensor it has a hose off the back of the intake to a small black box maybe the hose came off the intake. Ramjet is speed density, so it uses the air pressure in the intake for fueling compensation. Real simple system.. Look at the marine stuff for codes.. Good luck

 

[RAYJON]

One more thought the street rod guys run that motor a lot, do some searches on what they are doing when it runs rich, could be something simple. If you find someone with the right software and a wide band o2 a custom tune might be a good idea.

 

[trevor kent]

Thanks guys for the replies. My mechanic called Howell and got a mixed response and is supposed to call them back. I will start calling some of the hot rod shops around and ask if they know anything or could put it on the computer. The motor purrs but you can smell the fuel at the exhaust and this stalling issue makes me leery to drive it.

 

[RAYJON]

read a little your local Chevy dealer can plug in and reflash the ecm. Might be worth the hour labor to see what's in Gm's computer. If your local dealer is a jerk find another one..

 

[Downey]

Bad 02 sensor would have engine running lean or rich (no fuel mixture control), but then you'd get a check engine light with a bad sensor???

 

[chevurai]

Could be a leak in the exhaust manifold, or pipe upstream of the O2 sensor. It doesn't take much of a leak to cause the engine to run rich. Air sucked in will also cause the backfire.

 

[jim land]

your computer is an MEFI 3 or 4 , do you have an engine light ,if yes its you can use a small jumper or paper clip to identify code if your light is on

 

[trevor kent]

You Guys are the best! I'm an ok mechanic but electrical and these computers leave me apprehensive, so I appreciate any and all guidance.I will start calling on Monday to see if I can get someone to plug the computer in for me. I will keep posting updates but would appreciate anymore input from you guys. Just one more tidbit is that this is a chevy vortec engine. I never even played with computers for motors and I guess that is what is throwing me, How many different codes can there be for these motors in a TLC anyway? My buddy hooked his computer up and 4 codes came up but we didn't know what they were for as no Idea what the year of the motor is. It is my understanding that the engine can be tuned via the computer? A little lesson into how these computers are used interpreted and info applied would be helpful. Last thing is in the glove compartment where the computer resides there is a small light bulb that is part of the computer wiring and it is on constantly, not a glove box light.
As you can see I'm a little over the barrel with this truck. Help!

Thanks

 

[RAYJON]

Ok the codes you should be able to search for try google, the check engine light indicates something wrong, it's probably running in limp mode and that's why the rich condition.


there should have been a diagnostic manual with the motor, that will have the codes., if you didn't do the install I would go thru the manual below and double check what was done, trust me it's easier than tuning a Holley and a point distributor.

Once you double check the install. Figure out the codes and then check each one. Could be something simple as a bad ground wire.. The computer these use is real simple by today's standards should be able to solve it with some basic diagnosis.


it's basically a 98 Chevy truck motor with a cool injection unit and a better camshaft



https://www.chevrolet.com/content/d.../02_pdfs/ramjet-350-crate-engine-12499120.pdf

 

[trevor kent]

Thanks Rayjon. My mechanic is saying it's a 90's motor and puts it on his computer but doesn't know what the codes mean. I'm assuming limp mode in reference to the computer is that there is an issue with the motor and the codes will tell me where the issue is, sorry to be so basic. I'll print the chevy data tonight at work and look it over. I'll also go to youtube and watch some videos on using these computers. Once I get this computer thing sorted out this won't be so intimidating. Any thoughts on these systems the happy homeowner can buy online to diagnose the computers, I see them for sale between $ 100.00 to $ 200.00 dollar range and is this something worth investing in?

thanks boys

 

[sadam_husain]

its usually more likely to be a sensor or wiring problem than a computer, I wouldn't think an o2 sensor problem would make it as rich as you have described in the first post but its definitely one of the things on your list to check, a couple of other potential things are fuel pressure regulator and temp sensor if the ECM cant see the engine temp it can keep the fuel enricher tables active

 

[lcwizard]

@sadam_husain has a good start point. The gm fuel pressure regulators were prone to fail. I'm not certain on the Ramjet but if your
pressure regulator is like a lot of the post TBI regulators it will have a vacuum hose running to it. Unplug the vacuum hose and crank the motor.
With a complete failure it will shoot fuel out the vacuum port. If it is just in the beginnings of failure you'll see rich situations and slower leakage especially on startups. You may even smell fuel. If it is the regulator make sure and do an oil change after repair. It will have been sucking fuel into the oil.
Temp sensors can fail bad enough to run rich all the time although it's common they work the opposite at cold starts, not enrichening the mix
on a cold morning, basically a choke