Thread: 502 ramjet

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I would like to know if anybody else having problems with the fuel injection on the 502 Ramjet? The first series MEFI-3 was installed on the eary ones like mine. It wont idle and is serching up and down and runs extremely fat. I talked to GM PERFORMANCE and they said send the computor in for re-calibration. They told me I was out of warranty even though it has 218 miles on it, so I sent it in. Still ran the same! So I parked the car untill I could get some answers. Now I found out that the new 502 Ramjet has a new and improved MEFI-4 and that there is a kit to upgrade from MEFI-3 to 4. Nobody at GM told me this as I found this by reading the new GM PERFORMANCE PARTS BOOK It lists for 811 bucks and GM reminded me that I was still out of warranty. So now that I have gone this far why stop now! Well I purchaced the kit and installed it, a new wire harness with 02 sensor and new computor and it idles better but still searches and runs rich. Im not very happy about it and about to throw a carb on it. The car is a 70 Nova SS 502 RJ 400 Turbo ,3000 Stall, GearVendor overdrive, and a strange Dana 60 rear end NovanutWayne

If it was me, I think I would go back to the basics. You have reprogramed 1 computer, and then replaced it and the harness. Although it's not impossible for that to still be the problem, I think for the time being I would rule it out.

Don't know if you've done this yet, but I would look for things like a faulty sensor, connection, wiring problem to include grounds and proper voltages. I would also not ruile out something as simple as an intake manifold leak.

The old harness and computor, MEFI-3 only read air coming in and the new harness and computor MEFI-4 reads air coming and going out, it has a 02 sensor. The computors have different part numbers and the harness are not the same. It sounds to me like the first series was a design problem and they tried to correct it with the new one. The moter was expensive and the original computor didnt work and the upgaded kit helped it idle some what better but it still serches,and standing behind the car running gags you. I have checked for vaccume leaks and are none.

May I suggest the possibility of take the car into a dyno shop and either you or the shop doing the tune on a laptop? I'd do that before canning the EFI system.

Originally posted by wayneboitz
The old harness and computor, MEFI-3 only read air coming in and the new harness and computor MEFI-4 reads air coming and going out, it has a 02 sensor. The computors have different part numbers and the harness are not the same. It sounds to me like the first series was a design problem and they tried to correct it with the new one. The moter was expensive and the original computor didnt work and the upgaded kit helped it idle some what better but it still serches,and standing behind the car running gags you. I have checked for vaccume leaks and are none.

if its doing about the same thing as it was doing to start with then it probably is the same thing, When the computer find something wrong, that's what it does. it searches until it finds the best setting, but if the problem is out of its range then it cant adj. to it. cant the system be checked for codes? sounds like a vac. leak or a bad sensor and the computer is trying to make up for it by making the motor run richer. have you hooked a vac. guage up to it. with computer motors when something is wrong with it, it dont sound or act like a conv. motor, because the comupter has changed the fuel and timing settings trying to fix the problem. id look hard for a problem with the motor or sensors

Originally posted by DennyW
Very possible a sensor is telling the computor it is to lean, which would drive it rich. But, you should get a code for that. Right Mike?

12489400 TOOL, DIAGNOSTIC TROUBLE CODE
every MEFI system that ive seen has a way to check for codes. this is what they say comes with the MWFI-3 kit. dont see anything on the MWFI-4. i know 2 people that has these systems on their cars in my brothers car club and they like them. come to think of it it sounds like the cold start senser could be out of range.

Well I think its time yo go see my GM buddy with his code reader and see what we come up with. It pulls good vaccume at idle,timing is on,and the fuel pressure is right. The fuel lines are 6AN for feed and return. Pretty cool site,thanks for the info and will keep you posted

It used to run about 210 which i didnt like so I pulled the T-stat, had a 195 in it,put a 180 back in and it runs at 195 now. Im not running the bypass hose from intake to water pump and maybe thats why it runs hotter than the stat??

Originally posted by wayneboitz
It used to run about 210 which i didnt like so I pulled the T-stat, had a 195 in it,put a 180 back in and it runs at 195 now. Im not running the bypass hose from intake to water pump and maybe thats why it runs hotter than the stat??

you need to check what t-stat they recommend if you run the motor to cold then the computer will think the choke is on and richen the motor up. the lower the t-stat # the richer the motor will run. on most late modal motors the fans. come on at 225 degrees and go off at 215. with a 195 t-stat. you cant run the motor at the temp. you like, it has to be the temp. the computer likes. that's the reason you need to check all of the sensers. I don't know where the temp sensor is but if the water is 195 at the sensor then its gonna run rich, be sure that you tell the mech. that's gonna check for codes that you have a 195 t-stat in the motor. thanks, mike

ps- I think for that motor to run like it should then the temp. will be about 200 to 210, and its nothing wrong with that as long as it stabilizes there.

Originally posted by DennyW
Absolutely Mike. They have them run a little on the rich side anyway. And by running it lower, he's even richer, and that wouldn't bring on the check engine light, it would just run cold. The coolant sensor over rides the oxygen sensor, cause before it goes to closed loop, that is the main sensor for control also.

yep, and with a 180 t-stat it wont ever go into closed loop. if the temp gauge is in the head and the computer temp sending sensor is in the intake then the water in the intake might not be 195 degrees, and the water temp. is the only way the computer has to know when the motor is warm. i had a mech. one time put a rebuilt motor in a late modal ford truck, and the only t-stat he had was a 180 degree one so he put that one in and we worked on that motor for a mo. trying to find out why it ran rich, until he told someone he had put a 180 t-stat in, so we put the right one in and that's all it needed. I wont forget that for a long time.

FYI, the MEFI3 does have O2 sensor feedback if the option is enabled. GM apparently went cheap on the original RamJets and didnt provide the feedback.....I think that they didnt provide incoming air temp sensor either. I am running a MEFI3 with feedback enabled and it works great......IF you keept the water temp at the right level. For us old guys, it goes against our background to put a hotter thermostat in! GM had problems with idle stabillity on the 3.....caused by their El Cheapo no-sensor approach.

You can get a scan tool at Rinda http://216.230.203.183/marine/mtspec.htm
for this controller.

Arizona Speed and Marine sells an upgrade to enable O2 on a MEFI3. They live at http://www.azspeed-marine.com/

Also, Scott Urshel is knowlegeable. He is also in Phoenix at
http://umiracing.com/

MEFI4 is a later version. It has some dual engine balance reporting that a 3 didint have.

MEFIs were originally marine computers so they dont have all the interlock junk that a normal ECU has. Regardless of altitude, temperature, or gas, mine runs great!!! I'll never run a carb again.

mike in tucson

http://216.230.203.183/RamJet/ramjet.htm

Ramjet scantool link.

This is a must have. Most dealers dont have one and although you cannot tune your ramjet with it you can see what the computer sees and more easily diagnose your problems. I struggled with mine until i realized the computer was not recording run time due to improper power source. It would start fresh everytime and now that its squared away the block learn has much more info from the o2 sensor etc. Its a different motor.

I did talk to a gm tech at the sema show and he said they are working on a faster isc so they dont hunt for idle as much. But as of sema they hadnt fixed that. Mine doesnt seem to hunt that much but you can hear it adjust as it returns to idle.

I wouldnt ever go back to a carb. I am considering a more user friendly ecm though. It drives me nuts that my MEFI4 has all those cabablities that I cannot take advantage of without sending my ecm out to be reprogrammed. I did find a guy who cracked a mefi3 system but he doesnt have a 4 to mess with.

I have the laptop scan tool that Rhinda makes. Its great you can even record with it. You can watch temps etc and see time at particular rpms. Lots of neat stuff. Lots of controlls that are switched off Thanks GM. I think you can track dowmn your problem much faster with this. Mine was obviuos but until i saw from the ecm i wasnt sure what it was. I had asked several experts but they all told me the way it was wired wouldnt matter but guess what they were wrong. I doubt if you have the same problem but with the tool your problem may be as simple as mine was. good luck

oh yeah mine has factory thermostat 195 and runs between 190-200. It may creep to 210 in heavy traffic but cools right back down after it gets moving. The thermostat is critical to the computer i would put the 195 back in it. You can watch the temps with the scan tool as well.

Newbie to this site, awesome by the way! I'm up from astrosafari.com where we amuse ourselves swapping smallblocks and 2 speed transfer cases into Astro's & Safari's.
I'm an oldtimer? (44) who ran a big block Nova among other vehicles) when I was in my late teens/early 20's. So much for intros
BADFISH, how about an update...

Here goes; I'm planning a ZZ502 swap into my Safari. I've been researching what's involved in this swap, and am very interested in the Ramjet. What I would like to know is if it is correct to assume that ALL Ramjet 502's being sold today from GM automatically come with the closed-loop mefi4 system? As much as I was terrified of computer controlled cars back in the early 80's, I'm now just as terrified of the prospect of running efi in open loop.
Also, anyone here ever swap a BB into a Safari/Astro before? I'm just curious as to what clearance issues were encountered, etc...
Thanx for putting up with newbie questions, and I will be searching the site for relevant posts (before anyone bites my head off, telling me to do so LOL)

EDIT!!! Sorry about the size of the pic. Won't happen again

Motor's ordered. MEFI4 version (I insisited he verify first). Prolly get it within the next month. I now know that a b-block fits, it's the a/c that gets a bit tricky. Also, 'cause my truck is an awd, the torsion bars and front diff will make for "interesting" exhaust routing LOL. Thank god the truck runs a front sub-frame. I'll definitely be removing this from the truck for most of the work

Still waiting for news, BADFISH


Petey

Hey, I have a 565 pump gas BBC in my 72 Ventura II with FAST f.i..I'm having a terrible time tuning my system. System was pricie. FAST does not seem to be much help. They told me to use the data log system on computer and I have. System bounces around and you can not tell what is causing the bounce. Car idles great and WOT is awesome but cruising around at 1500 3000 rpm sucks. the car surges. Map sensor is all over and so is everything else. The surging makes you think it's lean but changing fuel ration doesn't help. So don't feel like the Lone Ranger. Right now I have 400 turbo trannie problems. What can I expect it has 400 miles on it since I bought it. I't came from a pretty well know racing trans. builder. I also have a Gear-venders unit with an early olds 4:56 gear. Motor dynoed at 752 hp at 6200 rpm. Car is on www.pontiacventura.com 1972 page 6 3/4 ways down page. Boy could I tell you the problems I had putting it together. Thats another story