Need advice on aftermarket computer

[73z-6sp]

It looks like an aftermarket computer may be my only choice if I am to get my RamJet running correctly.



How much can I expect to pay for a good system? The guy that will be tuning it is recommending big stuff 3 though he says he has done other systems. How much can I expect to pay for the computer? How about the cost of tuning? What is a normal amount. I dont have a problem paying someone to do the job but I want it done right for the right price.

I had my car at AS&M in July of last year. It cost me over a grand to get it dyno tuned. It took me a few more months time before I was able to drive the car on the road and when I did it ran awful and has a bad hesitation off idle. Some of you have read about their software and computer for MEFI4. Attached is a copy of their page for this computer system. Notice the second sentence. How ironic that I paid to have that problem fixed by the company who says their software can fix that problem! Go figure. Im tired of learning things the hard and expensive way so I am hoping you guys can lead me in the right direction.

The shop I took it to last week says they are sure it is a programming issue and not a mechanical or sensor problem. They said it will cost me three hours at $70/hr to diagnose it using the existing sytem. If it is in fact the programming, then the only option I have is to find a way to change the parameters which I cannot do with my current set-up. Another ironic thing is that AS&M tried to sell me the computer and software so I could change the settings but I didnt want to spend that much at the time because I figured I didnt know how to tune it anyway so let them do it right the first time and I wouldnt have to worry about it.

Anyway, what do you guys recommend? If I were to buy something like Big Stuff 3 would I be able to learn how to change the parameters and eliminate my dead spot? Or is it best left to someone who has done this stuff. (Im thinking the latter) And if I do end up needing a computer system, what do you recommend?

Thanks,

Aaron

[ProdigyCustoms]

A complete XFI set up with a dual sync distributor for sequental operation, with a start up program writen for your motor will run about $2700 through us. Expect to pay $300 to $500 for dyno tuning

[DeltaT]

I have nowhere near the experience of Frank, but I've work on & tuned 8 cars now with aftermarket EFI (mostly the Holley 950) and 6 of them, including mine, had fundamental problems OTHER THAN the EFI that needed fixing before I could actually tune. 5 of them, again including mine, had at least one wiring or ground problem (I had one wire wrong out of like 100, ouch!), and 3 had several wiring problems. Others had fuel issues. One had the spark plug wires in the wrong positions!

My point is that you shouldn't give up yet on your Ramjet and its proven controller. Consider getting Jeff Hartman's excellent book "Tuning and Modifying Engine Managment Systems" for like $20 from Amazon. He has an entire chapter on troubleshooting sensors, and his 'EFI101" chapter takes you through from startup to a great tune in understandable steps. In most cases you need an inexpensive digital VOM, which can be found for under $50 new.

I hope it works out for you.

As an alternative, check in at Chevytalk.com on the EFI forum, and see what Doug_F says about the Holley 950 box running the Ramjet wiring harness with simple mods. You can get the holley 950 for under $800, or around $1000 with the wiring harness and sensors.

HTH,

Jim

[73z-6sp]

Thanks guys.

FWIW...I have gone through the manual that comes with the RJ and have done the tests for each of the sensors. None of them check out bad according to the tests. I have checked the grouds, separated all three on different locations, added more ground straps. I have 7 grounding straps connecting the engine, frame and body. My fuel pressure is good and steady while idling and during driving. Im not saying that there isnt a chance but I'll be damned if I can find it. And its been several months that I have been pulling my hair trying to figure it out. Im surprised I have any left!

So is it worth it to pay the guy 3 hours to diagnose the problem? I'll be out 200 dollars if our suspicions are correct. But I guess thats a lot less than the 3000 Frank said.


I will look into that book you mentioned. I need to learn more about this. I should have gone with a used LS2 and aftermarket computer to begin with! I would have been in it for less than I am now. Hindsight...go figure.

[ProdigyCustoms]

For the record, I agree with Delta. If that thing is stock, it should run off the original ECM. I know Mike Norris had one in his shop a few weeks ago. Not sure what was wrong but it was running rough, acting weird, and while he could not communicate with the ECM to tune, he was able to straighten it out.

I would not think about a aftermarket FI for it unless you modify the heck out of it. And even then there is probably someone that can work with the system it comes with.

[73z-6sp]

The engine is stock. The programming isnt because Arizona Speed and Marine did a dyno tune on it in July of last year. I havent been able to figure it out on my own and I cannot keep going like this. Too much time has been wasted on it. I dont want to buy a new computer but I cant leave it like it is either. So its either find someone who can fix it, or convert to a carb. At 3000 dollars, the carb is sounding better all the time. But that sucks because I have put so much effort into the FI and it makes the car different rather than the same ol same ol. Its frustrating to say the least.

[PTAddict]

MSD now sells a programmable version of the MEFI 4, and they claim they have an off-the-shelf version calibrated for the RJ:

http://msdfuelinjection.com/mefi4.html

This setup was actually marketed before by UMI racing, and seems to be quite well proven in a number of other applications.

No idea on price, although it's almost sure to be significantly less than BigStuff or FAST.

I would also think that you could just order a replacement, pre-programmed ECU - I'd bet they're not too expensive, they're made in large volumes because they're used on all the marine EFI motors as well as the crate engines.

[PTAddict]

Also, here are a couple of links to Sallee Chevrolet's information on the RJ, and their RJ bulletin board, which might get you some troubleshooting tips.

You might try posting there or calling Sallee and see what they recommend ...

http://www.sallee-chevrolet.com/Disc...tml?1176814672

http://gilbertautoparts.com/ChevySma...m_Jet_350.html

Two things I'd check on: is your fuel pressure right, and is it correctly vacuum referenced? Does your TPS accurately track the throttle?

[73z-6sp]

Sallee hates me.

Fuel pressure is right and doesnt drop during driving at all. I dont know how to see if TPS is accurately tracking. Can you explain?

[DeltaT]

Sallee hates me.

They hate you so much they sold the dealership and are now Gilbert Chevrolet!

Like PTaddict said, if your fuel regulator is manifold referenced (it probably is), you should be able to hook up a gauge and watch the pressure while it idles. Then remove the vacuum line from the regulator and block it off with your finger. Unhooked it should read ~6-8psi higher than with the vacuum attached.

There are different types of TPS. Most are linear and the voltage or resistance increases in direct proportion to the amount of travel of the TPS. Some however have a curved scale where the voltage or resistance rises faster at the end of the travel than it does during the middle of the travel. Some of these variations are even available in the same style and look package. It is worth checking to see if you have the right one, and plotting the output for say, each mm of movement. Again the book discusses.

What does AS&M say about your problems?

Jim

[73z-6sp]

They hate you so much they sold the dealership and are now Gilbert Chevrolet!

I gotta clarify...that was a poor attempt at a joke. I dont know that they hate me but they got tired of me posting on their website. I was one of a few who werent happy with the RJ and was vocal about it too much I guess. I will check the fuel pressure vacuum tomorrow and see what that reveals.

[PTAddict]

I'm not an expert on TPS testing, but if you do some searching on posts in EFI forums you should easily turn up a testing procedure. Basically, you're looking to get a certain range of TPS signal voltages at idle and WOT, but more importantly you want to make sure that the TPS voltage varies continuously as you open the throttle. For instance, if the TPS fits sloppily on the end of the throttle shaft, the ECU won't get signalled on small throttle movements, and thus won't know to shoot proper acceleration enrichment. That would definitely cause a stumble ...

The thing I was wondering about on fuel pressure is whether the pressure is correctly vacuum referenced - I believe the fuel pressure on these motors is regulated constant relative to manifold pressure, rather than atmospheric pressure, although I could be wrong ... If the fuel pressure is regulated relative to manifold vacuum, a conventional fuel pressure gauge will actually show pressure fluctuation as the throttle is opened/closed. If the vacuum referencing doesn't happen, the engine will probably idle because the closed loop correction will compensate, but then on tip-in, when the pressure should rise, it wouldn't rise and you'd go lean.

I mention these two things because any tech would have to check these right off as part of a diagnosis, and you can probably do them yourself.

Good luck, and for what it's worth I'm sure this can be worked out and it won't cost $3K unless you want it to (i.e. unless you really want a BS3 or FAST controller, which are very nice if you're into it - I have one of each on my cars).