Over revving 350 ramjet. Help?

[Eugene]

I am eugene. I own a 1970 fj40 with a 350 ramjet, with a mefi4 system. I am having a problem with over revving. When it warms up and in open loop mode it revs up from 1000 idle rpm to 2000 to 3000 rpm once it goes to open loop mode. When it does this my breaks cannot keep up with the power. It is generally when the fans kick it. After it went to a shop I found the connector on the o2 sensor partially melted on the tail pipe. Also noticed that when I pump the breaks the rpms increase. Any ideas?

[dontlifttoshift]

When it warms up it should go to closed loop, if it is stuck in open loop, fix that first. Did you fix the O2 connector yet?

Check all of your grounds, including the ones for the fans, including the main harness grounds, including body, frame, and engine straps or cables.

Check for vacuum leaks. Check and see if your booster is leaking vacuum, sounds like it is.

[TomsResto]

Everything Donny said sounds like valid approach to troubleshoot ... only thing I can offer in addition is that owning a RamJet 350 myself I have found there aren't a ton of shops out there that are familiar with them here in the midwest so after some calling around I found the following shops and made some notes for my future reference that I'll share in case it helps you at all (now or in the future).

Supposedly Arizona Speed & Marine in Chandler, AZ collaborated with General Motors on the MEFI setups, with the intention this powerplant would be big in the marine industry. I spoke with a guy named Jim down there last year and he seemed very knowledgeable on the motor & ECU (albeit more from a marine application perspective). They'll take ECU controllers and re-program them for you for $400.

I also spoke with a guy named Bob at MEFIBURN in California who was knowledgeable on issues the ECU in general on the MEFI controllers. They offer to have you send in your ECU's (can't remember pricing he offered but think it was less than AZ Speed & Marine) and they'll flash upgrades to deal with various issues folks encounter ranging from hard starts to "phantom idles" to going into limp mode when warm. When I came across the phantom idle issue in other forums it was generally described as like a "hung idle" where you lift off the gas pedal approaching a stop light after holding steady throttle and it continues to pull at the RPM you were holding driving down the road. That doesn't sound like your issue though if it's surging to the point that brake pressure is at risk of not holding it back.

Hope you find the issue, let us know what you find out.

[andrewb70]

Sounds like you might be better off ditching the MEFI and getting something more user friendly, like the Holley HP EFI system. You can keep all your existing hardware, just get the Holley ECU and harness. You'll have a great EFI system and tons of support in the community and also various shops that are familiar with the system.

Andrew

[TomsResto]

Sounds like you might be better off ditching the MEFI and getting something more user friendly, like the Holley HP EFI system. You can keep all your existing hardware, just get the Holley ECU and harness. You'll have a great EFI system and tons of support in the community and also various shops that are familiar with the system.

Andrew

Interesting... I'm not currently having any issues with mine (was previously just calling around on a quest to find someone around that does know about these RamJet 350 crate motor setups in rod/custom applications) but I'll tuck your recommendation away for a potential future reference. Do you recall if anyone out on the forum has already did a build thread on their conversion from MEFI to Holley ECU on this crate?

[andrewb70]

Interesting... I'm not currently having any issues with mine (was previously just calling around on a quest to find someone around that does know about these RamJet 350 crate motor setups in rod/custom applications) but I'll tuck your recommendation away for a potential future reference. Do you recall if anyone out on the forum has already did a build thread on their conversion from MEFI to Holley ECU on this crate?

I have not seen any direct swaps, but it shouldn't be that hard. Holley does not have a direct replacement harness, but personally I would start with an unterminated harness and take it from there. Then again I am not afraid of engine wiring. As I recall, the RamJet used a standard 3 bolt LS1 throttle body and presumably it uses a pretty standard electronic distributor. I believe the MEFI is batch fire, so I would go a step further and get a dual synch distributor and make the system fully sequential. The HP includes a wideband and has self learning for the fuel map. Your RamJet will run way better and you won't be a slave to some remote "tuner."



Andrew