Ram Jet 350 Engine problems

If anyone reading this is experiencing similar problems with the Ram Jet, please let me know.

 

Sorry, but in an effort to reduce spam, you will have to type in the email address.

I have had the Ram Jet 350 engine installed now for about 4 years and have put over 20,000 miles on it.  My engine came with the original MEFI3 injection system. The only problems I have encountered with the engine are (1) it runs rich and (2) it will sometimes stall out after a long cruise. 

The stalling usually occurs after a long run on the interstate when you pull off and stop at the end of a ramp. Several people I have met through internet forums have also complained of this stalling problem.

The running rich problem also seems to be a common complaint. In an effort to lean out my old MEFI3 Ram Jet 350 I installed an adjustable fuel pressure regulator and an Innovate wide band air fuel meter. By reducing the fuel pressure I got it running about as lean as I dare to take it, but my cruising mileage only increased about 10%. The engine still seems to be running rich.

In March, 2006 I installed the GM MEFI4 upgrade kit (GM # 1249916).  This kit contains a new wiring harness, computer, O2 sensor and IAT (Inlet Air Temperature) sensor.  After installation the engine fired right up on the first try. I checked and set the base timing, drove it around the yard a few times and all seemed well. The next day I drove the car on a 200 mile trip and everything seemed fine till I got out on the highway. I was cruising along in high gear at about 1400 RPM and lifted off the gas. Well, it was like the car had cruise control (which it does not) or like the throttle was stuck open. Instead of slowing down, the engine seemed to maintain it's current RPM level. I took the car out of gear and the RPMs immediately went up to about 3000. Put the car back in gear, applied the brakes and pulled off the road to check under the hood. By now the engine was idling at about 800 RPM. Checked the throttle linkage and everything looks fine.

I continued on my trip and the engine behaved properly as I shifted up through the gears. I was shifting easily and letting the RPMs fall between shifts. I got up to speed (about 1400 RPM) and cruised along for a few miles, and when I was on a nice long flat stretch of road I took my foot off the gas. Again the engine RPMs did not come down. I took the car out of gear and the RPM's increased to about 2500-3000. This time I kept it out of gear and after about 10-15 seconds the RPM's started to fall and it finally reached idle speed and stayed there. This problem continued for the entire trip.

I borrowed a Rinda Technologies TechMate scan tool from a friend and hooked it to the Ram Jet so I could tell what the sensors were doing when the problem occurred.  Of course, the scan tool was for the MEFI3 system and I had to order a new firmware upgrade to get it to read the MEFI4 computer. 

The problem is that when your are cruising at relatively low rpms (1200-1400) and low engine vacuum (like when climbing a grade) the IAC valve is driven to it's limit and stays high for about 15-20 seconds even after the throttle is completely closed.  I replaced the IAC valve but that had no effect on the problem. I put the old MEFI3 system back on the engine and it ran fine, so I guess that ruled out bad sensors (except for the O2 and IAT which are not used on the MEFI3 system) or a vacuum leak. After comparing the sensor readings on the MEFI3 and MEFI4 systems, the one difference I noticed was that on the MEFI3 system the IAC valve would reach a maximum value of 150 and on the MEFI4 system the maximum value reached was 250.  When this problem occurs it usually takes about 15-20 seconds before the engine rpm starts to fall, but at least twice I  have had the problem persist long enough that I had to pull off the road and cut the engine off to cure the problem.

My car has a T56 6 speed transmission and a 3.08:1 rear axle ratio so when I am cruising at 70 mph in 6th gear I am only turning about 1400 rpm.  If I cruise in 5th gear (about 2000 rpm) the problem seldom occurs; however, if I cruise in 5th gear at 1400 rpm, the problem will still occur.  In fact I have experienced the problem in all gears at the lower rpm.

I contacted the dealer where I had purchased the upgrade kit and told him my problem.  He in turn contacted some engineers at GM and they sent me a new ECU to try but the replacement ECU still had the same problem. Since then the GM engineers have been able to reproduce the problem on one of their test vehicles using my old ECU and also with one of their ECUs.

I have posted the problem on several internet forums.   Here are the links.

http://www.sallee-chevrolet.com/Discus/messages/3418/6100.html?1152533430

http://www.chevytalk.org/fusionbb/showtopic.php?tid/127566/post/903852/hl//fromsearch/1/#903852

http://www.sallee-chevrolet.com/Discus/messages/3418/6616.html?1154829185

At the request of the GM engineers I replaced the adjustable fuel pressure regulator with the original Ram Jet regulator, but this made no difference.

July, 2006.

Since the Ram Jet ECU is protected and is not user  programmable, I have been experimenting with a mechanical fix for my Ram Jet "automatic cruise control" problem and I have made some progress. Based on the theory that the IAC valve was opening too far, I made a small plug that fits into the hole in which the IAC vale pintle normally seats. Basically this has the effect of moving the seating surface about 0.22 inches outward. I have tested this on a few trips and so far it seems to work (sort of). The computer is still driving the IAC valve wide open under certain conditions (low rpms and low engine vacuum) but now, when my problem occurs, instead of causing the engine to rev up to around 3000 rpm when I depress the clutch, the engine (so far) will reach a maximum idle of only 1250 rpm. Below is a picture and dimensioned drawing of the plug.

 

 

Before I installed my "fix" I had the engine hang up at high idle (about 3000 rpm) for over a minute on several occasions. On one occasion I had to pull over and shut the engine down to clear it. I have received emails from someone who has an automatic transmission behind his Ram Jet and he has experienced the exact same problem several times, almost running a stop sign on one occasion when the engine hung.

Based on some of the posts on the internet forums, and also the fact that the GM engineers can duplicate my problem, I am convinced that this is a programming problem that needs to be "fixed".

I have been in contact with several others who have experienced this "automatic cruise control" problem with brand new Ram Jet 350 engines with the MEFI4 injection system so the problem does not seem to be restricted to the "upgrade" kit.

If you have a Ram Jet 350 and want to see if you engine has "auto cruise control" try this - put you car in it's highest gear and cruise at 1200-1300 rpm.  Climb a small grade (about a 2%-4% grade should work) to place a slight load on the engine and maintain engine rpm for about 5-10 seconds.   Take you foot off the throttle and see if the rpm's drop or remain constant.

 

Here is my theory on this problem:

My MEFI3 system ran for over 20,000 miles without experiencing this "automatic cruise control" problem. My experience with the MEFI3 system was that is ran great but too rich. It also had a tendency to stall at low rpms, especially after cruising for long periods of time.

The Ram Jet was originally designed for marine use but these engines were being in street rods and other vehicles. Because of all the accessories that were now being added, plus the MEFI3's tendency to stall, the programming for the MEFI4 was changed in order to try to prevent stalling in the lower rpms.

Just a theory. Still hoping that GM will come through with a proper "fix".

 

July 20, 2006:

Called GM Customer Service and explained my problem.  Their suggestion was that I needed to take it to a GM dealer and let them look at the problem.  I asked the customer service representative if he thought that a local dealer would be able to fix the problem when the GM engineers could reproduce the problem on one of their vehicles but were not going to fix it.  The customer service representative asked if I had a case number and I again explained that, so far, I had only talked to the dealer from whom I had purchased the upgrade kit and did not have a case number.  So I asked how do I get a case number and the answer was, of course, you have to take it to a GM Dealer and let them look at it.

 

 

July 25, 2006:

I have been in contact with the dealer from which I purchased the original Ram Jet engine and here is his exact reply:

"Yes your complaint is not the first I've heard  with this problem.

It has always been worse with manual transmission cars.

The problem has to lie in the programming of the MEFI module.

There's really not a whole lot I can do for you.

I forwarded your e-mail to GM, lets see if I get a reply."

 

July 26, 2006:

Took the car to a Chevrolet dealer today.  On the way to the dealership the car was really acting up.  At one point I was cruising along, up and down some rolling hills, when the engine went deeply into “auto cruise” mode with the IAC stuck on 250.  I took my foot completely off the gas pedal and the car maintained 60-70 mph for over two miles.  Finally had to downshift in order get the IAC to start declining 

 The service manager and the Corvette technician at the dealership were very helpful, friendly, and understanding.  The technician called his contact at GM technical support and was told that they could not help since the engine was a "Performance Part".  The GM tech guy recommended that we call the "Diagnostic Hot Line" and they should be able to help.  This hot line is a non-GM related (I guess) commercial service that charges $3.25 per minute for talking to them.  I had my doubts about calling but decided to try it anyway.  After giving them all my personal information and a credit card number I was told that a technician would call me as soon as one was available. The technician called within a few minutes and I knew I was in trouble when he asked if my Ram Jet was a 350 or a 383.  After explaining my problem, he gave me some general injection possibilities like bad IAC, bad TPS, bad MAP sensor, etc., but had no solution, $16.25 wasted.

 My sole purpose in going to the dealership had been to generate a GM case number. The dealership technician said that since GM technical support could offer no assistance he could not give me a case number.   So, while we were still at the dealership, we called GM customer assistance and once again explained our problem.  The customer assistance lady wanted to know what year car it was, where we bought it, and if it was still under warranty – remember this as a 1962 Corvette. Then the customer assistance lady wanted to speak to the technician, and after only 20-30 minutes on the phone, we had a case number.   The customer assistance lady said that she would research our problem and call us back tomorrow.

July 27, 2006:

Well, it is 5:00 PM and no call from the GM customer assistance lady.  Will have to call her tomorrow.

 

July 28, 2006:

GM customer assistance lady will not be in until Monday.

July 31, 2006:

Called the GM customer assistance lady.  For some reason she has to get back in touch with the service manager at the dealership where I took the car.

 

August 2, 2006:

Finally got a call back from GM customer service lady.  She has been unsuccessful in contacting the service manager at the dealership but she will continue to try.

 

August 22, 2006:

Still no word from Customer Service

August 28, 2006:

Corvettes@Carlisle trip.  This was the first really long trip that we have driven the car with the MEFI4 system and my IAC plug "fix" installed. We drove the car a total of 1036 miles with about an hour of "city" driving and averaged 29.8 mpg so it looks like the O2 sensor must be working correctly.. 

While at the car show I stopped by the GM Performance Parts exhibit to see if they had any Ram Jet experts that I could talk to.  The fellow I talked to told me that the people manning the exhibit were not even GM employees but rather they were from a marketing group hired by GM.  Needless to say there was no useful information obtained.

October 27, 2006:

Finally received a call back from GM customer service.  After talking to the customer support lady and her supervisor, they have no suggestion on what to do since the part in question is a "Performance" product and they deal strictly with production cars.  Their only suggestion was to go back to the GM dealer from which I purchased the part.  So I guess this experience is like a lot of other things these days, no one wants to admit they made a mistake and you are just stuck with a faulty product.  I guess when someone with a Ram Jet engine in his car rear ends someone and the lawyers get involved, then perhaps GM will respond.  I have expended enough energy on this problem. If anyone reading this information has a better solution, please let me know.   

 

August, 2007:

I have been investigating the possibility of getting some tuning software that would work on the Ram Jet ECU.  There seems to be two primary sources for this software, MSD and Arizona Speed and Marine.  Both look like they might do the job, but they are both proprietary in the sense that they are “locked” to one controller, and the MSD software is also run protected with a block device.

I attended the big Corvette event at Carlisle PA this year and my wife and I were sitting with our car on the display field when this fellow  (Bob Radke) walks up and starts asking about my Ram Jet engine. He asks me if I was the person who had posted about the Ram Jet “cruise control” problem on several of the internet forums.   Well it turns out that Bob is a programmer for OBD Diagnostics, Inc. ( www.mefiburn.com ) and they sell scanning/tuning software for the Ram Jet and other MEFI equipped engines. Their software is not proprietary and will allow you to tune any of the MEFI controllers. The only problem is that the GM Ram Jet ECU is password protected and the only way for the user to tune it is to wipe out the original tune and load another one and then start tuning from there.  We also discussed some ways of cracking the Ram Jet password protection. 

 

November, 2007:

I purchased the OBD Diagnostics software which consists of three programs. 

 

1) MEFIBurn is their software that permits uploading/downloading  of  tunes to/from the MEFI controllers.  It does have a function for entering a password, but, of course, to download a program from a protected controller, you must first have the password.

 

2)  Tuner Pro.  This program allows the user to change any of the tuning parameters in the data file and save it.

 

3)  Scanner Pro.  This program allows the user to scan and data log engine parameters as the engine is running.

Both Tuner Pro and Scanner Pro are written by Mark Mansur, and are free programs.  OBD Diagnostics furnishes the necessary definition files to allow these programs to be used with the MEFI controllers.

January, 2008:

I had pretty much given up hope of getting the original Ram Jet tune out of the MEFI4 controller when I received an email from Bob Radke (OBD Diagnostics) saying that he thought he had the password for the Ram Jet controller and that he wanted me to try it on my engine to see if it works.  Well it looks like the password works.  Now (hopefully) it is just a case of changing the proper IAC parameters and trying the new tune in the Ram Jet.   A comparison of the IAC MAX POSITION settings show that the MEFI3 value is 150 and the MEFI4 is 250.  Hopefully changing the MEFI4 setting to 150 will solve my "cruise control" problem since I did not experience the problem with the MEFI3 controller.

February 21, 2008:

Changed the IAC settings to correspond to the original MEFI3 settings and that seems to have improved my "cruise control" problem.  While I was scanning my engine and with the LM-1 wide band O2 sensor connected, I noticed that the engine is still running somewhat on the rich side at cruise. I guess the next thing will be to try to tune up a few more miles per gallon.

April, 2008:

Well I thought I had a software solution to the cruise control problem, but after many software changes, I decided to put the "plug" back into the IAC port in order to completely solve the problem.

A few comments about the Mefiburn software

I did some research before purchasing software with which to try and fix my “cruise control” problem on my Ram Jet 350 engine and I chose the package sold by OBD Diagnostics (www.mefiburn.com).

As far as I know there are only two other software packages that support the MEFI controllers used on the Ram Jets. One of the others does not even support changing the IAC parameters.  I talked to their "programmer" and he told me  “with our tune you do not need to change them”. Both of the other packages are locked into the controller which they furnish (or they will re-program your original) so that you cannot tune any other controller. I do have plans of perhaps putting one of these controllers on another car that I am building, so having software that could be used on more than one controller was a big factor in favor of tne Mefiburn software.

The thing that finally sold me on this package was the fact that you are starting with the original Ram Jet tune. My engine ran fine except for the “cruise control” thing, so I wanted to at least start with a tune that I knew would work. The other companies claimed that their tunes were developed in house so I was a little leery of them. The cost of the Mefiburn package is also much better than any of the others that I looked into.

April, 2008:

Well I thought I had the cruise control problem solved, but after many software changes, I had to put the "plug" back into the IAC port in order to completely solve the problem.

 

May-July 2008:

I purchased an Innovate LM-1 wide band O2 sensor and I have been logging data from the Ram Jet in an attempt to lean in out at cruising RPM's.  The base GM Ram Jet tune is extremely rich throughout the entire RPM range, ranging from about 12.5 -13.5 at idle, around 13.5 at 1100-1300 RPM and light load (30-50 Kpa), around 14.5 at 1100-1300 RPM and 50-70 Kpa.

I am using the LM-1 analog output #2, which is a voltage ranging from 1v at 10 AFR to 2v at 20 AFR.  This voltage is fed into one of the unused Ram Jet input pins (fuel pressure) and using ScannerPro I can log all of the engine data parameters and the wide band O2 sensor, all in the same data log file. At first I was seeing a high degree of discrepancy between the LM-1 AFR readings and the AFR readings that I was data logging with ScannerPro, sometimes as much as 1.0 – 1.5 AFR points.  I modified the LM-1 analog output signal so that it outputs 0 volts at 10 AFR and 5 volts at 20 AFR. This seems to bring the displayed value and the logged value much closer together, but the logged value still seems to be from 0.1 - 0.2 points higher, which is close enough. Here is a link to how I added the LM-1 wideband output to the ScannerPro data log: www.carols62.com/ramjet/wideband.html

August 2008:

After some more examination of the MEFI4a parameters available under TunerPro, I thought I had found the cause of the "cruise control" problem.   The IAC opens as the throttle opens and closes when the throttle closes so I compared some of the throttle follower parameters of the MEFI4a to those in the MEFI3 and found that some were considerably different. I believe the problem was caused by the IAC under the MEFI4a not closing as fast as it did under the MEFI3. I changed these parameters so that the IAC closing would be as fast as possible, but I still have the "cruise control" problem, although not quite as bad.  In the process I also determined that my original "plug" is probably too thick. I changed the 0.200" thickness to 0.100" and that, along with the software changes, seem to cure the problem.

Just returned from our annual pilgrimage to Corvettes@Carlisle and had a chance to do a lot of tuning on the Ram Jet 350 on the way up and back.  I have the AFR at all of my normal cruise RPM and MAP values up around 14.5-14.8.  My overall average for the trip, including some in town driving, was 29.7 mpg.  

While at Carlisle I met with Bob Radke and we had an opportunity to hook up his software to a Ram Jet ZL1 (installed in a ’67 Corvette convertible).  We were able to download the stock tune from the ZL1, which uses the MEFI3 controller, and (in my opinion) it appears that there is a lot of room for improvement as far as the fuel tables are concerned.  The engine has to be running really rich and the graph of the fuel table is not nearly as smooth as it should (could) be.  Bob asked the owner of the car if he would like to have it tuned better, but he declined, saying that he was going to sell the car at the auction the next day.  

 

June 2010:

After a lot more driving, I am still experiencing the cruise control problem under very unique driving conditions.  When I cruise at 1000-1300 RPM and slightly load the engine for an extended period (say 5-10 seconds) the engine will still fail to slow down when the throttle is closed.  Scanning data indicates that the IAC is still being driven high and the IAC will not return to a low reading for 10-15 seconds, sometimes it even manages to hang up and will not return to idle.  Even setting the MAX IAC position to a very low number (10) will not cure the problem.  So to completely cure the problem I put my "plug" back into the IAC valve seat.   The only disadvantage to this method is that dead cold starts are a little more difficult, but that is a minor problem compared an engine that will not slow down when the throttle is closed.