Dyno problems with MS-2

[Datsun Deron]

Hey guys looking for some possible advice/suggestions here.

Heres the story: Well after getting the MS-2 unit (fuel only with relay board) running with very little problems I decided to take it to the local dyno shop to dial in the VE table. Things went pretty smooth in the beginning we were tuning the 40 KPA portion of the VE table and we worked our way up to 4600 RPM. After holding the throttle at 4600 for about 30 seconds, megasquirt just turned off and the engine died. (the laptop also was not talking with the MS unit). We let the dyno rollers come to a stop started the car up and began attemping to tune again. The same thing happened again after 30 seconds. So we checked the timing at idle, it looked great and we checked the vaccuum also good as well. So then we dialed up the fuel pressure to 40 PSI from 37 PSI and again the same thing happened. We started the car once more and I kept an eye on the fuel pressure guage on my pallnet fuel rail while again holding the car at 4600. The car died again and I didn't notice any sharp changes in the guage.

 

I took the car out earlier today to an abandoned road and attempted to copy the same issue. I drove the car at 4600 in 2nd gear held for a full minute and it wouldn't turn off, I then did it again about 30 seconds after with no luck again. Coming back on the highway I did the test again for a full minute but this time in 3rd gear and still no issue. Today is a fair bit cooler then it was on the dyno day. When we were on the dyno it was about 20 degrees celcious where as today it is 10 degress celcious. I'll have to do the test again as well on a bit of a warmer day.

 

The other things to note are that on the heat sink there may be two potential problems that happened before the dyno.

 

1) R38 used for current limit circuit for driver FET protection began to lift off the heat sink. R38 and R37 both attach with double sided thermal tape. If i pushed on R38 it did still stick it would lift after a couple hours. So I held it down and tacked the edges with some hot glue to keep it down. I did this on both R38 and R37.

 

2) When I was pushing the board back into the case I accidently pushed on the voltage regulator (U5) which is closest to the DB9 port. As a result it did get shifted slightly and now when I push on it, it does move around.

 

As of right now I have't changed anything I'm thinking I should leave it, try again on a warmer day to copy what happened on the dyno as well. Then if I can get the same thing to happen make my adjustments on the heat sink and see if the problem gets resolved.

 

The only other thing that crosses my mind is if vapor lock could cause the engine to die. As previously mentioned I'm running a palnet fuel rail but im not running any heat shield between the intake and header. Today when driving there was airflow under the hood, however at the dyno with their large fan and my hood up I cant imagine much air getting past.

 

Other then what I've mentioned I'm out of idea's to as what the problem might be. I think for the next dyno session I'll keep the screws off the top cover on the ECU so I can take it off completely and possibly set up a fan to cool it off. I think I'll also be fabricating a heat shield for the fuel rail just incase that may be an issue.

 

If anyone else has any idea's or experience with similar issues please let me know so I can get this unit dialed in finally.

 

[naviathan]

You have every circuit in the book installed. If you're only running fuel I wonder what effect all the mixed circuitry would do. I see two diodes that should be jumpered and two caps that shouldn't even be on there. Did you just match the numbers and install everything? I'd go through the book and pull and.or jumper everything you're not using, but the resistors pulling off the heat sink could have had a lot to do with it if they were overheating.

[z-ya]

When you run the car on the dyno, the engine load may more than you could put on it on the street. The dyno load may actually represent more weight than your car. So there is more load on the engine than you could ever place on it on the road. That being said, the more load on the engine, the higher the duty cycle on the injectors.

 

Did you run logging when on the dyno? Do you have more than one ground wire from the MS, through the DB37 cable, to the chassis?

 

Try accelerating up a steep hill to try and replicate the problem. Then turn on logging and post the log results.

[Datsun Deron]

Naviathan - We did most of the steps that were included in the instructions just incase we were wanting to make any changes in the future.

Here's the break down of what I did if it makes any difference.

22. Now you need to make a decision on the first 'optional' component: if you are going to use an IAC stepper motor with MegaSquirt-II, you must install a jumper from the hole marked S12C to the hole marked JS9 (+12C). These are on the bottom side of the board, on the DB9 side of the processor. DO NOT INSTALL THIS JUMPER FOR NON-MegaSquirt-II APPLICATIONS - IT WILL DESTROY THE PROCESSOR!!

-I skipped this step since im not using an IAC stepper motor.

50.

(50a) To install the Hall/optical input circuit (or points without a coil connection)

OR

(50b) For triggering off the coil negative terminal/points: (However, you can only trigger off the coil's negative terminal if you are NOT trying to control ignition timing)

Then you can add the variable reluctor (VR) circuit as an option which included in step 51.

The result of doing step (50a) or (50b) and step 51 means you must jumper between the two options 50 and 51.

 

- For step 50 I installed both curcuits but jumpered for the Hall sensor Circuit. By doing this

For the Hall sensor, optical sensor, coil negative terminal or points:

• Jumper XG1 to XG2 on the bottom side of the PCB, near the 40 pin socket,
  
• Jumper OPTOIN to TACHSELECT on the bottom side of the PCB, near the DB37 connector, opposite the heat sink.

Jumper TSEL to OPTOOUT on the bottom side of the PCB, near the center.

-After step 62 there is another option with for PWM Idle Valve Users. I was not going to be using this option so this was skipped as well.

65. It is choice time again. In this case, you will decide whether to populate the high-current ignition driver circuit.

-With this option you need to follow what ever ignition circuit you are using. In my case I am using the direct coil control, so as a result on its link (http://www.megamanual.com/ms2/vb921.htm) it says I need the high current driver. So I followed the instructions starting at (65a) and went up to (65d). Then it says Note: If you are using the high current driver circuit to control an ignition module instead of a coil directly (and don't want to use the processor port directly - i.e., you have not jumpered JS10 to IGN), you likely need to to add a pull-up resistor

I skipped that because I’m not going to be using an ignition module, so basically I then jumped to step 66.

69. Once again you have a choice to make about whether to install certain components. In this case, you need to decide if you wish to install the PWM flyback damping circuit as well as the standard flyback circuit. The PWM flyback damping circuit is useful primarily for those running pulse width modulation (PWM) with low-impedance injectors. However, it will work fine if you install it with high impedance injectors. If you prefer to install only the standard flyback circuit, skip ahead to step #70: To install the PWM flyback damping circuit:

-Well since the stock Datsun injectors are low impedance the PWM flyback circuit is needed. So I will have to complete step 69 and as it says Even if you have installed the PWM flyback damping circuit, you should install the standard flyback circuit as well (step #70). So step 70 was to be completed also

71. It is choice time yet again. You have to decide whether to install the current limit circuit for driver FET protection. This clamps the current to ~14 Amps, and it is recommended that most people install this. To install the current limit protect circuit

-Well no harm should come of this, nothing wrong with limiting the current in my mind and as it says most people install this so it was added as well.

Those are all the steps I took along the way.

z-ya:

Unfortunately I didn't run any logging on the dyno I was so frustrated with what was going on it didn't even cross my mind. I will definately do so next time I'm on the dyno.

As for ground wires there is only one, Im running a Relay board so from the Relay board I've got one wire that goes from it to a common ground. The common ground spot has a wire that is attached to my intake manifold also.

The load on the dyno was the same as my VE table was showing when I did my street test (40 KPA). But I will try doing the same test going up hill. A buddy brought up the idea last night as well of the injectors possibly getting over heated, I'll check the duty cycle as well on the injectors when I do the test.

[clint78z]

You are correct on hooking up all the components and jumpering the one you need. I am pretty sure the stock injectors are high impedance, but there may be an exception I am not aware of. Anyhow you can run them through the PWM circuit of the injectors.

 

Have you tried hooking it up to the stim and cranking it up to 4600rpm, get a siringe and apply pressure to the MAP sensor. Datalog it this time, it is a great tool to track down problems, typically people try and tune without it which is like minesweeping with a hammer !!

 

It sounds like the problem is external to the MSII, mabey fuiel pump ?? Perhaps you were loosing RPM signal ??

[z-ya]

The stock injectors are low impedance, and require either the PWM settings to be correct, or series current limiting resistors. If neither is done, the injector drivers can overheat, and thermally shut down. Look at duty cycle, if it hit 100%, and you don't have resistors or the PWM set right, the injectors will stop firing when thermal overload is reached. No fuel -> no run -> no RPM in Megatune.

 

Is it a turbo application with stock turbo injectors? If so, you are more than likely hitting 100% duty cycle, especially with the stock fuel pressure regulator.

 

Add two more ground wires (18-20 AWG) in the DB37 cable. Also add two more ground wires from the relay board to the chassis or battery. Remember, the MS provides the ground for the injectors, fuel pump relay, and fan relay. A single 20 AWG +12V wire is fine, but at least three ground wires should be used.

[Datsun Deron]

Well I took it out again today and did a couple passes on a very long hill. I drove it for about 20 minutes doing 1-2 minute runs at 4600 RPM in the 60-70 KPA range. The car still won't shut off. I even pulled over to the side of the road about a minute into my last run. Pulled the top cover off the MS unit (left top plate unscrewed) and felt around inside, nothing is hot to the touch by any means.

 

I watched the duty cycle as well today in megatune (not sure how acurate it is) and it was hitting between 30-40% duty cycle. The car is non turbo and is running stock injectors, I do have an after market fuel pressure regulator and was at 37 PSI when it was on the dyno. Right before the last time it died on the dyno we dialed it up to 40 PSI and the problem still occoured.

 

I might just try doing similar tests on the stim like you said clint78z and see if I get any issues. I fabricated a heat shield today as well to tuck under the fuel rail. Im running an early Z intake with no webbing between the runners, so I'll keep that aside until the next dyno day.

 

Thats a good point z-ya I'll definately add a few more grounds to the unit for extra insurance. As for my PWM settings I have the PWM current limit is set to 18% currently, any lower and when I rev the car it starts to hesitate. Also the Injector open time and PWM time threshold is set to 1.1 as the car dies when the Injector open time is at 0.8.

[clint78z]

To be classified as low impedance injectors they must be below 6ohms approx. These low impedance injectors operate on the peak/hold principle, big current start then hold low current.

 

Now it is true that some z's came with a dropping resistor box, however the injectors are not low impedance peak/hold style. I think they were 12 ohms, can't quite remember. At any rate it would still be a good idea to install PWM injection circuit and use it.

 

If anyone has info to contradict this, please post. We are all here to learn.

[z-ya]

I've measured the resistance of at least 50 Z and ZX injectors, and they all are within 10% of 2.6 Ohms. You need a good quality Ohm meter to measure low resistances accurately. A $19.95 Radio Shack special won't do. I use a Fluke 87 true RMS multimeter. About $350 if you were to buy one.

[clint78z]

I must be mistaken then I thought they were at least 8 ohms, I upgraded to 370cc quite a while ago, so memory is a little fuzzy. The radiohack special should be just as accurate on a measurement like this. It is only in very sensitive low amperage circuits it is nessary to have a high ohm meter like a fluke. The poor ones will affect how the circuit operates by measuring on it.

 

Thanks for clearing that up, I will go home an reverify for myself.

[z-ya]

The quality of the instrument will effect the measurement accuracy. Check the accuracy of your inexpensive meter. It should be listed in the specifications. My Fluke meter has an accuracy of 0.05%. From my experience, low cost meters do not make accurate low resistance measurements. I have a Radio Shack meter also, and it measures 8-10 Ohms for low Z injectors.