How to test MPS, I think it is not working Options

[surfdogskier]

So before I go ballistic and switch over to dual carbs, I just want to check one more thing. The only thing I can see that I see could be the reason my injectors are not firing is due to the MPS.

Is there a way I can check to see if the MPS is working properly using an ohm meter or other device? I see the wire on the MPS has the numbers 7,8, 10, 15. I would like to check the continuity of these wires as well. Where is the other end locate?

Thanks

[BeatNavy]

A bad MPS shouldn't cause injectors not to fire. But to your question, there are two basic tests:

1. Continuity tests of primary and secondary coils. Using an ohmmeter, you check continuity between terminals 7 and 15, and then between 8 and 10. You should get roughly 90 and 350 ohms, respectively. The terminals are there in the 4 pin connectors. So put one lead from ohmmeter on one terminal and the other lead on the other terminal. Do that once for primary and then once for secondary coils.

2. Vacuum check -- using a vacuum gauge (e.g., mityvac), pull a 15 psi vacuum and make sure it doesn't leak down more than a few psi in a minute. If it does, the diaphragm is probably ruptured, resulting in a rich condition.

Here's the reference: https://members.rennlist.com/pbanders/manif..._sensor.htm#MPS Diagnostics

I know you have a separate thread about injectors not firing, so I won't speculate here about causes in this thread.

Good luck. I like FI, but I know it can be frustrating when not working (IMG:style_emoticons/default/sad.gif)

[JamesM]

A bad MPS shouldn't cause injectors not to fire.

(IMG:style_emoticons/default/agree.gif)
Most common failure of MPS is diaphragm failure which causes the ECU to see full load and thus run very rich.

Always good to test your MPS, but specifically for injectors not firing I would check, in order.

1. Injector grounds. (these ground at the center line of the engine case towards the rear of the car)

2. FI trigger points

3. Wiring harness

4. The ECU itself (no real easy way to test without swapping it out)

This assumes you are talking about the injectors not getting a pulse electrically. Mechanically there are other factors to consider like no fuel pressure or gummed up injectors. (im not sure if your conclusion that they are not firing was based on an electrical test or just pulling one to see if it squirts)

things to consider:

1. Can you hear the fuel pump prime when you first turn on the key?

2. Key on/slowly opening the throttle from the engine bay, can you hear the injectors click (should be ~10 times to full open)

If #1 fails than you need to look at pump/relay/ECU
If #2 checks out than grounds/wiring are at least somewhat functional and you should focus on trigger points/ECU (provided #1 also passed)

[dr914@autoatlanta.com]

do not give up! If you send us your control unit and manifold pressure sensor we will check for free, do it all of the time for customers

[Highland]

1. Continuity tests of primary and secondary coils. Using an ohmmeter, you check continuity between terminals 7 and 15, and then between 8 and 10. You should get roughly 90 and 350 ohms, respectively. The terminals are there in the 4 pin connectors. So put one lead from ohmmeter on one terminal and the other lead on the other terminal. Do that once for primary and then once for secondary coils.

How close does terminal 8 and 10 have to be to 350 ohms? I'm getting 327 ohms. Terminal 7 and 15 measures at 89.5 ohms.