MPS Inductance Curves and Tuning, Is Fuel Injection Corp USA Selling Rebuilt MPSs with Bad Transformers? Options

[Cessnaporsche01]

Thanks for the input, all!

Olympic, I'll definitely take you up on your offer - it should provide a definitive answer as to whether I'm dealing with bad MPSs or not. That curve looks very healthy. You've also reminded me that I have the same cam profile as you! WebCam 9590 - you mentioning the number made me remember it shared its number with the processor my PC was running at the time lol

Adolimpio, that's a handy calculator you've made there - I'll be sure to use it if I can get to that point. Although, I'm only about 600ft ASL where I live, so not a ton of altitude compensation for me.

Emery, I did check my injectors. I'm still running my stock dizzy though, since it seems perfectly healthy.

Chris, I may send my FIC MPSs to you for check over/repair, regardless of outcome with Olympic's unit - I could sell them to recoup some costs if nothing else.


And for everyone, I wanted to highlight this experiment I did yesterday, since the thread is moving around a lot. I don't believe this is a tuning issue. Based on this behavior, there are 2 options as I see them: Either (1) the MPS transformer is damaged/broken to the point that it cannot provide pulse width necessary for WOT, or (2) something else in the EFI system is causing inadequate fuel delivery. At the moment I'm leaning toward Option 1, since I've double, triple, and quadruple checked everything except the MPS, which is displaying odd traits, and is missing at least one original component.

Before posting this, I had an idea, so I actually just tried out popping the disassembled MPS into the car, with no cells or diaphragm, just the core extended out to its absolute limit, which is further than it probably should be, since this MPS seems to be missing the little tabs that engage the core stops.

The primary secondary coil reads 1.066H in this configuration. The car starts up immediately, pretty stinking rich but not too smoky, and responds very well to throttle input. But full throttle - even ~80% throttle - still kills it. Like, this MPS CANNOT PHYSICALLY provide any more pulse width, and it's still not enough fuel.

[TJB/914]

Thanks for the input, all!

Olympic, I'll definitely take you up on your offer - it should provide a definitive answer as to whether I'm dealing with bad MPSs or not. That curve looks very healthy. You've also reminded me that I have the same cam profile as you! WebCam 9590 - you mentioning the number made me remember it shared its number with the processor my PC was running at the time lol

Adolimpio, that's a handy calculator you've made there - I'll be sure to use it if I can get to that point. Although, I'm only about 600ft ASL where I live, so not a ton of altitude compensation for me.

Emery, I did check my injectors. I'm still running my stock dizzy though, since it seems perfectly healthy.

Chris, I may send my FIC MPSs to you for check over/repair, regardless of outcome with Olympic's unit - I could sell them to recoup some costs if nothing else.


And for everyone, I wanted to highlight this experiment I did yesterday, since the thread is moving around a lot. I don't believe this is a tuning issue. Based on this behavior, there are 2 options as I see them: Either (1) the MPS transformer is damaged/broken to the point that it cannot provide pulse width necessary for WOT, or (2) something else in the EFI system is causing inadequate fuel delivery. At the moment I'm leaning toward Option 1, since I've double, triple, and quadruple checked everything except the MPS, which is displaying odd traits, and is missing at least one original component.

Before posting this, I had an idea, so I actually just tried out popping the disassembled MPS into the car, with no cells or diaphragm, just the core extended out to its absolute limit, which is further than it probably should be, since this MPS seems to be missing the little tabs that engage the core stops.

The primary coil reads 1.066H in this configuration. The car starts up immediately, pretty stinking rich but not too smoky, and responds very well to throttle input. But full throttle - even ~80% throttle - still kills it. Like, this MPS CANNOT PHYSICALLY provide any more pulse width, and it's still not enough fuel.

Mr. Cessnaporsche01 & 914ers.
If interested I'll send you my OEM (new) MPS to test your 914 motor activities, but you must send it back to me with no adjustments or modifications. (see Photo)
This would be helpful details for the 914 guys on this list
Send me a PM with your ship address if interested. Just promise to send back.
Tom in Michigan .

[emerygt350]

Don't discount those trigger points. That could easily be causing your lean condition. The 123 really is the most fabulous thing...

[FlacaProductions]

The 123 really is the most fabulous thing...

Don't tease me like that - i'm back to my 123 install in 10 days...

[adolimpio]

Has anyone considered checking the TPS?

If not working properly the ECU may think the engine is idling and will not consider the MPS input properly.

[emerygt350]

Yes, a good idea. You can check that without removing it.

[rick 918-S]

Here is a dumb question... Have you checked your fuel pressure? You seem to be in the range of Andres settings and have made other corrections suggested. If your fuel pressure is off or fluctuating or dropping you could have the same condition at WOT.

[Cessnaporsche01]

TJB, thanks for the offer. I'm going with Olympic's MPS for testing, but your offer is most appreciated.

Emery, I tested my trigger points with some LEDs in circuit with the injectors, and I'm quite comfortable that they're not skipping. That said, the 123 is still on the horizon for when the car is back on its proverbial feet.

Adolimpio, TPS is good. It's got the 914Rubber board, but I tested and calibrated it while messing with the intake system, and it does what it's supposed to.

And Rick, yeah, I have a pressure gauge in line in the injector loop. I have it set a little high, around 32psi, since that's where I used to run it, but it's rock steady.


I should be getting Olympic's MPS in the mail on Friday. If it gets me WOT, I'll know what's been plaguing me. If not, welp, another run down the old Dr-DJet checklist like a madman, I guess lol. I'll report back with results.

[Cessnaporsche01]

Well dang. I can rule out the MPS as the root cause. The car goes right back to its start-no-run behavior with Olympic's installed.

What this has taught me is that my LCR meter cannot measure the coils in the MPS - it reads his at .927H @ 0inHg, when it's actually 1.49H. So that explains the incorrect MPS readings. It's weird that the primary coil reads proportionally, when I know it can measure a sub-100-Ohm inductor accurately, but maybe that's to do with it being in a transformer and not free standing? Regardless, behavior is unchanged between 3 MPSs, so I'll call them all innocent.


I popped the 043 back in, and added a 370 Ohm resistor to the CHT, just to crank the mixture right up there and went for a drive so I could get video of the behavior. The resistor allowed me to get more throttle in than ever before, like, close to ~90% WOT, but it still sputters wide open, and of course, the idle mixture is pretty filthy rich - mild amounts of brown smoke out the tailpipe while idling. Engine is at temperature in the video.

The engine sputters whenever my foot is on the floor, but it recovers instantly when I let up. I should have thought to do it in the video, but the engine will redline, just at lower throttle settings, so I'm pretty sure the injector points aren't the culprit. I'm thinking is has to be pulse-width related, but I'm coming up blank on what could be causing the pulses not to scale proportionally with the MPS signal. Maybe shitty injectors?? And that doesn't answer why the engine doesn't want to idle below a fairly high MPS
setting - although that may just be tuning, since it will idle at a full inner screw rotation below max.

Anyone heard one of these engines sound like this before?

https://youtu.be/WSK4shNqZiE

It sure does seem happy in the part-throttle regime.

[Superhawk996]

I was taking CHT measurements at from the harness junction to chassis ground. Like you, it was around 3500 Ohms on a cold engine at 70ish degrees ambient. For the same temperature, both of my CHTs alone, out of the engine, read more like 2500.

Did this ever get resolved?

[Cessnaporsche01]

I was taking CHT measurements at from the harness junction to chassis ground. Like you, it was around 3500 Ohms on a cold engine at 70ish degrees ambient. For the same temperature, both of my CHTs alone, out of the engine, read more like 2500.

Did this ever get resolved?

Not sure if there's anything to be resolved there. I think the 3500 Ohms (which I measured on the cold engine again today, with an ambient of 55F) was just because the block was colder than the ambient air. I went and checked since you asked about it, and it measured 1500 Ohms with the engine still noticeably warm from having been out on the road a few hours ago. Chassis ground at battery to harness ground on block has only 1.2 Ohms of resistance, and the CHT connection at the harness to the harness ground on the block measures the same as to the battery ground, so there's not a big resistance anywhere that there shouldn't be.

[Superhawk996]

I was taking CHT measurements at from the harness junction to chassis ground. Like you, it was around 3500 Ohms on a cold engine at 70ish degrees ambient. For the same temperature, both of my CHTs alone, out of the engine, read more like 2500.

Did this ever get resolved?

Not sure if there's anything to be resolved there. I think the 3500 Ohms (which I measured on the cold engine again today, with an ambient of 55F) was just because the block was colder than the ambient air. I went and checked since you asked about it, and it measured 1500 Ohms with the engine still noticeably warm from having been out on the road a few hours ago. Chassis ground at battery to harness ground on block has only 1.2 Ohms of resistance, and the CHT connection at the harness to the harness ground on the block measures the same as to the battery ground, so there's not a big resistance anywhere that there shouldn't be.

1.2 ohms of resistance isn’t insignificant from one ground reference to another.

Is this resistance in your meter leads? What does your meter read when you simply short the leads, one to another?

Resistance between battery negative and engine should be zero (after accounting for resistance in your test leads).

Not saying this is the root cause but issues like this need to be resolved. The ECU depends on having proper ground reference for input signals such as MPS, CHT, TPS. Etc.

[technicalninja]

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

If I found a 1.2 ohm ground plane difference in the metal substructure I'd run dedicated cables to specific ground points throughout the car.

I did this once to a 79 Fiat X19 (in the top ten list for wonky electronics).

Wife drove it for 80K without a single electrical gremlin.

I'd fix the grounds FIRST!

More than 50% of the time electrical gremlins are ground related.

Which makes sense when you realize the electrons actually flow from negative to positive... (IMG:style_emoticons/default/ninja.gif)

[Ishley]

Listening to your car run.... have you changed out the Throttle Position Sensor? When I first got my car running I had issues until I installed a new board. Just a thought.

[Cessnaporsche01]

I did some testing for resistance around the car this morning. Superhawk, good call on checking my meter probes, as they were measuring 0.2-0.5 Ohms shorted to each other. I scrubbed them with scotchbrite and was able to get the short resistance down to 0.1-0.2 Ohms. Getting a good dig into the metal on the case and ground bolts saw resistances under 1 Ohm. Most of the resistance seems to be in the block and transmission case, since the transmission ground strap reads 0.1 Ohm, and the ground strap mount to the battery ground is only 0.2 Ohms, but from any of the engine bolts to the strap it's more like 0.5-2 Ohms, with the fan cowl resisting at a massive 15 Ohms, not that any electrical components are attached to that. All the metal is quite clean, so I don't know if there's anything I could do to reduce resistance further, other than ground the engine loom straight to the battery like Ninja suggests.

Ishley, yes, I did replace the TPS board with a new 914Rubber one. It's calibrated correctly, and I don't feel any of that rough bouncing between throttle positions that indicates a bad board.

[Superhawk996]

All the metal is quite clean, so I don't know if there's anything I could do to reduce resistance further, other than ground the engine loom straight to the battery like Ninja suggests.

You really should be measuring 0 ohms after compensating for what ever your test leads add.

Personally I wouldn’t accept any more than 0.1-0.2 ohms between battery neg and engine ground lug that FI is grounding to. Battery cables (either pos or neg) can appear good but be corroded internally adding resistance. The ground weld stud at the body (under trunk) may be getting dicey 50 years in. Modern cars have begun to move away from spot welded ground studs due to corrosion and increasing resistance as they age causing CAN bus issues.

As suggested by Ninja, I would use a temporary jumper to get a 0 ohm ground over at the FI ground lug. This could be as simple as a temporary jumper cable for troubleshooting on a drive. Get any possibility of poor grounds out of the equation. If it doesn’t improve anything it’s simple to remove.

[Superhawk996]

As an aside, listening to your video I’m not convinced that you don’t have an ignition related misfire going on.

Ignition and fuel issues are so commonly mistaken one for the other.

Very hard to relate to the video since I don’t have a good sense of speed, load on the engine, and how the throttle is being modulated.

But can hear that it does seem to run better at what is probably lighter load and less throttle, less RPM.

Did ignition timing ever get set properly? At one point you said you couldn’t even get enough revs to verify ignition advance.

[Cessnaporsche01]

Fair enough on the resistance thing. I doubt a few dozen milliohms is the issue, but it's not much trouble to run a temporary wire to battery ground.

And the ignition theory is interesting. Although, wouldn't that be more RPM dependent than throttle position dependent? Like not enough dwell to charge the coil? I guess the advance is moving up a few degrees when manifold pressure goes to 0, so I could test with the vacuum retard hose disconnected and see if anything changes.

But otherwise, the timing is set to the notch at 3000rpm - once I got the mixture richened up on the MPS it gave me the full rev range so I was able to tune it no problem.

[windforfun]

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

If I found a 1.2 ohm ground plane difference in the metal substructure I'd run dedicated cables to specific ground points throughout the car.

I did this once to a 79 Fiat X19 (in the top ten list for wonky electronics).

Wife drove it for 80K without a single electrical gremlin.

I'd fix the grounds FIRST!

More than 50% of the time electrical gremlins are ground related.

Which makes sense when you realize the electrons actually flow from negative to positive... (IMG:style_emoticons/default/ninja.gif)

And the holes flow from positive to negative.

Bad common ground = floating voltages = bad behavior.

[emerygt350]

During this troubleshooting I would disconnect both advance and retard on the dizzy if you haven't already. Plug the ports on the TB of course.