[guitaristanime]

Anyone with a walbro fuel pump that has log files of cranking?
I'm curious to know what voltage you read during cranking.

Mine is as follows:

 

[indykid]

What makes you suspect the fuel pump is pulling the voltage down? Where are you logging your voltage?

 

[guitaristanime]

What makes you suspect the fuel pump is pulling the voltage down? Where are you logging your voltage?

Because I don't know what else it could be. Do you have some suggestions?

That log file is from tuner studio, I've also video'd the multimeter whilst cranking, the results are very close, not much difference between the two figures.

However my question is more around whether the above is actually good/bad and I wished to compare it other people with the same set up really to see if perhaps this was the issue. The reason I thought it might be the FP is because I'm aware they pull a lot more current than a stock one and people often complain the stock relay melts (which happened to me)

I'm all ears if there's other things I can check that might be pulling down the voltage.

EDIT: is a voltage of 8.5v low for cranking?

 

[Martin Y]

I think my cranking volts can get down into the 9's but 8.5 sounds kinda low. Have you checked the quality of the ground connections?

PS I do have a Walbro pump but it was provided with my supercharger kit long ago and I don't know if it's a 225 or 190.

 

[atlex]

also check with a known good battery.

 

[indykid]

The starter motor will be drawing a damn sight more current than the fuel pump.

I'd try a known good battery as atlex suggests.

Speed is proportional to voltage in a DC motor so if you're seeing fuel issues, it might be related to the pump running at 3/4 speed, though cranking fuel flow shouldn't tax it compared to demand at WOT.

 

[guitaristanime]

The starter motor will be drawing a damn sight more current than the fuel pump.

I'd try a known good battery as atlex suggests.

Speed is proportional to voltage in a DC motor so if you're seeing fuel issues, it might be related to the pump running at 3/4 speed, though cranking fuel flow shouldn't tax it compared to demand at WOT.

Thanks

Zero issues at wide open throttle, it's just this weird laboured cranking and sometimes losing sync. Fuelling is fine, my car is currently continuously priming on ignition and that also has no interruptions.

I have a new map to try today with different trigger edge settings as it was mentioned that sometimes "falling edge" can cause this behaviour.

My next port of call is either a new crank sensor or a new battery, I haven't decided which yet.

 

[guitaristanime]

I think my cranking volts can get down into the 9's but 8.5 sounds kinda low. Have you checked the quality of the ground connections?

PS I do have a Walbro pump but it was provided with my supercharger kit long ago and I don't know if it's a 225 or 190.

Thanks, I haven't actually checked them myself - but they were checked by the person that did my engine swap in July last year. Perhaps I should review, thanks for the suggestion.

Though I would suspect any ground issues to affect other things, like when using the car generally.

 

[Martin Y]

Well, cranking pulls a couple of hundred amps through some connections so it's several times the current flowing in normal running. Even a slightly poor connection could drop a couple of volts in that situation and seem pretty normal the rest of the time. Really, the only two grounds that take that major hit are the battery terminal itself and where the other end of the battery ground lead bolts to the powerplant frame. (Under the car in front of the rear right wheel, you can peer straight in and see where the crimp eye on the end of the cable bolts to the PPF right next to the diff. For some reason the cable is inclined to fray and fracture there.)

 

[indykid]

Thanks

Zero issues at wide open throttle, it's just this weird laboured cranking and sometimes losing sync. Fuelling is fine, my car is currently continuously priming on ignition and that also has no interruptions.

I have a new map to try today with different trigger edge settings as it was mentioned that sometimes "falling edge" can cause this behaviour.

My next port of call is either a new crank sensor or a new battery, I haven't decided which yet.

Laboured cranking is likely voltage related, 'losing sync' could be related to microcontrollers in the ECU browning out from the low voltage.

Two failure modes linked to low voltage, I'd be checking the high current connections and trying a new battery before I worried about the crank sensor, unless you have a known good one to swap in. If you're strapped for cash and it's one or the other, a friend's car and some jump leads would prove out the battery issue.

I've just stuck a DMM on my battery and from 12.29V with the ignition on, it only dropped to 10.5V while cranking...

 

[atlex]

at higher revs your alternator is up to speed and shoving out 14.7 volts or so, if it's healthy, it's lower revs, i.e. cranking revs, when your alternator can't cover for a failing battery.

 

[Martin Y]

Mind you, if that was 10.5V measured at the battery it could still be a volt less when measured at the ECU, even if all the connections are good.

(I did a quick Google on expected voltage drop and found 125 - 150 amps seems to be typical for cranking a 4 cylinder engine. The ground cable is 16mm² and about 1.8m long, and at 125-150 amps it would drop over 0.5V from end to end. And that's only the ground cable; you'd drop voltage in the 12V cable too.)

 

[guitaristanime]

Mind you, if that was 10.5V measured at the battery it could still be a volt less when measured at the ECU, even if all the connections are good.

(I did a quick Google on expected voltage drop and found 125 - 150 amps seems to be typical for cranking a 4 cylinder engine. The ground cable is 16mm² and about 1.8m long, and at 125-150 amps it would drop over 0.5V from end to end. And that's only the ground cable; you'd drop voltage in the 12V cable too.)

Based on what you've said, I have pretty much expected voltage drop then, thanks. I do think a stronger battery would help though.
I tried the battery from my NB (Panasonic one from Mazda, which is about 3 years old maybe) measured very similar voltages, but under cranking it did dip slightly less, what I do know is that the battery in this car is very cheap and the CCA is around 340a which surprised me. Capacity is only 40a too.

I have a weird set up, my car was originally an automatic car. Ever since I went to an MS3 Mini, the fuel pump continuously primes, I have been advised this is something to do with the way the AFM is supposed to control the fuelling but not really sure I understood the technical reasons behind it.

So I am removing this from the equation by wiring the fuel pump relay wire back to the ECU. Don't know the technical reason why it continuously primes and why the ECU can't control this but perhaps once it's done it will help the situation some...

 

[Martin Y]

That rings a bell. On the original 1.6 the fuel pump relay isn't connected to the ECU. It's powered while cranking and then after that it's kept powered by a switch in the airflow meter (which stays on so long as there is some airflow). That's supposed to be a safety cutout so if the engine stops (in an accident or whatever) the fuel pump stops.

I don't know what complications being auto adds or what mods might be done to let you remove the AFM.

 

[guitaristanime]

That rings a bell. On the original 1.6 the fuel pump relay isn't connected to the ECU. It's powered while cranking and then after that it's kept powered by a switch in the airflow meter (which stays on so long as there is some airflow). That's supposed to be a safety cutout so if the engine stops (in an accident or whatever) the fuel pump stops.

I don't know what complications being auto adds or what mods might be done to let you remove the AFM.

That last line is important, no one seems to know but on the contrary, I haven't heard of anyone else having issues with an auto-converted car and there's plenty out there. Hell there's people making a business out of it.

 

[guitaristanime]

Going to upgrade my battery from the one on the right today to the one on the left, not expecting it to solve the problem but the battery I have is clearly very old and the CCA is very low.

I have some TE Multilock pins on order so that I can complete the re-wire of the fuel relay into the ECU harness.

I know the Battery ground at the actual battery is OK as I'd already replaced the wire there at the end. However I wasn't aware of the anchor point under the car, took a peek just now and the bolt that goes into the PPF is very rusty and the area around the bolt looks a bit green. Will get under the car today and clean that area up.

Is the bolt just a normal zinc coated anti corrosion one? Or does it need to be brass coated?

 

[Martin Y]

I think it's a normal bolt. You just need to check the contact surfaces of the ring terminal and PPF and underside of the bolt head aren't corroded, and that there aren't many fractured strands where the cable is crimped into the ring terminal.

 

[guitaristanime]

New battery seems to have done a world of good... video attached of 3 starts in a row!

Still takes a few cranks more than I'd like but I'm shocked how much difference its made and I'm happy. Perhaps just need a touch more fuel now?

 

[guitaristanime]

@Martin Y @indykid

I wonder if I might pick your brains, I already have various people looking into this issue including the guy tuning my car and hopefully Dan from BOFI but I'm beginning to get desperate and I know the collective hive mind here has a wealth of knowledge, I knew something wasn't right, call it gut feel.


Long story short, the final piece of my tuning puzzle was to get the fuel pump to stop being perma-priming when ignition was on. I had already re-wired the fuel pump to it's own relay with the live feed straight from the battery and the relay opening and closing using the signal from the original relay. Works fine as is, pump runs constantly and car starts and works OK (albeit a few cranks more than I'd like but I think that's just MX-5s)

We already discussed the nuances of the AFM/1.6 challenge and why the pump primes this way, the lack of ground on the AFM circuit during ignition causes it to need to get ground from somewhere else (or something like that)

Looking at wiring diagrams we know the fuel pump is supposed to be on pin 2T on the ECU harness.

Well documented and confirmed by Reverant himself on the MS forums, any non early immobiliser car, the right two pins (which includes the fuel pump pin that's been used on 2T and a middle ground pin) is the correct bridge to use:

A continuity check between the documented fuel pump (right) pin on the board and the pin on the ecu connector shows thats working great, 1ohm.

With the car on ignition, the ground (middle) pin, grounds for 2 seconds (priming pulse) and then goes open. With the car running, the ground pin provides constant ground - however it pulses extremely quickly, almost quick enough to miss until I used an audible tone....... (first issue? thoughts?)


When I try to start the car with this set up, the pump primes as it should on ignition and then stops. I then try to start the car, it catches immediately and then dies.

Tuner thinks the pump isn't running once the car starts, but we've proved the ground pin is closing the circuit as it should and the car gets as far as catching so should move to running phase.... (second issue, thoughts?)



EDIT: sorry I should add to stop the pump running constantly, I had to take the green wire from the relay harness, chop it and feed the 2T from the ECU harness to the green wire on the FP relay harness.

At this point it still ran constantly, until we chopped the purple wire, it seems the purple wire is perma-grounded.

EDIT 2: ECU is MS3 Mini for a 1.6 car, the car has a VVT engine in.
Car works and runs fine. This is just the final piece of what has been a long year.

 

[Martin Y]

First thought is the 2 seconds priming will pressurise the fuel rail and that probably means there's enough fuel to start the car. That could be all the fuel you're getting. So it may be the pulsing effect you saw on that ground pin while running isn't enough to drive the FP relay. I think it needs to be established if that's normal. It sounds as if there's some kind of PWM drive signal on that pin there when perhaps it ought to be a solid ground. MSEXTRA forum is where I would go to ask.