420R build 'stalled' at engine start...

[ralph]

Hey, all.  I'm working on the last few build tasks for a 420R kit, and while the posts I've read regarding these symptoms seem to point to the crank sensor, I thought I'd lob my experience out to this forum for opinions.

 

Symptoms:

    Good: 

• engine cranks like crazy
• fuel pump is getting fuel to the rail fine

     Bad: 

• no fuel in engine (so injectors not opening at all -- I 'burped' the air out of the fuel line by disconnecting it at the rail)
• no spark

     Weird: 

• obdc reports a myriad of sensor faults inconsistently, but with themes suggesting low voltage in the ECU control plane, including occasionally reporting more explicitly "<foo> sensor low" or even "low system voltage" after a lot of cranking.  I think some of these could be explained as downstream symptoms -- e.g. baro pressure will be low if the engine isn't firing, right?
• MBE985 cable -> easimap6 reports "Bad crank tooth pattern"...which seems a bit more on point, but I'm not sure what to do about it apart from replacing the sensor

 

I've checked continuity back to the ECU for all plug, injector and crank sensor wires; all checks out, correct pin assignments, etc.

 

There's a sub-plot here that I'm very curious about:  the use of lithium batteries.  Originally, I'd swapped out the stock Banner lead/acid for an Antigravity ATX-20 (680CCA/20Ah).  Then I found this:  https://sbdmotorsport.co.uk/wp-content/uploads/2022/05/Helpful-hints-Battery-Voltage-Issues.pdf and immediately reverted to stock, thinking I'd found the smoking gun.  No dice.  The idea that the starter could starve the ECU voltage-wise made some sense, and I noted that while the CCA metric for the ATX battery is more than adequate, the Ah rating was 2/3 of the stock battery (less overall energy stored), so the SBD article looked like a plausible root cause was indeed the lithium battery....that is, until I borrowed an MBE985 cable from a friend with an ATX-12 (480CCA/16Ah) happily powering his caterham without issues.  To me this suggests that the SBD caveat is probably spot-on for grossly underpowered lithium batteries, but maybe not for the ATX-20. 

 

Until I get this engine running, my plan is to leave the stock battery in place, just to have one less variable, but I'm interested in hearing other folks' opinions on lithium options like the ATX-20.  Apart from the expense, there shouldn't really be any drawbacks, AIUI.

 

As to the current impasse with getting the engine running, I'm going to fiddle with the crank sensor a bit, but apart from the ECU itself, or power to it, I'm kind of out of ideas...

 

 

[JohnCh]

I have that same battery in my car, and it has started a few times with no issues (new build and not yet driven).  What voltage is Easimap showing before you crank and what about while you are cranking?  Does that differ from multimeter readings at the battery?  Is the engine block ground connection ok?  Also, make sure the plug to the ECU is fully seated and verify the crank sensor connector pins are all fully seated within the plugs.  I've seen the latter issue with a different sensor on a 420R engine loom cause some problems. 

 

-John

[ralph]

Good to know re:ATX-20; I'm leaning toward keeping it. 

 

Easimap shows ~13v before cranking, drops to ~9.5v, whilst meter shows 13v/10.5v respectively.

 

In the course of trying to ferret this out, I added a second ground cable (so stock one from bellhousing to chassis bolt hole, and another from an m8 hole on the left front of the engine block to the top sump tank bolt.

 

ECU plug is seated well.  Nothing visibly amiss at sensor plug, main loom coupler or ECU connector.

[ralph]

Flipped the polarity on the crank sensor with a couple clips and some safety wire.  No more "bad tooth pattern alerts", but also no engine start, so I'm not sure that's anything definitive.

[JohnCh]

9.5v sounds a little low.  I know that the Emerald ECU requires a little more than 9v (don't recall the exact value) in order to operate.  I wonder if you are hovering around or below the min mark for the 9A4?  I'll try to check the voltages on my car later today to see if they differ substantially from what you reported.

[KnifeySpoony]

I have an ATX12 in my 420R without issues. 

 

[ralph]

Based on this commentary regarding 'bad crank tooth pattern' being expected on first/last engine rotations (since they are partial), I'm going to bet that the wiring isn't swapped: https://www.sbdmotorsport.co.uk/app/uploads/2020/11/Helpful_hints_when_starting_your_engine.pdf

[JohnCh]

I just checked my car.  Same battery, starter, and ECU as your car, but it's a 2.4L and has 12:1 pistons.  My Easimap and at-the-battery readings were both about 13.2v before cranking, but only dropped to 10.5v.  The only other difference I can think of on my car that could affect this reading is I'm running a slightly larger, 4-gauge 12v+ battery cable.  I believe the stock cable is 6 gauge.  It might be worth double checking your battery connections to ensure everything is up to spec.   

 

-John

[ralph]

I have 2x4awg on ground and stock hot side (with battery disconnect); I suppose I could upsize the +.  Worth noting here (caveats re:lithium notwithstanding) that with the ATX installed all voltage readings, including cranking, were higher.  Might be hairsplitting, but if 9v is nominal for ECU function and the meter read of 9.5v is considered marginal (since it's not instantaneous and may not capture the initial drop when cranking starts), if 10.5v or so (more what I was seeing with the ATX) isn't considered marginal, I should be good cable-wise, yeah?

 

 

[fastg]

If you think you have voltage issues attach a jump box or jump cables to a second battery. That will give you extra capacity. 

 

Just a suggestion. 

 

Graham 

[JohnCh]

One thing to be careful of is that Antigravity specifically states not to use it in conjunction with a normal battery.  Relevant section from the user manual:  

 

"COMPATIBILITY. The product is only compatible with 12-volt stock systems in vehicles. Do not attempt to use product with any other types of batteries or in series or parallel with another battery, or interior electronics could be damaged. Use with, or Jump starting other battery chemistries may result in fire, explosion, injury, death or property 
damage. Contact the battery manufacturer prior to attempting to jump start the battery. Do not jump start a battery if you are unsure of the battery’s specific chemistry or voltage."

 

You're using the stock cables, so they should be more than sufficient.  If it is wiring related, it could be a damaged wire or a poor/dirty connection somewhere.  I'd go through the entire system, including the battery disconnect, with a multimeter and see if resistance is higher than expected at any point.  Another possibility is a duff battery.  Might be worth asking AG.  

 

-John

[ralph]

if by "conjunction" you mean in parallel as suggested above, yeah, I wasn't going to do that.  I have ample current to crank the engine and unequal voltage batteries in parallel is a general no-no.  I would think that as separate supplies (one for the ECU, one for the starter, etc.) that would be ok, but I'm not finding info on how to separately power the ECU. It's suggested in several places (including SBD's docs), but I'm not sure how to do it.

[JohnCh]

10 minutes ago, ralph said:

if by "conjunction" you mean in parallel as suggested above

 

yep, just wanted to call that out in case you were going to give that a shot.  I forgot that you mentioned the Banner is doing the same thing.  It's unlikely you have two duff batteries, so ignore my comment.  Given the Banner is back in place, and you have the voltage drop info when cranking with that battery, maybe reach out to Caterham's build support alias and ask if that is an issue?  They might have some troubleshooting ideas.  I've found that Lee is helpful with oddball questions.  

[MV8]

I don't know much of anything about your electrical system. I don't believe it is a battery issue. I suggest turning the key to the run position and manipulating the trigger to cause fuel/spark to occur as a test without engaging the starter.

[ralph]

Theories are thinning out....anyone in the bay area have a known working standard spec 420 ECU sitting around?...

[MV8]

Using the 2015 420 assembly guide engine harness layout (no actual schematic), BY11 = GND, WR73 = start SOL, WO = B+ in run/start.

[KnifeySpoony]

I have one installed in my car but it has the roller barrel tune on it...

[KillerB]

Hey Ralph, it's Brian; we picked up our Cats on the same day last Nov. I also had some 'teething' pain upon engine start a few months back. Engine did start sometimes, but ran super rough and no rev. Troubleshooting revealed not getting 5V at TPS, thus the ECU had no idea where throttle position was. Turned out to be an ECU connector assembly problem; not all sockets on multi-pin connector were locked into place. Definitely check connector and verify all socket barrels are locked into place properly, otherwise they will back out when connector is attached to ECU.
Regarding battery being a problem, that's a red herring IMHO; especially if engine turns over without issue. I installed similar battery: Scorpion SSTX12Q-FP.....works great, plus it's only 2 lbs!

[ralph]

 

I think this is a good call, and probably what Rich was driving at in our many exchanges on the topic.  I did do continuity checks from the ECU connector, and ruled out wiring issues in that path; as you observed, the female side of the ECU connector could show good continuity, but if the barrels unseat when connected to the ECU itself, those results are spurious.  The weird part is it's not one sensor, it's all plugs/injectors getting fractional voltage; it's not obvious to me how one or two loose barrels could do this.  I'll pick that apart that connector today.

 

RE: battery, completely agree, but leaving things stock for now until I isolate the fault(s).

 

Glad to hear your build went well.

 

Thanks, Brian! 

[ralph]

I may have made some progress narrowing this down.  Looking for what's in common with all injectors and plugs, there's the white/purple wire.  It doesn't go to the ECU, AFAICT, it goes to a relay.  If I test voltage from the back of the engine loom connector from an injector's red wire to the white/purple on the loom connector, I see .23v.  If I leave the test lead on that red wire and move the white purple to the fuse where it appears to terminate, I see 12v.  This makes me think that there's something funky with the relays/fuses/wiring thereof, and all this poking around with the loom and ECU connectors was off base.