Jump to content



Terrible RPM spikes while cranking


  • Please log in to reply
17 replies to this topic

#1 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 29 November 2019 - 03:17 PM

I have been battling these RPM spikes for over a year now. I still can not get my new MPI build to crank consistently...The RPM spiking during cranking causes ASE and WUE to turn on sporadically even though the car hasn't cranked yet..The RPMs are ALL OVER the place while cranking....So I am flooding the engine every time I attempt to crank it...

I have documented these problems in my restoration thread here:

http://www.starquest...c=152437&st=140


So I re-did the wiring from the dizzy to the VR cable and its very clean and everything is soldered and heat shrinked...

The dizzy does have the tiniest bit of play in the rotor, so you can rotate it slightly if the cap is off. But there's no way that tiny amount of play gives me these massive spikes during cranking.

Speedyquest, I took your advice and re-did my grounding.

As you can see, my engine block has 4 grounds going to it...

Posted Image
Posted Image

Guys, please help me. I'm at the end of my patience. I've fought these RPM spikes for over a year. I still haven't been able to drive this rebuilt engine/MPI build because of this problem...

Any suggestions of where to check for noise or something else?

Edited by Preludedude, 29 November 2019 - 07:24 PM.






#2 speedyquest

speedyquest

    Established Member

  • Members
  • PipPipPip
  • 4,217 posts
  • Gender:Male
  • Location:La Crosse Wisconsin
  • Interests:bmx, cars, computers
  • Model:Starion

Posted 29 November 2019 - 05:34 PM

Have you done a high speed datalog for the trigger wheel? If not you need to do that to see what's happening. One of the common things that also effects a clean rpm signal is how close your sensor wires are to high power current. So things like coils, alternator, starter, etc put out tons of electrical noise and can effect your sensor readings.

1987 Flatty Starion -- Widebody Conversion -- V-Mount Setup --  JDL Tubular Manifold  --  MX-6 Intake -- MS3-Pro -- AEM FPR  --  ARP head studs -- 3" hood exit exhaust -- Hahn Racecraft 16g --  Tial F38 Wastegate -- Tial Q Bov -- Short route piping -- 5 lug & LSD conversion -- Tubular Front End -- Manual Steering Rack Conversion -- Manual Brake Conversion -- Stack Digital Dash -- AEM UEGO -- D2 coilovers -- full GNT poly bushings & mounts -- four 8" rears -- car lightened significantly...  More to come!


Posted Image


Build Thread --->  http://www.starquest...opic=143564&hl=


#3 tsi_tom

tsi_tom

    Established Member

  • Members
  • PipPipPip
  • 2,403 posts
  • Gender:Male
  • Location:Quakertown, Pennsylvania
  • Model:Conquest

Posted 29 November 2019 - 06:12 PM

My thoughts if they mean anything:

In your ground to the block picture above, it doesn't look very clean.  The factory bolt is shiny and has a serrated washer.

Is it possible the sensor is bad?  Can you measure the resistance?

With these setups is a capacitor necessary to filter the spikes?
Engine
20 over forged pistons
Stock injection system

My restoration project: The Missouri Project

#4 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 29 November 2019 - 07:23 PM

View Posttsi_tom, on 29 November 2019 - 06:12 PM, said:

My thoughts if they mean anything:

In your ground to the block picture above, it doesn't look very clean.  The factory bolt is shiny and has a serrated washer.

Is it possible the sensor is bad?  Can you measure the resistance?

With these setups is a capacitor necessary to filter the spikes?

Its clean...I sanded the block well, and use a wire brush on bench grinder to clean the bolt threads and head...

What sensor are you referring to?

Edited by Preludedude, 29 November 2019 - 07:25 PM.


#5 tsi_tom

tsi_tom

    Established Member

  • Members
  • PipPipPip
  • 2,403 posts
  • Gender:Male
  • Location:Quakertown, Pennsylvania
  • Model:Conquest

Posted 29 November 2019 - 08:24 PM

Isnít there a Hall effect sensor for crank position?
Engine
20 over forged pistons
Stock injection system

My restoration project: The Missouri Project

#6 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 29 November 2019 - 09:38 PM

Iím not running a crank trigger guys....Iím using a locked distributor.

#7 tsi_tom

tsi_tom

    Established Member

  • Members
  • PipPipPip
  • 2,403 posts
  • Gender:Male
  • Location:Quakertown, Pennsylvania
  • Model:Conquest

Posted 29 November 2019 - 11:13 PM

So that uses the stock pickup coil?

Edited by tsi_tom, 30 November 2019 - 08:27 AM.

Engine
20 over forged pistons
Stock injection system

My restoration project: The Missouri Project

#8 Turbo Cary

Turbo Cary

    Established Member

  • Members
  • PipPipPip
  • 1,770 posts
  • Gender:Male
  • Location:Charleston, South Carolina
  • Model:Conquest

Posted 30 November 2019 - 07:45 AM

Are you using a tach adapter? Also what are your engine state settings in Megasquirt?

#9 scott87star

scott87star

    Technically Challenged, Daily.

  • Vendors
  • PipPipPipPip
  • 5,025 posts
  • Gender:Male
  • Location:Mandan, NORTH DAKOTA
  • Interests:Freezing, thawing, thunderstorms and constant wind.
  • Model:Starion

Posted 30 November 2019 - 11:11 AM

He's using one of my 88-89 plug and play systems, it uses the stock ignition pickup although it runs through a new twisted pair shielded wire from the dizzy to the ECU, grounded at the ECU.  No tach adapter needed.  There are lots of these systems out there working well, I've never seen a noise issue like this.

Mark, if I remember correctly, we did a round or two of noise filtering without success, correct?  The noise filtering tends to be hit or miss, it either works like magic or doesn't help and I recall adding some to your system but maybe that was back when it was still TBI?
Now selling true plug and play megasquirt!  Absolutely the best value in stand alone ECU's out there.

I can upgrade your Fuel Injection Pro firmware

Performance Coatings!  Pistons, manifolds, bearings and more!

Now a graduate of EFI University!  www.efi101.com

ECU Vendor link:  http://www.starquest...howtopic=137426

#10 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 30 November 2019 - 11:58 AM

I think we did, but we can try again....Iíll send you an email with the current tune.....

#11 scott87star

scott87star

    Technically Challenged, Daily.

  • Vendors
  • PipPipPipPip
  • 5,025 posts
  • Gender:Male
  • Location:Mandan, NORTH DAKOTA
  • Interests:Freezing, thawing, thunderstorms and constant wind.
  • Model:Starion

Posted 30 November 2019 - 02:00 PM

The other thing to review is the rotor phasing.  A distributor has both low voltage and uber high voltage going on in the same space and if the rotor phasing is off, meaning the dizzy is off a tooth or two, you can get the high voltage going to the wrong place, like the rpm input.  To check you'd put the crank at 25 degrees BTDC #1 compression stroke and then take the cap off the dizzy, the rotor should be pointing directly at the #1 tower.

The surest way to eliminate any cross talk between high and low voltage is to change to a crank trigger, also provides much better timing resolution.
Now selling true plug and play megasquirt!  Absolutely the best value in stand alone ECU's out there.

I can upgrade your Fuel Injection Pro firmware

Performance Coatings!  Pistons, manifolds, bearings and more!

Now a graduate of EFI University!  www.efi101.com

ECU Vendor link:  http://www.starquest...howtopic=137426

#12 ucw458

ucw458

    This will mean the extinction of all life forms on this planet.

  • Moderators
  • PipPipPipPipPip
  • 11,645 posts
  • Gender:Male
  • Location:Colorado
  • Model:Conquest

Posted 30 November 2019 - 02:08 PM

On your shielded wires are they grounded at the engine and the ECU?  If so that creates a ground loop that can cancel out the shielding effect and let noise in.  Shielding should only be grounded at one end.
My 87
Posted Image

#13 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 30 November 2019 - 02:44 PM

 ucw458, on 30 November 2019 - 02:08 PM, said:

On your shielded wires are they grounded at the engine and the ECU?  If so that creates a ground loop that can cancel out the shielding effect and let noise in.  Shielding should only be grounded at one end.

So which shielded wires are we talking about?   Where are they located?

#14 ucw458

ucw458

    This will mean the extinction of all life forms on this planet.

  • Moderators
  • PipPipPipPipPip
  • 11,645 posts
  • Gender:Male
  • Location:Colorado
  • Model:Conquest

Posted 30 November 2019 - 05:22 PM

Usually wires that have a low voltage signal that can be affected by EM fields.  For example, O2 sensor, ignition signals, knock sensor.  Particularly your wiring between the distributor and ECU.  The stock pickup produces a very low voltage signal around 1-2 volts iirc.  Any outside noise on that wire could cause issues.  Looking at the FSM it appears the negative side of the distributor pickup is grounded to the engine.  If you have it grounded at the ECU as well that would create a ground loop.

Maybe your battery cables coming from the trunk are causing issues.  This only happens when cranking..  Those cables are passing significant current when cranking.  If then are next to signal wires they can induce noise.  Maybe try removing the battery from the trunk and connect it in the engine bay as a test to see if the RPM signal clears up.
My 87
Posted Image

#15 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 30 November 2019 - 05:36 PM

So the dizzy has 3 wires on the connector.   The black/yllw wire (ground) is wired into the VR shield wire.

Does this black/yllw wire on dizzy connector need to be grounded on the engine?  And not wired into the VR cable....???

#16 psu_Crash

psu_Crash

    Advanced Member

  • Members
  • PipPipPipPip
  • 7,230 posts
  • Gender:Male
  • Location:Lawrenceville PA
  • Interests:400+ WHP 450+ WTQ!!... and curves with green eyes
  • Model:Starion

Posted 30 November 2019 - 10:50 PM

No. It sounds like that is just the shield wire for the twisted pair cable. That should only be grounded at the ECU end.
Are you getting battery voltage spikes at the same time as the RPM spikes?

Edited by psu_Crash, 30 November 2019 - 10:52 PM.

'86 Starion, MPI with MS2extra, Ebay To4E 57 Trim (in testing), P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods,AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
2016-17 SCCA Solo Glen Region Champion in Street Modified. Going for a 3-peat this year ;)
The Valencia Project
http://www.starquest...+golden +dreams
My Feedback Link
Posted Image

#17 Preludedude

Preludedude

    Established Member

  • Members
  • PipPipPip
  • 3,167 posts
  • Gender:Male
  • Location:Upstate, SC
  • Model:Conquest

Posted 01 December 2019 - 07:07 AM

Iím wondering if the battery relocation is the culprit.  

My TBI didnít have cranking issues back in July2017 before it blew a head gasket at drag strip.  

Now after the tear down and rebuild, I went MPI and kept Scottís MS system.....now Iím having rpm spikes during cranking.

Found this informative site while googling issue:

https://www.w8ji.com..._to_battery.htm

Seems I shouldnít have 4 grounds all together that are directly tied to battery post....

Edited by Preludedude, 01 December 2019 - 07:28 AM.


#18 psu_Crash

psu_Crash

    Advanced Member

  • Members
  • PipPipPipPip
  • 7,230 posts
  • Gender:Male
  • Location:Lawrenceville PA
  • Interests:400+ WHP 450+ WTQ!!... and curves with green eyes
  • Model:Starion

Posted 01 December 2019 - 05:54 PM

That's correct. One solid ground is all you need. I run from the battery negative, to MS, to a block mounted on the frame rail near the stock battery location. One heavy wire from that to the block. I can't remember 100% about my sensor grounds. I believe all or most anyway are grounded back to MS. With this setup I would get random RPM spikes under load that coincided with battery voltage spikes. So what I did was install a power filter on the MS 12 volt feed. Problem solved.
I'm sure something in the battery location grounding is the culprit. Although I never went back to figure it out ... yet.

'86 Starion, MPI with MS2extra, Ebay To4E 57 Trim (in testing), P&P head, OS SS Valves, Wiseco +.030, ARP head/rod, RPW Roller Cam, Crower Rods,AEM H2O/Meth Injection, Mighty Max CAS 4 Direct Fire Wasted Spark, BSE, Tial 38mm, JDL exhaust mani, HKS turbo timer and EVC3, AEM UEGO, 3" DP into 2 1/2" Dual Exhaust, 85# Delphi's, Magna modded by Chad, Accufab FPR, Walbro 255, D2 Coilovers, GNT Poly Bushings and mounts, Autopower 4 point cage, Funk-Lock, LED Tails and Dome ... etc^4
2016-17 SCCA Solo Glen Region Champion in Street Modified. Going for a 3-peat this year ;)
The Valencia Project
http://www.starquest...+golden +dreams
My Feedback Link
Posted Image




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users