AMC 401 / fuel only 454 TBI no start

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yossarian19
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AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

Hi folks,
This is my first Megasquirt project.
It's a bone stock 1975 AMC 401 c.i. V8, Prestolite electronic ignition (blah. But I know it works. Ran when carbed) with a 1989 Chevy 7.4 TBI unit slapped on top.
After calibrating the CTS / IAT sensors, plugging in the MAP hose (hey, we all forget things here and there), turning D2 around, soldering a couple jumpers that had been just sitting there, and putting some gas in the tank, I get 116 RPM cranking tach signal, a consistent cough and try to run, but no engine start.
I am not running an IAC at this point. I have not looked closely at the resting throttle blade position, either, come to think of it.
I recently replaced the head gaskets but have not touched the distributor or mechanical timing at all. I haven't run the engine since putting heads back on.
The cranking pulse enrichment *was* higher, around 300% when really cold, and like an ass I messed with it before writing down what it used to be.
Any ideas? Any information I'm leaving out? I haven't figured out how to datalog yet, not sure how helpful / necessary it is for a few seconds of cranking.
Thanks in advance
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Matt Cramer
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Re: AMC 401 / fuel only 454 TBI no start

Post by Matt Cramer »

To get a data log, go to the Data Logging menu and click Start Logging. You will be prompted for a file name. The log starts when you save the file (this is an easy one to get tripped up on as a lot of people expect saving the file to be what you do at the end of the log). Once you have recorded what you need, go to the Data Logging Menu and click Stop.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

Check for spark? Check timing while cranking? Inspect plugs, wet, dry, fouled? If all is good and plugs are dry add some supplimental fuel manually. I use carb spray cleaner. If it does not fire on that you need to look at firing order, distributor phasing. Weak spark, lack of compression, plugged exhaust, etc.
If it fires on supplimental fuel, look at fuel pressure, fuel quality, injector power, clt. Quick test double req fuel?
Can you see fuel being squirted? Have you made the correct settings for low impedance injectors? The GM TBI unit has a fuel pressure regulator in the back of it that is rebuildable. Verify fuel supply to the correct port (not the return)?
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Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

Had a buddy, ASE master tech + California smog, come by earlier today to look at it with me. We established that all hard parts are functioning correctly, that the engine will run indefinitely if you keep hitting it with carb cleaner and that the injector signal from ECM disappears when it tries to transition from cranking to running.
Looking at the tach signal, it became pretty clear why: at cranking speed it's pretty stable and looks realistic but when it starts firing, it almost immediately starts bouncing from 20,000 RPM down to 2, up to 15,000, all over the place - and it's at this time that the ECM says "Bullshit. No fuel for you!"

So now I'm another "Poor tach signal. Help please!" user. I'm attaching a data log file in case anyone sees things I don't. I think I captured the issue but hey, first time user.
Attachments
2017-11-19_12.20.40.csv
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rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

Resistor spark plugs?

No low resistance plug wires?

Coil mounted on the motor?

PWM current limiting set for your low impedance injectors?
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

Resistor spark plugs - No idea. I can't find the part number I'd ordered a while back. They take the bigger socket and are probably whatever the parts guy would hand you if you gave them year, make and model. This thing came with electronic ignition, so... yeah.
The spark plug wires are similarly not special. I am fairly confident they are carbon core, noise suppression plug wires. I had to guess, I'd say they are Autolite's cheap line of OEM wires, black silicon jacket, 7mm
PWM is set.
Coil is mounted in a pretty typical pinch bracket that bolts to AC compressor bracket & intake manifold.
I also don't have any ground wiring on my shielding jacket. I didn't know that was a thing. Not sure how to fix a ground wire to the jacket, I'm sure I can figure something out. Worst case there are always alligator clips...

Anything else I don't know? I moved the signal wire further away from the plug wires but without resistor spark plugs (?), I think that's a moot point
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

When in doubt, RTFM

I found the following:
13.6 Optional low-z injector PWM modification Some installs using low impedance injectors and PWM current limiting may experience tach noise problems or
processor resets. Try the following noise reduction mods. 1. Cut the center leg on Q9 and Q12 or desolder it so it does not reach the PCB.
2. Run a length of jumper wire from the center leg of Q9 and Q12 to an unused pin on the DB37 connector.
3. Wire this pin to a 12 volt source in the wiring harness, separate from the Megasquirt's power supply wire.
4. Solder a 0.1 uF capacitor in the H1 (boot) header on the main board.

I had also read
5.2.1 Opto-isolator (for coil negative fuel-only triggering):
a) Fit a 36V Zener Diode in reverse into position D2. Note, the Zener Diode must be fitted backwards, so the strip on the diode is the opposite end to the stripe on the main board! (This component is part of the kit from good suppliers)
b) Ensure C30 is fitted. (This is needed for noise elimination) c) Ensure D1 is fitted.
d) Ensure R12 is fitted (390R 1/2W)
e) Solder a jumper from XG1 to XG2. In exceptionally noisy situations it might be required to remove that jumper and instead runs XG1 out through a spare connection on the DB37 and through the wiring harness direct to the engine.
f) Link TACHSELECT to OPTOIN g) Link TSEL to OPTOOUT

But I hadn't taken seriously that my junk might require XG1 to be run out thru the harness and to ground. It is XG1 run direct to the engine GROUND, isn't it?
rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

Doing fuel only as a baby step is two steps backwards, you have to figure out how to get a coil negative trigger to work.
Then when you want spark control you have to go through the learning phase again.

Redundant learning phase, I hope that spot on the wall which you are banging your head on is padded.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

Thanks for the help, buddy!
DaveEFI
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Re: AMC 401 / fuel only 454 TBI no start

Post by DaveEFI »

rickb794 wrote:Doing fuel only as a baby step is two steps backwards, you have to figure out how to get a coil negative trigger to work.
Then when you want spark control you have to go through the learning phase again.

Redundant learning phase, I hope that spot on the wall which you are banging your head on is padded.
Getting a trigger from the coil negative is usually very simple. It is a much larger signal than from a VE sensor. Provided you follow the instructions carefully - and make sure any diodes are fitted the right way round. All the trigger has to do is flash a LED within the opto-coupler.

Fuel only isn't a bad way to start out if the engine originally had a distributor. The fuel map won't be a million miles out if you decide to go to mapped ignition too. It's how I started, and have no regrets.
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rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

All 5 ground wires run from the MS directly to the motor?

See 3.3.1 in the manual, this is vital with low Z injectors.

See also 3.2 particularly sensor grounding. No ground continuity on pin 1,2, or 7 of the harness with the MS unplugged.

Will the motor run on spray cleaner with sane indications in TS (RPM in particular)? If no, unplug injectors and see if that changes indications in TS. This will test if the injectors are causing noise and interfering with the MS.

Don't make assumptions on spark plugs this has burned many MS users. I NEVER trust parts counter help to provide the correct part. Google the number for the plugs installed?
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

Plugs are Champion RN14YC, reported and measured to be resistor spark plugs.
I have all five MS ground wires, plus the ground for the electronic ignition module, spliced onto a 10ga ground that bolts to the AC compressor bracket on the intake. The battery ground cable is bolted to the same location.
I *do* have ground on pins one and two, MS unplugged, while pin 7 looks like an empty pin (?). DIYautotune harness. All sensor grounds go to a ground bus common with the black-white wire from Megasquirt - which should be pin 7 from the diagrams I just pulled up.

EDIT: more testing
I don't know where the ground bus is pinning back to but key on, MS disconnected, it is not grounded.
The negative side of the coil, key on MS disconnected, doesn't light up my probe's "B+" indicator or ground indicator but the display reads 6.5 ... a new one for me.
Last edited by yossarian19 on Wed Nov 22, 2017 9:01 am, edited 1 time in total.
rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

What you have for grounds may work, and I have even done that on some installs.

However the object of the 5 wires is many fine strands will provide a lower resistance path than a single large gauge wire. Think Monster cable.

The low number grounds should have NO continuity to ground with the harness unplugged from the MS. See 3.2 of the fine manual.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

OK, I think I was reading the connector view backwards / mirrored? Looking at the hanging connector's mating surface I have five pins in a row, from top left to right, of ground. I take that as the MS2 grounding wires. Then a handful blank, and nothing grounded thereafter.

I'm going to wire in some injector resistors, turn off PWM and notch back the injector dead time. I think, too, I'll take the manual's advise and run XG1 out thru the header and to ground. Lord willing, I have this thing running by New Years.
rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

If you look closely at the DB connector, most are numbered on the plastic housing.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

Well, the grounds are all wired / numbered as they should be.
I wired in 3.3 ohm 25 watt resistors to eliminate PWM noise as a cause.
Also ran XG1 thru a spare pin and to a valve cover bolt, forgot to check the quality of that ground though.
I've tried a few different noise filter settings & time rejection settings. No joy.
Oddly, it's gone from crank crank start die to just cranking and cranking - it will fire on carb cleaner but I now suspect I'm getting less fuel or zero fuel.
When it did fire, I saw RPM spike to 18,000 again.
MSQ and data log attached.

What are things to try? Could the coil itself be causing noise? Would an old school, wire-in tach filter help here? Really seems like this POS should run, even if poorly.
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2017-12-02_07.37.47.csv
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rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

It seems something in the ignition is scrambling the MS.

If you do a log from the top data logging menu, press start and give it a file name and run it on spray cleaner for a minute, then back to the data logging menu and press stop.

Post the log, it will show what is happening and may give a reason that provides a clue.

I believe there is something in the secondary that is causing sync loss.

I'll ask again about the plug wires, no low resistance spiral wound wires, and make sure they don't have a really high resistance (no more than 50K?).

No burn holes in the rotor and center electrode of the cap in good condition?
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

The wires are plain jane ACDelco 7 mm wires, center lead measures ~7200 ohms.
The cap and rotor are in "fine" condition, not brand new but no problems that I can see. only very minor pitting in the center contact of the cap, the rotor as a shiny spot at the point of contact but no holes worn.
The only thing I can find wrong in the ignition system is the coil being 3.6 ohms across the primaries when spec is 1.8 ohms +- 10% - so i'm putting a new coil in today.
I'll post a data log with the new coil maybe tomorrow AM - with family in town, work, etc I only work on this thing between 530 am and 7, at best.
I really appreciate the help on this, btw.
yossarian19
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Re: AMC 401 / fuel only 454 TBI no start

Post by yossarian19 »

I cranked it over a few times with the data logger running.
I verified i do have red / blue spark against the valve cover and I can see / hear the injectors firing. Will have to clean the plugs and or try new ones to rule out fuel fouling causing the no start. There's no good reason that I should see fuel spraying and not even get a chug out of it when it was doing better weeks ago on the same parts.
No change as I monkey with the distributor timing.
Attachments
2017-12-08_16.51.44.msl
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2017-12-08_17.08.44.msq
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rickb794
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Re: AMC 401 / fuel only 454 TBI no start

Post by rickb794 »

lost sync count 53
peak rpm 31,000

es no bueno
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
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