A9L on 94 engine, no priming injector pulse?

[Wallyman]

Simple question, should I see a priming pulse on injector 1 using noid light at key on with engine cold?

Trying to resolve a cold start issue, will not start without starter fluid. 2-3 rounds of this and it will start to run on its own, and once warm will restart normally. Noid light on injector #1 shows injector pulses during crank but not a prime pulse prior to crank. Setup details:

1995 Miata chassis
1994 SN95 engine with 87k miles, all stock: internals, TB, intake, MAF, injectors, fuel rail, fuel pressure regulator
1989 wiring (Engine, EEC, O2) harness (modified for 94 TPS pigtail, no other changes).
A9L EEC IV
New Autolite 25 plugs, gapped at 0.052
New distributor cap and rotor
Mustang Fuel pump circuit not used, Miata fuel pump runs at key on.
Return fuel system, brand new fuel filter
Air intake temp sensor added to #5 runner (like an 89 would be)
EGR and related removed, head holes plugged, TB hole plugged
Air pump & related removed
Shorty swap headers
No O2's installed (yet, exhaust not built yet) but wiring harness is connected and hanging. O2 harness is correct manual transmission version.

Additional info:

Battery fully charged
94 TPS mounts elongated and position adjusted to 0.95v with KOEO (Initially had 1.27v, and code 23 - Throttle Position Sensor Out Of Self Test Range. Hot idle was 1100rpm. After adjustment, voltage in line with 89 specs, and hot idle is 600rpm)
Fuel pressure at prime is 40psi, measured at stock 5.0 test port on rail. Pressurizes on key on to 'run'.
Verified good grounds to pins 20, 40, 60 of EEC.

Current codes:

• 31 - EGR Valve Position/Pressure Feedback EGR Circuit Below Minimum Voltage. 0.24 volts
  • EGR system removed, so this makes sense.
  • (Have ordered 82 ohm resistor to make eliminator to clear CEL.)
• 67 - Park Neutral Position Switch Circuit Open; A/C On -Manual, Manual Lever Position Sensor Out Of Range/A/C On (CM,O), Clutch Switch Circuit Failure
  • The clutch switch is not hooked up, so this makes sense.
• 81 - Secondary Air Diverter Circuit Failure
  • Air system removed, so this makes sense.
  • (Have ordered 82 ohm resistor to make eliminator to clear CEL.)
• 82 - Secondary Air Bypass Circuit Failure
  • Air system removed, so this makes sense.
  • (Have ordered 82 ohm resistor to make eliminator to clear CEL.)
• 84 - EGR Vacuum Regulator (EVR) Control Circuit Failure
  • EGR system removed, so this makes sense.
  • (Have ordered 3.9K/390 ohm resistors to make eliminator triangle to clear CEL.)
• 85 - CANP Circuit Failure
  • Canister & purge not installed, so this makes sense.
  • (Have ordered 82 ohm resistor to make eliminator to clear CEL.)
• 87 - Primary Fuel Pump Circuit Failure
  • not using 5.0 fuel pump circuit, so this makes sense.
  • May add +12v feed back top EEC to get rid of this code.. could this be the issue?

I've run through the crank/no start checklist and didn't find anything (can post my results if needed)... the only thing that seems suspect is the last Code 87 maybe but then why would it run after it's warmed up?

Any thoughts appreciated!

 

[General karthief]

The injector will only pulse when the engine is cranking or running, as far as I know.
fuel pressure?

 

[Noobz347]

What is initial timing set to?

 

[Noobz347]

87 - Primary Fuel Pump Circuit Failure

• not using 5.0 fuel pump circuit, so this makes sense.
• May add +12v feed back top EEC to get rid of this code.. could this be the issue?

This [could] be an issue(?)

I do not recall what, (if anything) waits on this circuit to change.

If it's starting though, even with starting fluid, then it should start/fire anyway.

 

[Mcmahst]

I don’t think your no start is related to the 87 code. The injectors need + voltage, a ground, and the PiP signal from the ECU to fire. I looked through my Probst book on the code 87, and the ECU does not disable any engine start or run functions. If it’s got 40 psi fuel pressure, a spark, AND the injectors are firing, it should start. So, since it needs the starter fluid to do so, cold, it could be low compression, etc stuff. Just more things to drive you crazy.

 

[General karthief]

Monitor fuel pressure during cranking.

 

[Wallyman]

The injector will only pulse when the engine is cranking or running, as far as I know.
fuel pressure?

Prime fuel pressure 40 psi at test port, using stock 94 rail, injectors and FPR, plumbed as return system.

What is initial timing set to?

Unknown, bought as a pullout from a running car so assumed (ugh) stock. will check next round of troubleshooting and repot back.

I don’t think your no start is related to the 87 code. The injectors need + voltage, a ground, and the PiP signal from the ECU to fire. I looked through my Probst book on the code 87, and the ECU does not disable any engine start or run functions. If it’s got 40 psi fuel pressure, a spark, AND the injectors are firing, it should start. So, since it needs the starter fluid to do so, cold, it could be low compression, etc stuff. Just more things to drive you crazy.

Well, it has +12, noid light shows injector 1 fires while running (and cranking for that matter). I can check compression but how likely is that given it starts and runs fine warm? You may get a single pop on first rev of the 1st crank (30-40% chance roughly) but after that it's not a single one, just starter cranking. After the 1st or 2nd round of starter fluid you start getting a couple cylinders lighting off during crank, and eventually enough hit that it will run on it's own rough then clean up pretty quick as it warms up. Reminds me of a carb motor without a choke, or a flooded motor that is clearing cylinders (but it doesn't smoke like that is the case).

Monitor fuel pressure during cranking.

Will do and report back.


The source of the question is the stock Mazda motor primes on key on, which I assume(d) is a normal scenario for a non-carb car. I've got a couple of them with aftermarket ECUs and priming pulses are always a thing that, if wrong, makes starting hellish or downright impossible.

One thing I pondered was the motor sat stored indoors for a year, perhaps dirty injectors...?.. but the fact it will start and run warm implies they can't be too terrible or it wouldn't do that properly... right? I'm hoping to finish the exhaust this weekend and I can take it out and hammer the hell out of it and see if it falls on it's face or if I have fuel pressure issues under full load.

Couple other things:
Engine coolant sensor seemed to be reading hotter than actual.. like 105-110F when it was 70 in the shop. I replaced that, now it reads as expected but no change. (Was hoping reading hotter meant less fuel being sent on prime/crank causing the issue.. but nope).

Once running hot, unplugging the IAB solenoid will stall it out, as will unplugging the MAF. so those appear to be working. The MAF is closer to the TB that recommended due to the packaging of a Miata engine bay, about 5-6" from the TB but I doubt that would prevent it from starting at all, would it? I can probably cobble something longer temporary to test to get it the 12" out I read is the recommended but I've seen it this close before so that seems a stretch.

 

[Wallyman]

Sider question - any value to doing a base idle reset? Cuz hot without IAC unplugged, it dies I believe so something seems off there.

https://www.allfordmustangs.com/threads/how-to-do-a-base-idle-reset-and-how-to-check-and-set-your-tps.340926/

 

[General karthief]

Have you tried cranking with part throttle or flat on the floor?

 

[Wallyman]

PROGRESS!

Wanted to try the base idle thing, so unplugged the IAC (having read that on a base idle reset thread), and cold cranked.... it started!! Now it barely idled, so I turned stop screw out more (more open, about a full turn) and was able to get a very steadish low idle, probably 500rpm (didn't have working a calibrated tach yet and honestly wasn't expecting it to start so I didn't have the dwell/tach meter hooked up)

It still stumbled with any throttle stabs other than a very slow opening, but one problem at a time, I guess. I had 40 psi at KOEO, and on that low idle was seeing 30 psi running but I noticed the test port connection leaking so had to pull it off. I can get better numbers later to confirm but I think fuel pressure is ok (followup, 40 KOEO and 30 psi once it started with a solid 820rpm idle)

I feel like this confirms I need to set base idle as a starting point, so the plan is this (which I am doing right now):

Hook up fuel pressure gauge without leaks (done)
Hookup tach/dwell test box (done)
Go through base idle set per that allfordmustangs link (copied here for ease of reading).. almost done! Green steps are completed, yellow are my notes, red are things I can't do yet.:

Ok so, if your having idle issues and you have ruled out everything else to include your tps voltage, vacuum leaks...etc, follow this step by step.

1. Disconnect your negative on your battery to clear/reset your computers memory. caution when ever you disconnect your battery remove the negative first then positive, reconnect in the reverse order, if you dont you can possibly cause a battery explosion or destroy your computer. Leave your battery disconnected for at least 30 mins to let the capacitors in the ECM to discharge fully.

2. Disconnect the IAC connector.

3. Reconnect your battery.

4. Start the motor, with the IAC plug disconnected.

5. Set your idle, via the stop plate screw on the throttle body, between 650-850 rpms, it is best to set it at the lowest setting to prevent idle problems, such as surging, rolling etc.

Set it at 650, I could go a little lower but it started hunting, at 650 it only wavered 10rpm on the analog meter.​

6. Turn the motor off and reconnect the plug on the IAC.

7. Start the motor at let it run for 2-4 mins at idle with all accessories off, if the motor stalls out or the idle drops to low repeat steps 4-6.

Started right up, idles at 820 +/-10. Stabs of throttle it revs, and drops to 1000ish, then settles down to 820 repeateable. (once this is all sorted, going to look at a DIY IAC restrictor plate to get revs to drop quicker).​

8. Once your idle is good, turn the motor off and wait 2 mins, then start it back up and run for another 2 mins with all accessories on.

Restarting it fires pretty quick, idle goes to 1100rpm for 30 seconds or so then slowly drops as expected. All accessories not really an option at this time.. no headlights installed, no HVAC, etc (reassembling a gutted shell). But for now I think I am on the right track.​

9. Check your TPS voltage. It should be at .98v if not refer below on how to set it.

Checked, it was 0.98 now 1.035. Not changing it as I think that gives enough headroom and using the 94 TB/TPS it was a lot of hole elongation to get that, not sure I can go much further and still have a place for the screw.​

10. If your idle and TPS are good, allow 10-20 mins to let the computer "relearn" under normal driving conditions.

I'll get to this in a few days once the exhaust is built, and maybe I install a seat and the dash. ​

It appears to be a throttle plate that was too closed (and I did try cranking with throttle slightly pressed, wouldn't do it. Guessing with the TPS being out of adjustment when I did it @ over 1.25v maybe that is why).

I will finish up the exhuast, get the O2's installed and then do another round of cold start with everything connected and see if it's good to go or not. I did some additional reading and found there is a different procedure for a 94-95 (which this engine is) that involves setting the throttle stop and then adjusting the IAC screw for the bypass air instead. I'll post that up in a moment... I'm guessing it's another way to skin the cat and perhaps i ought to go that route since this engine has the ability to do it.

 

[Wallyman]

What I did appears to be for a pre 94 car that doesn't have the IAC bleeder like the 94/5 so the only way to do it (aside from using the Ford IAC fix, which you can get here: https://lmr.com/item/LRS-9939A/1986-93-Mustang-50L-58L-Idle-Air-Control-Iac-Adjuster) was to adjust the thottle stop to open the throttle plate.

This is the process I found that is 94/95 specific. The two yellow text highlights are the key parts.

Try resetting your idle with the following procedure. If your idle problem is NOT being caused by a bad part or vacuum leak then I have never seen this not fix the problem!​

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Begin with a cold vehicle. The idea here is to get the car to a firm cold idle with enough air bleed capacity left in the idle circuit for IAC adjustment.​

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The idle stop should be set first. Back out the idle stop screw, away from the bell crank arm, until about 1/2 turn past the point where it no longer makes contact (blade fully closed). Using a 0.010" feeler gauge, tighten until gauge just drags between screw and bell crank arm. Remove feeler gauge. Tighten screw exactly 1 1/2 turns. If the screw is very loose, put a drop of loc-tite or silicone on it, so it doesn't work out of adjustment.​

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Now remove the connector to the Idle Air Controller (IAC) just on the other side of the throttle body. Start the car and allow vehicle to warm for 2 minutes. Give a small "blip" to let it settle. If it is having a hard time staying running you may have to get an assistant until you can get to the front of the car. Now open or close the air bleed screw (CCW opens) next to the IAC until the car idles at 575 to 600 rpm. For guys with aftermarket cams and an EEC tuner, you might want to idle a bit more briskly, say 650 to 675.​

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(Can't find a good photo, but the screw should be located under the white goo/plug/cover, between the two "A" callout lines, and uses a small allen to adjust apparently, I haven't tried yet):

Obviously, this rpm range is by what the car and driver wants...IE, no set idle speed, whatever works for YOU.​

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Turn off the car. Now count the number of turns clockwise to close on the idle air bleed screw. If it falls between 1/2 and 2, it's okay, now reverse it out the same number of turns. Log the number somewhere in case you need it for the future. Reconnect the IAC. You are done.​

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If the air bleed screw is above 2 turns, it's a good idea to tighten the idle stop screw another 1/2 turn, and then repeat the idle setting. If it is below 1/2 turn, then loosen the idle stop screw by 1/4 to 1/2 a turn, and repeat the idle setting. Be sure to put another drop of silicone RTV on the stop screw if it was disturbed. Reconnect the IAC.​

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Now remember we adjusted the set screw on the throttle body. That means that the voltage reading from the TPS sensor has changed. It should read between .96 and .99 volts. Anything outside of that range will cause all sorts of issues including misfires and rough idle.​

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you will have to back probe the TPS connector. With the connector attached to the TPS stick a paper clip into the rubber boot on the connector where the top and middle wires go into the connector. The rubber is very flexible the paper clip will slide in between the rubber and the wire.​

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Set your multimeter to volts. Turn ignition to ON. Then place your multimeter leads on the metal pins. If it comes up as a negative that is okay as long as you are -.96 to -.99. If you get this reading then great you are done and hopefully your issues are gone. If not proceed to step 9​

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This is where and extra pair of hands come in handy. Using a large screw driver you will need to loosen the bolts that hold the TPS. DO NOT USE A SCREWDRIVER THAT IS TOO SMALL BECAUSE YOU WILL STRIP THE BOLTS. They probably will be really tight so you have to really lean on the screwdriver and use some finesse.​

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Once the bolts are loose you will need to move the TPS up or down and continue to read the voltage. Once you get it to the desired setting you can retighten the bolts. What I do is I find .97 and then as carefully as possible I tighten the TPS down. what will happen is the voltage will change usually to .96 or .98 but that it okay. Once you are done with this manually open the throttle body a few times and close it then reread the voltage and make sure it is still within our desired range.​

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Depending upon how loose your set screw was you might want to cover it in RTV to hold your setting. At this point you have CORRECTLY reset you idle.​

Reading it over, I think the boiled down answer is this: What I did wasn't wrong, pre se, but rather incomplete. Instead of just adjusting the stop screw for bleed around the throttle plate, instead I should have set the stop screw at a fixed point (1.5 turns - 0.010") and then adjust the bleed via the IAC adjuster (hopefully between 1/2 and 2 turns open). Same end result, but guessing Ford changed it to this approach for a reason so I ought to follow. The blue text is the key.

Am I interpreting that correctly?

 

[Wallyman]

Reading it over, I think the boiled down answer is this: What I did wasn't wrong, pre se, but rather incomplete. Instead of just adjusting the stop screw for bleed around the throttle plate, instead I should have set the stop screw at a fixed point (1.5 turns - 0.010") and then adjust the bleed via the IAC adjuster (hopefully between 1/2 and 2 turns open). Same end result, but guessing Ford changed it to this approach for a reason so I ought to follow. The blue text is the key.

Am I interpreting that correctly?

And to close the loop, I misinterpreted the wording on the bleed screw location. After digging up a few youtubes on adjusting an SN95 specifically, I see there is a screw on top of the TB that was plugged on my TB with a painted-the-same rubber plug, so it looked like a casting. I did the procedure as outlined above, adjusting it as stated and the car starts and idles perfectly cold and hot.

Now to move on to the next issue.. perfect idle but stumbles on any throttle.... new thread for that.