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Won’t start when warm

K

Ken DG

New member
PLD-PR-L10 (351CID, 240hp, Ford)
Started the season by firing up great in the barn and starting cold. After running and (reaching 150C), or even just starting and shutting down, the engine won’t catch on re-start. It turns over fine, just won’t catch, even with starter fluid.
Some max-throw throttle pumping usually does the trick eventually, but smells a bit rich like it’s flooding.
Runs fine once once it does start (tops out around 40-45). (Doesn’t run like it’s missing a cyllinder).
Wiggling the distributor wires (to maybe improve contacts), got a strong shock through the insulation of one.

Last year I had some starting problems, but they seemed resolved when I found Rec-90 gas without ethanol. Straight Rec-90 this year, and ran through a can of sea-foam carb-cleaner, plus carb cleaner directly into the carb.
 
Replaced the ignition coil & wire from IC to distributor cap. I thought it sounded better and didn’t seem to threaten konking out at idle. Wife did not think it sounded any different.
Shut off the boat after a 400ppm cruise and … not able to restart after I returned it to the slip.
 
I'm looking for help with the same problem. '83 Supra with PCM 351 starts and runs great but won't easily restart after shutting off. Doesn't matter if it's been off for 30 seconds or 2 hours. It takes a LOT of cranking, with or without pumping or holding at WOT. Choke is open. Nothing seems to help, except waiting. It's all tuned up and I just finished rebuilding the Holley - I figured it had to be the carb - but still does the same thing. One other strange thing... often, after cranking awhile, the engine will fire and catch exactly when I shut the key off. If I'm quick enough to flip the key back on and give it a little gas I can keep it running. Could the ignition switch be the problem?
 
have you checked the ignition system for spark during one of these warm start events? the key switch is one of several potential sources of problems here...
 
I have not checked for spark during a warm start attempt. I will, great suggestion. I've been way too focused on fuel delivery.
 
I have my boat in the shop for a carb rebuild, but the mechanic is thinking it might be in the distributer system because mine won’t warm start even with starter-fluid.
Other thing mentioned was the voltage in the start (12v) vs run(8v). I’m not sure what might cause the ignition to opt for “run” just because the engine is warm. Spitballin’.
I’d also replaced the thermal circuit-breaker on the back of my engine which seemed to solve the problem initially, but only for the first couple attempts.
My engine thermostat stabilized the temp at 150, but the breaker trips at 165. It’s mounted above the transmission, so I’m also wondering if the heat exchanger might be degraded and effect the breaker.
It’s sitting in the repair queue now, so hopefully resolved in time to put away for winter.
 
Ken DG said:
I have my boat in the shop for a carb rebuild, but the mechanic is thinking it might be in the distributer system because mine won’t warm start even with starter-fluid.
Other thing mentioned was the voltage in the start (12v) vs run(8v). I’m not sure what might cause the ignition to opt for “run” just because the engine is warm. Spitballin’.
I’d also replaced the thermal circuit-breaker on the back of my engine which seemed to solve the problem initially, but only for the first couple attempts.
My engine thermostat stabilized the temp at 150, but the breaker trips at 165. It’s mounted above the transmission, so I’m also wondering if the heat exchanger might be degraded and effect the breaker.
It’s sitting in the repair queue now, so hopefully resolved in time to put away for winter.
Click to expand...
Vapor lock was suggested, but the lack of spark seems the thing because it won’t start with starter fluid. It just became a matter of “don’t shut it down until your ready to float for a while, then open the cover”.
Also realizing just how poor the airflow is from the front and around the block then out the back.
 
Ken DG said:
...
Other thing mentioned was the voltage in the start (12v) vs run(8v)....
Click to expand...
voltage measured where?
Ken DG said:
...
My engine thermostat stabilized the temp at 150, but the breaker trips at 165. It’s mounted above the transmission, so I’m also wondering if the heat exchanger might be degraded and effect the breaker....
Click to expand...
are you sure its driven by temperature??? if so, temperature measured where - ambient air?
 
Ken, please keep us posted with what the shop ends up doing, and if they can answer Mako's questions above. The thermal breaker thing is interesting. I never heard of that. Thanks guys! I'll try to work a little more on mine but can't until next week. I'll check spark and also try to check some voltages in the ignition circuit, but I really only know enough to be dangerous with the electrical stuff.
 
I when thru the PCM data I have (and the ford marine service data) and there's no mention of any thermal breakers...what part did you use as a 'replacement"?
 
After talking to a local Mastercraft dealer with a pretty good service dept (they won't work on an old Supras because they have plenty of business servicing the brands they sell, but they will give me PCM advice and sell parts) I came away with somewhat of a checklist. After it's warm and won't restart, check for spark (like you said), then check for 12 volts at the purple coil wire. Also check, when running, the voltage drop across the ballast resistor (12v:9v). Lastly, check/compare voltage on ignition switch, start and run wires, during cranking, and while running.
Next time I see the boat, that's what I'll be doing. Or maybe I should just skip the troubleshooting and replace the possibly 40-yr-old coil and ballast resistor. Makomark, I saw you suggested a 12v coil with internal resistor in a different thread. That seems like a good idea.
 
I don't think the circuit breaker behaves the way you described it...given the specs, I'd say that it wasn't the best choice to use in an engine harness...have you measured the current draw to make sure that isn't the issue with the breaker opening? something as simple as a corroded connection can induce all kinds of 'surprises'...

is the '150' you attributed to the engine operating temp in deg C or deg F?
 
Hey guys, just a little update on my Supra. It's still cranking but not starting when warmed up. I've now replaced the coil and the ignition switch. I kept the ballast resistor because the store didn't have it on hand, but I do get a 3v difference during cranking vs run position, which I think is correct. The thing I'm not sure of is the voltage at the coil. I'm only getting about 6v there, at the neg term (with the wire running to the distributer.) Shouldn't it be 12v? I get 12 at the battery and at the ignition switch, but only 6 at the coil. Same whether key is in on position (not running) or while cranking.
The warm-cranking spark seems brighter and more consistent with the new coil (it was barely visible and inconsistent before), but it still seems like it could be brighter - hard to tell though working in the sun.
Other ideas??
Btw, after replacing the coil I had to reset the timing and dwell. Is that normal?
 
changing the coil should not change either the timing or the dwell...

I'd suggest not worrying about the voltage at the '-' terminal on the coil...it will vary with the state of the points when the engine is running.

When you go to start the engine when its 'warm', what is the throttle's position?
 
I see what you mean on checking voltage at the coil being dependent on the points. Makes total sense, as I'll get a full 12 or 13 v if the points land in an open position.
Since I've had this gradually worsening problem for several years, I've tried every possible throttle position while trying to restart, from zero throttle to WOT and all kinds of pumping in between. I used to think the inevitable flooding was preventing it from starting, and waiting awhile to allow the gas to clear at WOT would finally work, but now I think it was just the extra time with the engine cover open finally allowing enough cool down to allow the start. That and the occasional luck of getting ignition as I release the key from the start position to the run position. That just happened again last night while trying to start it warm. With the brand-new ignition switch the still fairly warm engine started and ran with zero throttle as soon as I stopped cranking!

What could that possibly mean? Ignition as the key switches from start to run.

Meanwhile I'm continuing to look for bad connections/wires and thinking I'll try a new ballast resistor.
 
sounds like it may have a bad (or wrong) started solenoid on it....

have you measured the voltage on the "+" side of the coil while going thru the warm restart process?
 
Thanks for continuing to follow and offer help, makomark!

Coil + is seeing just 6v, both when cold and after warmed up, and with key in both run position and while cranking.
Also, when cold I can see decent spark in the distributer points, but when warm the spark is very weak, barely visible. As a test, I clipped a jumper wire directly from the solenoid to the outlet side of the ballast resistor, which then delivered 12v directly to coil +. With that jumper on, the warm engine would easily start. I confirmed a couple of times, running and warming up the engine in between. So I think that means my voltage loss must be either in the ballast resistor or along the purple wire ahead of it, from the key ignition terminal through the harness connectors and to the BR inlet. I'll be trying out a new BR Saturday.🤞 I also put a new set of points in last night, before the jumper test, because I noticed a couple little bumps on the old contact surface, like little bits of weld spatter. The points didn't fix the problem but I felt better about the gap and dwell afterward. I also advanced the timing about 1 degree, because it seemed to run a little smoother.

Another interesting thing I noticed, while cranking the warm engine with the distributer open, right at the instant that I released the key and it flipped back from start to run, I saw a brighter, more normal spark flash from the points. The occasional lucky starting I've mentioned before must happen if I release the key just as the points are opening, and that one strong spark is often enough to get it started. This basically confirms how the lucky start happens, but I still don't know why the coil would deliver that brief surge just as the ignition is switching from start to run.

Let me know if you think I'm on the right track with the ballast resistor and ignition wire.
 
this update isn't consistent with what is in post #17....

I'd say check the voltage at what you call the 'inlet to the BR'...should be battery voltage (maybe less 0.5VDC, for the wires and the connector) ...if not, I'd suspect a voltage drop between the key switch and the coil...with the engine running, the voltage drop across the BR should be a nominal 3 VDC...

also, some marinizers will use a length of resistance wire instead of a ballast resistor...If someone added the BR and the harness has the resistance wire, seeing 6VDC on the + terminal of the coil is very likely...you can verify this by measuring the voltage drop, with the engine running, from the IGN terminal of the key switch to the 'inlet to the BR' - about 3VDC...just like the BR.

The other thing that comes to mind is the slave solenoid...most FORD marinizations use a slave solenoid that will supply battery voltage to the coil when cranking...I don't have a diagram of that particular engine so can't say for sure...it won't hurt if it is the correct type and installed correctly. (on the GM's, the same function is handled by the solenoid mounted on the starter...)
 
The inconsistency between updates is probably in regard to my spark observations. I still think the new coil improved the spark, but now I think it was not enough improvement. Now that I'm consistently checking spark in the distributer I can see that even with the new coil the warm cranking spark in the distributer is not what it should be, while the cold cranking spark is. I know it's a pretty subjective thing and for this kind of a problem it would be more conclusive if I had no spark!

The ballast resistor sees a consistent 11-13v at the "inlet" post with the key in the run position. This drops to about 8v while cranking (maybe because the voltage is being shared with the solenoid and starter?) The "inlet" side has the purple wire coming from the key IGN terminal, plus a wire to the voltage regulator and one to the electric choke. The "outlet" side has one tan wire going to the + coil terminal. The oulet side of the BR has 6v while in run or cranking, but when the engine is warm, that voltage goes up to 13 in run position and 9 while cranking.

I installed the new ballast last night and will be trying it out as soon as the rain stops, but I'm not really sure how it would come into play in the starting circuit.

As far as a resistor wire being added, I'll keep an eye out for it but I'm sure the BR is original installation on the same bracket with the breaker and regulator. Also, I do have the standard Ford slave solenoid setup. Based on how much cranking the engine has been doing through all this the solenoid seems to be doing it's job.

I'll report back after I try the new BR.
 
sounds like your resistor has seen better days...

based on your description, I'd agree that resistance wire is not likely to be present and that the slave solenoid does not have the extra ignition terminal as there's no 'extra' wire going to the coil.

hope it works...
 
No luck with the new ballast resistor. The situation did not change. I've checked voltage at numerous points along both the key IGN circuit (purple) and key SOL circuit (yellow/red). I'm not sure what voltage should be at all these points but here are a few examples.
  • At the key with engine off and cool: In run position IGN=12v, SOL=0v. In start position (cranking) IGN=9v, SOL=9v.
  • Coil voltage + & - is 5v in almost all conditions, except with engine running. Then coil + =8v, which is the "output" from the ballast resistor (BR input is 11v.)
  • While cranking warm or cold, the yellow/red key-SOL wire sees 8-9v all the way from the key, through the neutral switch, to the solenoid-SOL terminal.
  • The purple IGN wire I haven't checked as thoroughly, but the voltage at key-IGN always seems to match the voltage at the resistor input, which is 11-12v while running or cranking, and 8-9v not running with key in run position.
I compared my wiring with a PCM diagram I found online and don't see any discrepancies.
I'm stuck.
 
are you sure the alternator is working?

Dont worry about the YEL/RED wire going to the solenoid - its only for activating the starter and you haven't mentioned that as an issue.

you should see at least 13.6VDC at the key switch (BAT terminal) and maybe a minor drop (-0.1VDC) at the IGN terminal in the run position....and that should be consistent to the ballast resistor....If you think the key switch is an issue, you can bypass it, for testing purposes, with a fused jumper wire between a battery connection and the input to the ballast resistor...of course, you'll have to remove the jumper to turn the engine off with the key switch...

my guess is you have a bad connection/component in the circuit and as it warms up, it resistance goes up (from post #23)....this limits the current and inhibits the operation of the coil (no spark)...measuring voltages doesn't always tell the whole story - unfortunately...

finally, making voltage drop measurements may help in finding the issue...where you measure the voltage across a component (the BR as an example)...it can also help having a printed copy of the circuit while making the measurements and record them directly on that copy...
 
Interesting comment about the alternator. I haven't had any reason to suspect it's not working though. Is there something I should check?

I have 12-13v at the key BATT term, which drops to 11-12 at IGN with key on. All three terminals drop to 9v while cranking. SOL voltage drops to 8v at the solenoid.

I've been wondering about the solenoid, partly because it's a Ford and those solenoids seem to fail often. When I put a 10g jumper from the solenoid battery post to the downstream ballast resistor post I get a full 12v at coil (+) and the warm engine starts easily. But I've only got 8v at that small S terminal. The condensor is just about the only other thing in the ignition system that hasn't been replaced (3 years old.)

Other research has led me to stories of people installing permanent jumper wires from their solenoid's I terminal to coil (+). I don't have any wires on the I terminal, and that makes me wonder how 12v is supposed to get to the coil. It seems the only other route is through the ballast resistor. What am I missing? The diagram below is virtually identical to my wiring, and it also does not use the I terminal on the solenoid. It somehow apparently works.

One other random(?) point, my tach quit working a couple years ago. I just read somewhere that a bad tach should be disconnected from the coil because it can impact the voltage. I'll try that.

1692049032988.png
1692049032988.png
 
You shouldn't see a full volt (1 VDC) change from just switching the ignition switch to RUN...may wanna check all four ends of the battery cables...make sure they are clean and without corrosion...ideally, with tight crimped ring ends...

Normal alternator output should be around 14 VDC, at 1000 RPM, with a decent charge on the battery....depending on the regulator used, it could vary from maybe 13.6 VDC on the low end to 14.4 VDC on the high end...

I don't see any issue using the I terminal on the slave solenoid...it should only provide current when the solenoid is engaged...and its purpose is to supply maximum voltage to the coil during cranking only...in other words, to eliminate the 12 to 8 VDC drop you have seen...

As far as the tach goes, one of their failure modes will 'short out the points' killing your spark...doesn't sound like that's the issue with the tach not working...no reason you can't remove the tach lead at the coil and eliminate that as a contributor...
 
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