89 Bronco stumbles on start–put a new Chinese’s ICM there-$12.00 -Do you think that’s the problem–once it gets going it is fine all day—It is just the first start in the morning–fuel pressure ok
Pay the $86 for a Ford Motorcraft Module. That will answer your question.
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Does that mean the problem would be a weak spark due to a poor quality ICM?
Can someone crank it while someone else watches one of the spark plug wires for spark to see if the ignition is cutting out when it is first started with the stumbling problem?
Cold starts require a much richer fuel/air mix, and some ignition modules may also boost to the spark voltage. So it could be a faulty ignition module that’s not boosting the spark. However the fact that it runs ok after the engine warms up could point to a problem with the coolant temp sensor function, so double check that’s working correctly. The drivetrain computer (ECM) is responsible for enriching the mixture and telling the ignition module to boost the spark for cold starts. But if it doesn’t realize the coolant is cold, it won’t know to do that.
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George, thanks for the information–my Bronco is an 89—when you say ECM–you’re talking about the EEC-IV computer.? The coolant temp sensor, I put in new–and it reads good–I also changed the ICM–one I had earlier that worked ok, and got rid of that $12.00 one------------I did something else and that is I installed a hotter coil–one that puts out 48,000 volts—I started it the other day and it was much better–bear in mind here in AZ it’s 105 degrees—It never ran so smooth and transmission shifting was much, much better. I do think the EEC-IV could be changed–but I’ll drive it for a while as the computer has a habit of fixing itself----keep you updated! ----Sam
Ignition modules function two modes.
These are the start and run modes.
When starting the engine, the ignition module is in the start mode which allows full battery voltage to the coil to ensure the cold engine can start when the fuel mixture is richest.
Once the engine starts, and ignition switch moves to the run position, the ignition module switches to the run mode.
The ignition module then reduces the voltage to the coil.
This is done so that when the engine starts and the charging system comes on line, the voltage from the alternator doesn’t cause the coil to send too much voltage to secondary ignition components and burn them up.
This takes the place of the ballast resistor/wire found in older ignition systems.
So, the ignition module may be faulty where it doesn’t provide the proper voltage to the coil when starting the engine, but does once the engine is running.
Tester
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Yes, good point–the racing coil I put in there was designed for the EEC-IV ford system–to put out that extra voltage --really made a difference in start and idle and run–so smooth you definitely notice the difference.
ECM == electronic control module. Common name for a car’s drivetrain computer. On newer cars often called PCM == Powertrain Control Module. I’m guessing EEC-IV == Electronic Engine Control version 4, which would perform a similar function. ICM == Ignition Control Module, which is also a computer, but smaller and mostly related to the ignition system spark delivery, so has fewer functions. Auto manufacturers are not required to name their parts using the same convention.
Since it runs better with the higher voltage coil, pretty good clue the problem was either the ICM or something else spark related. I presume your 89 Bronco ignition system is configured as distributor/single coil. If so, besides the ICM, spark problems could be caused by the distributor cap/ignition rotor, the spark plug wires/boots, or the spark plugs/gaps. Power and grounding problems possible too. Of the two, grounding problems more likely. Make sure to visibly check the engine to chassis ground connection, and the battery negative to chassis connection, make sure both clean, no corrosion. If there’s cylinder head/intake manifold ground connections, checks those too.
I’ll check the chassis grounding points—I did replace battery negative wire—I was also thinking of the distributor --Car has 204,000 miles , I have new plugs and wires----The car used to start like even before you touched the key—fast–and high idle for less than a minute and then idle—I’m sure this 105-115 temps would affect that, and it never gets cold here until February–if 50 is cold-at night. On start, if you just tap pedal, it takes off—I put a new TPS in as that came up on the code reader.–Thanks for all the help !
I have an early 70’s Ford truck, 302, always a quick starter. About two years ago, wouldn’t start at all. Cranked ok, but wouldn’t catch and run. Fuel system tested ok, spark present during cranking, but looked a little more orange-ish than I expected. Turned out the ignition point resistance was the problem, 5 ohm. Should be less than 1 ohm. No visible indication of point surface contamination or oxidization, but cleaning the point’s contact surfaces returned it from a no-starter to a quick starter.
Points? There’s still a car out there running with a breaker ignition? That technology went out 50 years ago. Better notify @Old-Days-Rick, he will want to come out and inspect the truck to see if it has drum brakes too! 
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Yes, I owned and work on aircraft–clean grounding is paramount. I’ll look at it–problem is so hot here and those darn monsoons! When I get money, I will put a new 351W in her. The valves were done at 125,000 so has 79,000 since—It burns zero oil. My problems started when I took it to Ammco to overhaul the transmission—Those jokers can’t find their rear end with both hands and a map! —I found a good mechanic who said I had timing chain stretch-he didn’t charge me anything as he changed the timing to match the stretch—What a difference! The car had zero pep–and it took care of a lot of issues----I had previously taken it to Firestone—they screwed things up and when I complained they said leave and never come back! Ha! Live and learn as they say, I spent thousands of dollars there and the mechanic who did a lot of things to it–like complete A/C, drive train, etc–did a great job–but—he left- She is a classic and insulted me calling it an old car! ----- The owner had the personality of a roof shingle! I don’t need people like that in my life at 83 years old-------I’ll keep in touch!
2022 - 1973 = 49 years. Due to Covid complications, 49 year old truck is currently my sole source of transportation. So hoping the old-technology points keep on working … lol …
One thing going in my favor, diagnosing and fixing points a pretty simple job. I did it in the hardware store parking lot, using inexpensive tools I purchased at the hardware store.
Of course, drum brakes all round … lol …
The 351 is a great engine. Relatives had a Galaxy 500 w/ that engine, one day out the middle of Colorado mountain nowhere the water pump failed, barely get to the next very small town, 8 pm, night, winter, snow, cold, gas station closed. Somebody noticed me knocking on gas station door, they called town fix-it guy, he came over, said “good news, it’s a Windsor, my buddy has a Windsor pump, sure, I can fix it, no problem”.
Makes sense. Timing chain slop retards spark timing. Chains don’t actually stretch, instead the chain’s roller pins elongate the holes in the side plate. This sort of wear can’t be totally prevented, but is minimized with frequent oil and filter changes.
I’m a younger geezer. Some years ago I had to take the car for an emissions test, always used the same test shop, b/c if it just needs a little tuning then a re-test, they provide the second test for free. My car needed the second test on this occasion, but tech says “free? no, it’s another $80”. I pointed to the big sign on the side of the shop wall, been there for years, “Second test free”. Tech tears the sign off the wall and throws it in the trash … lol …
Really though points are just fine, thing about them is the work and if they don’t its easy to get them going again. I had a Camaro many years ago and it had points and I tell you what when the timing was set with a fresh set of points and that dwell was dialed in that engine would sing and I mean sing. And that car had reliable, trouble free front drums!
You say the fuel pressure is ok. Does that mean the fuel system is holding and maintaining fuel pressure while the engine is at rest?
Remove the fuel pressure port cap. Since you say the pressure is ok I assume there is a gauge attached. Crank it over a few seconds. Allow it to sit for a while; checking the pressure now and then. If it goes to zero there’s an issue with the check valve in the fuel pump and that will cause a stumble upon startup as it takes a little time to burp the air out of the fuel lines and injectors.
An 89 model also means a possible problematic TFI-IV ignition module. Setting the ignition timing on these is a bit touchy. If the distributor or module has been dinked with the timing MUST be set with the SPOUT connector by the distributor unplugged. Failure to do will cause the timing to be way off.
Sometimes these things will set a trouble code; sometimes not. The TFI problems are heat related and the back of those modules get hotter than a firecracker even with the key on and engine not running.
As for ignition points VW used them well into the 80s on the vans. Personally I don’t have a problem with points. The ones in my antique Harleys are 70 years old and work fine.
Set properly and with distributor cam lube used points should easily go 30k miles. The best electronic system IMO is the old GM HEI which replaced the points. Simple, cheap, and reliable as it can get.
I had a set of points break the fiber block on a Shovelhead Harley on the way back from Sturgis. It was coughing and running horribly. With electronics in NW Nebraska wastelands I would have been up the creek without a paddle. Stopped at a parts store and they had a set of VW points. I also bought a small round file, elongated the adjustment slot, and voila. On my way; and those points were still in there over 2 years later.
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I’ll check that fuel pressure again–I believe for said it should hold for 15 second before slowly dropping------it had shown before 35 pounds—The tolerance should be , as stated by ford, 35–40
would a pump the puts out a full 40 be better? if I cycle the key twice it jumps up to about 40----so does a lot of pressure better for start? I was told that doesn’t matter as long as it is at least 35 pounds-??? can’t find an answer to that anywhere------I’ll keep in touch----I did move the ICM to the fender–got id off the distributor so if on the highway it craps out–it is an easy change.
Sometimes the mounting method on these sorts of gadgets is what provides the ground connection. So be sure to double check by repositioning the part you haven’t affected its grounding. No experience with that part myself, just offering up a guess.
Thanks–sand papered all connections–all is well! only thing I will do, when the weather cools down, is put a motor craft part there instead of an O’ Reiley part!
If a replacement ICM failed right out of the box, usually it wouldn’t work at all, no spark, engine would never start or run. The symptoms you have imo indicate a weak spark. Suggest to ask an experienced shop tech to take a look at the spark right at the tip of a spark plug during cranking. It should look healthy & be blue-ish white colored, and not orange-ish or red.