Missing at low RPM under load sometimes

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Kreechure

New member
Joined
Apr 25, 2022
Messages
13
Reaction score
7
Location
Death Valley, CA
These past few months I've been working on figuring out why.
I replaced everything spark plugs spark plug wires cap rotor vacuum lines everything and a new ignition module which is $95 with tax which I don't think I needed to come to find out because somebody had put a aftermarket plug onto the ignition module that goes on to the distributor and it looked fine I mean all the connectors were secure soldered sealed shrink wrap everything it was a good but then when I unplugged it you know when I was messing with it I noticed that that's when it would die or not start is when I messed with that plug and so I got the looking at it and where they put it together with the little red thing that goes in there where it plugs in the number two plug was just a little bit bent back so it wasn't making a good connection sometimes and that's what the problem has been all these months is that one little thing I took it apart bent it back put it back together and his friend fine ever since so it's like my boss always said keep it simple stupid kiss speaking of kiss, Kiss Army rocks! I've been a life member since I was like 11 years old of the KISS Army
 

Motech

Well-known member
Joined
Jun 21, 2021
Messages
494
Reaction score
575
Location
Santa Cruz, CA:
So is this not a help request then? Just some information?

If so, excellent find, and good information to put out there.
 

Unthrottled

New member
Joined
Jan 12, 2023
Messages
6
Reaction score
5
Location
Grass Valley, CA
These past few months I've been working on figuring out why.
I replaced everything spark plugs spark plug wires cap rotor vacuum lines everything and a new ignition module which is $95 with tax which I don't think I needed to come to find out because somebody had put a aftermarket plug onto the ignition module that goes on to the distributor and it looked fine I mean all the connectors were secure soldered sealed shrink wrap everything it was a good but then when I unplugged it you know when I was messing with it I noticed that that's when it would die or not start is when I messed with that plug and so I got the looking at it and where they put it together with the little red thing that goes in there where it plugs in the number two plug was just a little bit bent back so it wasn't making a good connection sometimes and that's what the problem has been all these months is that one little thing I took it apart bent it back put it back together and his friend fine ever since so it's like my boss always said keep it simple stupid kiss speaking of kiss, Kiss Army rocks! I've been a life member since I was like 11 years old of the KISS Army
Thanks for your post, @Kreechure

Really helpful.

I've had the exact same issue you described on my 1994 XLT, missing, bucking, jerking, at low RPM's under load. Like your problem, my issue is intermittent, but usually happens when I'm going uphill at freeway speed and I back off on the gas a bit dropping the RPM's to 1700-1800.

I don't know if it's my imagination or not but it also seems worse in cold and wet weather.

I've been trying to fix this for years. So far, I've tried all of the same repairs you mentioned plus and a few more, including a new TPS, fuel filter, fuel pump, coil, and more. I've thrown a ton of time and money into wasted repairs, and never fixed the problem.

I'm going to try your fix for sure.

Would love to know what year and model your Bronco is...

Again, thanks!
 
OP
OP
Kreechure

Kreechure

New member
Joined
Apr 25, 2022
Messages
13
Reaction score
7
Location
Death Valley, CA
Thanks for your post, @Kreechure

Really helpful.

I've had the exact same issue you described on my 1994 XLT, missing, bucking, jerking, at low RPM's under load. Like your problem, my issue is intermittent, but usually happens when I'm going uphill at freeway speed and I back off on the gas a bit dropping the RPM's to 1700-1800.

I don't know if it's my imagination or not but it also seems worse in cold and wet weather.

I've been trying to fix this for years. So far, I've tried all of the same repairs you mentioned plus and a few more, including a new TPS, fuel filter, fuel pump, coil, and more. I've thrown a ton of time and money into wasted repairs, and never fixed the problem.

I'm going to try your fix for sure.

Would love to know what year and model your Bronco is...

Again, thanks!
1990 XLT 302 w/ automatic
 
OP
OP
Kreechure

Kreechure

New member
Joined
Apr 25, 2022
Messages
13
Reaction score
7
Location
Death Valley, CA
These past few months I've been working on figuring out why.
I replaced everything spark plugs spark plug wires cap rotor vacuum lines everything and a new ignition module which is $95 with tax which I don't think I needed to come to find out because somebody had put a aftermarket plug onto the ignition module that goes on to the distributor and it looked fine I mean all the connectors were secure soldered sealed shrink wrap everything it was a good but then when I unplugged it you know when I was messing with it I noticed that that's when it would die or not start is when I messed with that plug and so I got the looking at it and where they put it together with the little red thing that goes in there where it plugs in the number two plug was just a little bit bent back so it wasn't making a good connection sometimes and that's what the problem has been all these months is that one little thing I took it apart bent it back put it back together and his friend fine ever since so it's like my boss always said keep it simple stupid kiss speaking of kiss, Kiss Army rocks! I've been a life member since I was like 11 years old of the KISS Army
 
OP
OP
Kreechure

Kreechure

New member
Joined
Apr 25, 2022
Messages
13
Reaction score
7
Location
Death Valley, CA
Okay I thought I had it figured out that plug thing but although that did get it running it did not cure the problem of cutting out at low RPMs under load so I'm back to square one I guess anybody with some insight I'm all ears
 

Motech

Well-known member
Joined
Jun 21, 2021
Messages
494
Reaction score
575
Location
Santa Cruz, CA:
A bit more on your symptom would be helpful. Low RPM is helpful, but "under load" is vague. Like part throttle load? Wide open? Up hills? When launching?Engine cold or warm?

Try running it with EGR vacuum hose disconnected. If better, then too much EGR flow, either faulty valve or too much vacuum applied.

Also, if you're able to perform the On-Demand Running Self-Test, your cause might trip a code that will not appear anywhere else. Could be very helpful.
 

Gibson50

New member
Joined
Jan 25, 2023
Messages
1
Reaction score
2
Location
Asheville, NC
Thanks for your post, @Kreechure

Really helpful.

I've had the exact same issue you described on my 1994 XLT, missing, bucking, jerking, at low RPM's under load. Like your problem, my issue is intermittent, but usually happens when I'm going uphill at freeway speed and I back off on the gas a bit dropping the RPM's to 1700-1800.

I don't know if it's my imagination or not but it also seems worse in cold and wet weather.

I've been trying to fix this for years. So far, I've tried all of the same repairs you mentioned plus and a few more, including a new TPS, fuel filter, fuel pump, coil, and more. I've thrown a ton of time and money into wasted repairs, and never fixed the problem.

I'm going to try your fix for sure.

Would love to know what year and model your Bronco is...

Again, thanks!
I have had your EXACT symptoms for over a year in my 1990 with the 5.8.Finally resolved it by replacing the 3 blown capacitors in the ECM. Open it up and check it out. Hope this helps!
 
OP
OP
Kreechure

Kreechure

New member
Joined
Apr 25, 2022
Messages
13
Reaction score
7
Location
Death Valley, CA
These past few months I've been working on figuring out why.
I replaced everything spark plugs spark plug wires cap rotor vacuum lines everything and a new ignition module which is $95 with tax which I don't think I needed to come to find out because somebody had put a aftermarket plug onto the ignition module that goes on to the distributor and it looked fine I mean all the connectors were secure soldered sealed shrink wrap everything it was a good but then when I unplugged it you know when I was messing with it I noticed that that's when it would die or not start is when I messed with that plug and so I got the looking at it and where they put it together with the little red thing that goes in there where it plugs in the number two plug was just a little bit bent back so it wasn't making a good connection sometimes and that's what the problem has been all these months is that one little thing I took it apart bent it back put it back together and his friend fine ever since so it's like my boss always said keep it simple stupid kiss speaking of kiss, Kiss Army rocks! I've been a life member since I was like 11 years old of the KISS Army
Nope! I thought I had it but it's doing it again. Since my last post I did install a new MAP sensor and that seemed to help but, it wasn't long before she went back to her old shenanigans. Except now on top of the missing at low idle it now stalls occasionally. Usually in the busiest of intersections.
 

miesk5

96 Bronco 5.0
Staff member
Moderator
Joined
Oct 18, 2005
Messages
9,071
Reaction score
1,018
Location
Floating in the Pacific
Yo Kreechure,
As member Motech advised,
Try a Self Test for Diagnostic Trouble Codes by my pal, BroncoJoe19 @ Code Reader.....

PCM stores the Self-Test program in permanent memory. When activated, Self-Test checks the EEC system by testing memory integrity and processing capability, and verifies that various sensors and actuators are connected and operating properly..
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test. Run it around to heat the engine up and shift thru all gears including Reverse. Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual and; release clutch. Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First. Post Code(s) here according to KOEO and KOER.

A helper can assist you by counting the codes. Some use their smart phones to record them.

BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS⚠

Or ask local mom and dad parts stores if they will test it for you.

Or purchase a coder reader such as Equus 3145 Innova OBD I Code Reader for Ford EEC IV Engines at Walmart & most parts stores.
 

Motech

Well-known member
Joined
Jun 21, 2021
Messages
494
Reaction score
575
Location
Santa Cruz, CA:
she went back to her old shenanigans. Except now on top of the missing at low idle it now stalls occasionally.

Funny, I just now finished diagnosing a similar problem, 1988 5.0 F150.


Problem was voltage spikes at closed throttle on the TPS signal. The connector was not secured on the throttle body bracket, and instead was jammed down against the back of the alternator wrapped up in the voltage regulator wires and cylinders one and two spark plug wires. These were causing a bunch of voltage spikes on the signal with erratic, low idle and stalling. Simply moving the connector back up to the bracket and securing it there fixed the problem.
 

paul rondelli

Active member
Joined
Mar 18, 2021
Messages
132
Reaction score
124
Location
Atlanta
The wonderful world of owning a 30-year-old piece of equipment.

Sounds like an electrical issue. You are already all over that with the TPS and coil.

The electrical components are not made to last 30 years ... so do not look at this as throwing away good money. Look at it was wear items that would need to be replaced anyway. Keep of record of when you replaced them ... so you can see if they go bad.

OBD1 is not going to give you much information..... and chasing down electrical issues is almost as fun as a root canal.


Could be a plug wire going bad ..... distributor .... ECU ..... ICM.... ground wire.... shorted wire .... yadda yadda yadda

Your vacuum lines are probably all original ... along with most of the emissions stuff.

If this were me .... I would try to rule out certain systems first

1) test the fuel pressure to ensure no issues with fuel delivery ... filter clogged/ Line jacked up
2) maybe install a cheap boost/vacuum gage to allow you to see what is happening to that system in real time.

Once you can positively rule those out ... then it is multimeter time ... and a few cases a beer. Start with any component close to a heat source. Anything electrical will fail sooner if you just add excessive heat.

My buddy bought a used Lexus. They make those things almost airtight. You have insulation under the hood ... and even the wheel well have insulated material. It sure keeps the engine noise down ..... but I don't see any where for the heat to go? Keeping all the heat inside the engine bay seem like a good recipe for electrical component failure.
 

Tiha

Well-known member
Staff member
Moderator
Joined
Jul 22, 2020
Messages
969
Reaction score
1,010
Location
Midwest
Usually in the busiest of intersections.
Does this only happen when hot? Or will do it cold as well?

Had one doing something similar, shop swore it was a bad injector, turns out it was a weak fuel pump. But I am sure it needed injectors anyway.
 

Motech

Well-known member
Joined
Jun 21, 2021
Messages
494
Reaction score
575
Location
Santa Cruz, CA:
on top of the missing at low idle it now stalls occasionally. Usually in the busiest of intersections.

I want you to try two things here:

1. When symptom is occuring consistently, disconnect your SPOUT shorting bar. This is the timing connector near your ignition control module connector. Unplug it while idling. If symptom improves, you probably have a PIP sensor begining to fail. (Pickup sensor inside distributor)
A new sensor needed, but easier and cheaper to plop in a replacement distributor.

2. Warm idle, preferably without symptoms, disconnect two wire Idle Air Bypass Valve (aka IAC valve) on driver side of throttle body. If engine stalls, your minimum intake air rate is too low.

To fix this, first thoroughly clean throttle bores, reconnect IAC, fire it up, clear it's throat and try it again. If it still stalls when you unplug IAC, then access the little throttle stop ***** and lock nut and with IAC disconnected, increase closed throttle angle until you achieve 500 idle RPM with IAC disconnected.
This is your "Minimum Air Rate".

Note: this will probably require multiple restarts, as it will continue to stall, and you'll have to restart with IAC reconnected and check it again with each adjustment.

Once 500 RPM Min Air Rate is achieved, plug it all back in and disconnect battery for 15 minutes to erase memory so computer can readapt new TPS value and reestablish new idle controls.

And don't be alarmed with your surging idle after that, especially during cold start. It is common for these Ford systems to struggle like this the first couple three cold starts during relearn after memory erase. Will progressively get better, and likely be gone after the third warmup.

I can't even count how many small block EEC IV truck engines I've solved poor idle/stalling issues this way over the last 30 years. Heck, three this June alone!
 

Staff online

Members online

Latest posts

Forum statistics

Threads
22,509
Messages
135,880
Members
25,108
Latest member
Utahstroke
Top