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Discussion Starter · #1 · (Edited)
Hey everyone. Have an issue when I am at a constant throttle position, speed or gear does not matter, where the engine stutters like it’s miss firing a cylinder. Starts great, idles great, WOT is great, only have the issue when throttle position is constant (actual position varies depending on speed/gear) and not under a load. Example would be if going through the neighborhood in 3rd at 1/4 throttle, main road in 3rd at 1/2 throttle, main road 4th 1/4 or 1/2 throttle, or highway in 5th 1/4 or 1/2 throttle I experience the same issue. I have zero codes other than the 11/10 and no CEL.

Items replaced and/or tested-
6 liter ignition upgrade (plugs gapped at 50, wires, cap, rotor, coil, timing at 12.5), new MAP (fixed previous continuous code), new temp sensor, new fuel filter and regulator (pressure is now within spec). New HEGO and fixed the ground going to the PCM. New EGR/EVP/vacuum solenoid (fixed previous continuous code) solenoid wires have been tested. TPS and IAC tests good. All vacuum lines have been verified (not blocked or leaking). Upper plenum gasket seem good when using the good ol starter fluid test (even under the plenum on passenger side).

What would cause this? If I had a code I could troubleshoot further but I’m at a loss.

Any help or suggestions is greatly appreciated!
 

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Every time I've run into this it was EGR related, specifically a vacuum leak in the EGR valve itself. The EGR valve on these, as you may know, consists of the valve itself along with an EGR valve position sensor mounted on top of the EGR valve. What happens is that when the computer enters lean/cruise mode, it'll lean out the mixture. If there is a vacuum leak present, it'll be too lean of a mixture and the truck will develop the symptoms you describe.

Since you've already replaced the EGR valve it's not likely that the EGR diaphragm has developed a leak, so I would start looking elsewhere in the EGR vacuum chain. Could be leaking in the TAD/TAB sensor area.

Just for grins, why don't you disconnect the vacuum line running to the EGR valve and plugging it off with a golf tee or something. Drive the truck and see what happens.
 

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Yo AnthonySunderland,
Welcome!
Table 9:
180917


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.

Here are the 1989 Ford Bronco EVTM, Emissions (yellowish/red book cover) & Pre-Delivery Manuals, Partial via mrnewland1 in Google Drive @
1989 Service manual - Google Drive
Slow scrolling, so download for faster viewing and to see the table of contents, the search feature, etc.

Haynes Red Manual for 80-95 Bronco & F Series @ Hanes guide 80-96 bko f series.pdf found by BroncMom

1989 Ford Bronco Dealer Brochure

1989 Bronco Lubricant Specifications by Ford via Gary

For any Bronco questions, it's better to post each seperately in Noobie Bronco Tech Questions. Flame free zone. This will get more attention and you can build up your post count to get into other sections such as Bronco and Ford Parts/Accessories (50 posts required to participate due to scammers who preyed on our members).

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Discussion Starter · #4 ·
Every time I've run into this it was EGR related, specifically a vacuum leak in the EGR valve itself. The EGR valve on these, as you may know, consists of the valve itself along with an EGR valve position sensor mounted on top of the EGR valve. What happens is that when the computer enters lean/cruise mode, it'll lean out the mixture. If there is a vacuum leak present, it'll be too lean of a mixture and the truck will develop the symptoms you describe.

Since you've already replaced the EGR valve it's not likely that the EGR diaphragm has developed a leak, so I would start looking elsewhere in the EGR vacuum chain. Could be leaking in the TAD/TAB sensor area.

Just for grins, why don't you disconnect the vacuum line running to the EGR valve and plugging it off with a golf tee or something. Drive the truck and see what happens.
Thanks for the tip flomaster! I disconnected and plugged the vacuum line running to the EGR and there was no change. The EVP sensor and vacuum solenoid have been replaced and do not throw any codes. All vacuum lines test good for no leaks or blocks. Electrical from the solenoid to the PCM has been verified as well. I though this was all EGR related as well, that why I did the replacements and tested all vacuum/electrical. The troubleshooting continues....
 

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Discussion Starter · #5 ·
Thanks for the tip flomaster! I disconnected and plugged the vacuum line running to the EGR and there was no change. The EVP sensor and vacuum solenoid have been replaced and do not throw any codes. All vacuum lines test good for no leaks or blocks. Electrical from the solenoid to the PCM has been verified as well. I though this was all EGR related as well, that why I did the replacements and tested all vacuum/electrical. The troubleshooting continues....
Update- Turns out it was either the PIP or the control module in the distributor. Replaced the distributor with a new one (remand supposedly have possible magnetic issues) and it drives awesome now!
 

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Update- Turns out it was either the PIP or the control module in the distributor. Replaced the distributor with a new one (remand supposedly have possible magnetic issues) and it drives awesome now!
I'm having the same issue. But I've changed my distributor about 3 months ago or so. I put a cardone remanufactured one in. It has a lifetime warranty. Now I'm wondering if the new one is bad. I've also changed fuel pump around the same time. Done plugs, wires, cap, rotor, icm, cps, tps, iacv, vacuum lines, cleaned throttle body, new air filter, thermostat, ignition switch, coil, fuel filter about a year ago, fuel pump relay...I'm at a loss as to what it can be. It started just cutting out every now and then seems like after it got warmed up and drove for about 30 minutes. Now it's getting worse. Not usually at idle only when accelerating. It'll jerk and buck a few times then back to normal. It's not constant.
 

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Yo Jessi,
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19 @ Code Reader
EEC AKA PCM, computer 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 EEC will tell you what it found out by testing your sensors, and also any stored information it saved from anything that went wrong during the last 40 trips.
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 & 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 & 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 1 Code Reader for Ford EEC IV Engines at Walmart & most parts stores.

For No applicable Diagnostic Trouble Codes;
See Table 8;
Font Parallel Pattern Paper Rectangle

QUICK TEST IS TEST FOR DIAGNOSTIC TROUBLE CODEmoS
Iggie Scope for Now
ISC is
Rectangle Product Font Line Screenshot

See my Vacuum leak test in my post #11 @ Help with dtc codes and idle
 
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