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Hoping you guys have a quick and easy fix...


Detroiter

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Greetings all. I wonder if you all might be able to help me diagnose couple of issues that I believe are related. The truck is an '88 Bronco II with a 2.9 and an automatic. It's relatively new to me, so I'm not yet all that familiar with it.

Problem one: The truck starts right up when it's (Detroit in winter) cold, and instantly settles into a nice idle. If left sitting it'll idle happily until it starts to warm, at which point it surges badly for thirty seconds or so, and then settles back into a consistent idle. If I drive away without letting it warm it goes through a similar phase, though when moving down the road it feels like a really bad miss, and the resultant loss of power.
Problem two: When warm it is reluctant to start. By that I mean it fires right up, but quits. Almost as though it's out of gas and I've spayed into it just enough ether for it to catch. It'll do this once, twice, have a dozen times, but in the end fires up as though all is well. It hasn't up to this point left me stranded, but I can't say that I'd trust it in an emergency...

Logic is telling me it's a sensor of some sort, so I figured I'd ask the question here in case it's a previously seen scenario.

Many thanks,
E
 


Rock Auto 5% Discount Code: 7FA902352B4C01: April 5th, 2021

kimcrwbr1

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Go to the tech library and read up on pulling the codes. You can try disconnecting the battery and short the pos battery cable to ground. That resets the computer to new values. Then see how it runs for about 20 minutes. You can pull the codes with a test light or analog volt meter the tech library will explain what you need to do. It could be multiple issues so erase the codes and retest after each repair. Always address the lowest number first and retest if you clean or replace a component. Erase the stored codes and reset the computer by disconnecting the battery and shorting the + cable to ground. If you have a check engine light you just need to jumper the test connector to pull the codes. The OBD connector is under the hood by the battery...
 

Detroiter

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Thank you, kim. I'm on it.
 

kimcrwbr1

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It is under EEC-IV diagnostics if your using a light or volt meter it is easier to have someone write down the codes as you count. A code reader you can count the beeps...
 

kimcrwbr1

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ericbphoto

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Reading codes is excellent. I wouldn’t be surprised if it points you toward the ECT sensor. That us the 2-wire temperature sensor near the thermostat housing. It tells the ecu when the engine is warmed up. At that time, the ecu controls the engine differently.
 

Detroiter

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Frankly, I haven't had a chance to get struck into it. It proved a weekend busy keeping the girlfriend happy.... And my daily driver is on the hoist for an oil cooler gasket replacement and a couple of new tires...
I'll tackle the Bronco as soon as I can, and will let you know how it goes.
 

JerrySab

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So, I'm super inexperienced and invite you to please take this with much salt. This is my first rodeo, learning through failure.. but we have same year and engine soooo..

You might confirm throttle position sensor is clean and working correctly; you might also test the idle air controller and confirm it's operating within intended values.

I had similar stalling issues, where the truck quit during idle once warm. There was no smoking gun, but came down to a combination of vacuum leaks at airbox and throttle plate, intermittent failure at TPS, IAC, ICM, poorly gapped plugs, over-advanced timing, poor exhaust pressure due to hollowed out cat.. very rough idle is almost entirely smooth, no longer dealing with stalls.
 

Detroiter

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Thanks for the replies, fellas. I followed initial advice, and read through the the tech articles. Then because I'm lazy and counting flashing lights seemed arduous and like something I could easily screw up, I bought a code scanner... After reading through the destructions, etc., I plugged it all in. The first thing I did was clear the saved codes. This truck is new to me, so as far as I knew anything saved could have been from 25 years ago. Then I ran the tests.
I got no Key On Engine Off faults.
I did, however, get a Key On Engine Running Slow Code fault: 41 H2O system lean bank one
I got the same fault as a KOER Fast Code in addition to: 77 WOT not detected during self test
At that point I pretty much ran out of time for the day. Many projects, and this one is not high priority...
I figure I'll drive it a little bit, recheck, and see if something else crops up.

More to follow.
 

vagabond80

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Thanks for the replies, fellas. I followed initial advice, and read through the the tech articles. Then because I'm lazy and counting flashing lights seemed arduous and like something I could easily screw up, I bought a code scanner... After reading through the destructions, etc., I plugged it all in. The first thing I did was clear the saved codes. This truck is new to me, so as far as I knew anything saved could have been from 25 years ago. Then I ran the tests.
I got no Key On Engine Off faults.
I did, however, get a Key On Engine Running Slow Code fault: 41 H2O system lean bank one
I got the same fault as a KOER Fast Code in addition to: 77 WOT not detected during self test
At that point I pretty much ran out of time for the day. Many projects, and this one is not high priority...
I figure I'll drive it a little bit, recheck, and see if something else crops up.

More to follow.
We're all having this at the same time... funny.
During the KOER you need to put the pedal to the floor for half a second (or maybe only 25% technically, not sure but I'm told just floor it) and that's your WOT situation.
I have a 41 after driving for a while, not even getting save in memory now, but the truck seems to run just fine. bit frustrating.
o2 sensor codes really are like having a fever: only a common symptom of a plethora of potential problems.
Since your symptoms are more acute, hopefully it can get figured out quickly and easily. as others have said, testing the temp-related circuits first makes sense in your case.
Other things to do would be check all the grounds, especially for o2, and check the blue capacitors in the ECU for damage/leaks
 


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