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1990 5.0 XLT, E40D
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Discussion Starter · #1 ·
Hi All,

I have been trying to get the engine running as close to perfect as I can. Even rebuilding the engine in 2004 I didn't replace a lot of sensors then. Not a lot of miles on the engine still somewhere between 40k and 60k. I finally got it back this summer after sitting at my parents for years. About 3 or 4 years ago a family friend was fresh out of the airforce as a mechanic so we through some cash his way to get the bronco running. He did your typical tune up, new plugs, wires, cap, rotor.

Revving issues at idle have been an issue. So been searching the forums and youtube pretty hard, if there was something that might need to be replaced i would replace it (since the originals are over 400k miles)

First took it to a local shop that i paid in beer for labor (I own a brewery, did a tune up and got everything running pretty well, just the high rev issue was tough to solve. Flushed the radiator checked the plugs, cap & rotor and all were in good shape.

Trying to fix the rev issue at idle:

Things I've replaced so far (one by one to figure out the cure):
  • all vacuum lines with the silicon per Replace Plastic Vacuum Hoses with Rubber
  • IAC valve (motorcraft CX1828)
  • PCV and TAB
  • intake manifold gasket (was leaking per shop)
  • EGR Valve+Sensor+Connector (cheap aftermarket from RockAuto)
  • MAP Sensor (motorcraft CX2403)
  • ICM Module (solved the high rev issue in park at idle) (motorcraft DY-1284)

I was still having trouble after warm up when stopped at a light, the ICM replacement definitely helped but there would still be a slight stumble and a little serge. So i continued my quest:

  • Replaced the TPS sensor (motorcraft CX1228)
I started noticing i was spraying a black tar soot out of the exhaust, must have been happening for a while cause the concrete was stained by my exhaust. So i looked into it and from what i gathered it the most common culprit was the Fuel Pressure Regulator, so I just replaced it. Now I'm having the hunting and surging issue with the engine again, it actually is stalling on me. I purchased Standard Motor Products Fuel Injection Pressure Regulator from Rockauto, wasn't the cheapest, but was $21.79 vs Motorcrafts $92.79 price.

I know when the mechanic did the flush he said my thermostat was working fine, so he didn't replace it. I have a hunch that I may have misread something during my rebuild in 2004 that i could use a 160 degree thermostat to get more power, can't remember if that actually happened. I now know from reading through the forums that is a bad idea. I've been avoiding the labor of getting to the thermostat, but i think i'm at that point now.

Here is a photo of the exhaust, after my venting. If anyone has suggestions I'd be glad to hear it.

172062
 

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Hi All,

I have been trying to get the engine running as close to perfect as I can. Even rebuilding the engine in 2004 I didn't replace a lot of sensors then. Not a lot of miles on the engine still somewhere between 40k and 60k. I finally got it back this summer after sitting at my parents for years. About 3 or 4 years ago a family friend was fresh out of the airforce as a mechanic so we through some cash his way to get the bronco running. He did your typical tune up, new plugs, wires, cap, rotor.

Revving issues at idle have been an issue. So been searching the forums and youtube pretty hard, if there was something that might need to be replaced i would replace it (since the originals are over 400k miles)

First took it to a local shop that i paid in beer for labor (I own a brewery, did a tune up and got everything running pretty well, just the high rev issue was tough to solve. Flushed the radiator checked the plugs, cap & rotor and all were in good shape.

Trying to fix the rev issue at idle:

Things I've replaced so far (one by one to figure out the cure):
  • all vacuum lines with the silicon per Replace Plastic Vacuum Hoses with Rubber
  • IAC valve (motorcraft CX1828)
  • PCV and TAB
  • intake manifold gasket (was leaking per shop)
  • EGR Valve+Sensor+Connector (cheap aftermarket from RockAuto)
  • MAP Sensor (motorcraft CX2403)
  • ICM Module (solved the high rev issue in park at idle) (motorcraft DY-1284)

I was still having trouble after warm up when stopped at a light, the ICM replacement definitely helped but there would still be a slight stumble and a little serge. So i continued my quest:

  • Replaced the TPS sensor (motorcraft CX1228)
I started noticing i was spraying a black tar soot out of the exhaust, must have been happening for a while cause the concrete was stained by my exhaust. So i looked into it and from what i gathered it the most common culprit was the Fuel Pressure Regulator, so I just replaced it. Now I'm having the hunting and surging issue with the engine again, it actually is stalling on me. I purchased Standard Motor Products Fuel Injection Pressure Regulator from Rockauto, wasn't the cheapest, but was $21.79 vs Motorcrafts $92.79 price.

I know when the mechanic did the flush he said my thermostat was working fine, so he didn't replace it. I have a hunch that I may have misread something during my rebuild in 2004 that i could use a 160 degree thermostat to get more power, can't remember if that actually happened. I now know from reading through the forums that is a bad idea. I've been avoiding the labor of getting to the thermostat, but i think i'm at that point now.

Here is a photo of the exhaust, after my venting. If anyone has suggestions I'd be glad to hear it.

View attachment 172062
Thermostat take a whole 10 seconds to replace tbh its two bolts. About the rest, do you have a better explanation on what the issue is? Not sure clear


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1990 5.0 XLT, E40D
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49 Posts
Discussion Starter · #3 ·
I was kind of venting. lol I have been trying to get rid of an idle surge. I got it almost fixed except for when I'm stopped at a light. It idles exactly where it is supposed to now, but maybe after 10 seconds at a stop light it starts to stumble then have to fix itself. Wondering after all the stuff i replaced what left if have to do? I am thinking verify the timing, and maybe do the timing bump with a new cap and rotor via ignition upgrade and timing bump (no 56K)

but after replacing the Fuel Pressure Regulator to get rid of the black exhaust, the rough idle got a lot worse and is stalling at stop lights. I did forget to add i replaced the sending unit and pump 3 months ago as well.

So its kind of a 2 parter, 1 is about the idle issue that was almost resolved before the FPR, 2 is the black exhaust and if its not the FPR (which i guess can still be the issue, since my engine got worse after replacing it) what else could cause the issue?
 

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I was kind of venting. lol I have been trying to get rid of an idle surge. I got it almost fixed except for when I'm stopped at a light. It idles exactly where it is supposed to now, but maybe after 10 seconds at a stop light it starts to stumble then have to fix itself. Wondering after all the stuff i replaced what left if have to do? I am thinking verify the timing, and maybe do the timing bump with a new cap and rotor via ignition upgrade and timing bump (no 56K)

but after replacing the Fuel Pressure Regulator to get rid of the black exhaust, the rough idle got a lot worse and is stalling at stop lights. I did forget to add i replaced the sending unit and pump 3 months ago as well.

So its kind of a 2 parter, 1 is about the idle issue that was almost resolved before the FPR, 2 is the black exhaust and if its not the FPR (which i guess can still be the issue, since my engine got worse after replacing it) what else could cause the issue?
The idling sounds like a vacuum issue to me? Did you check your lines to see if some are cracked?


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Yo 90.CaliBronco,
Surge:
172082


One way to do a quick check for a vacuum leak is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
See more in my Vacuum leak test @ Help with dtc codes and idle
When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

Black Smoke: Black exhaust smoke is an indication of rich fuel condition. These are possible causes:

Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.

Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.

Fuel Return: A restricted fuel return line will cause a rich fuel condition.
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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I had a very similar thing, super rich with gas spitting out black wet nasty shit just like this. I threw part after part at it & got nowhere, then I broke down & spent $29.99 at autozone on a code reader & it said Air intake Temp sensor. Other things can cause this too, so let the codes lead your spending instead of guessing.

I had replaced every sensor a few months earlier when I bought the truck, just for good measure, so I didn't think it would be a sensor but because of the code, I measured the resistance on the Air Intake Temp sensor & sure enough, it was 1.0, meaning it was shorted out.

I still had the old one still & measured the resistance on it at 0.34 ohms so I put it in & it immediately ran fine, but I did order a new one as well.

After running so rich, I knew to check my oil & sure enough it was way over the full line, saturated with gas, so be sure to change your oil if it is full of fuel like mine was.

Here was my post on that, see post #9

The one that went bad was a $12 Walker sensor with a 90 day warranty. I replaced it with a $15 Delphi with a 1 year warranty. I could not find a Motorcraft available.
 

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1990 5.0 XLT, E40D
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Discussion Starter · #8 ·
I'm going to run codes today. Keep you posted.
 

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Discussion Starter · #9 ·
Ran codes, only one received was during the KOER test, code 21 coolant temp sensor or ect out of range. Going to make the assumption it is the coolant temp not the ECT since it would have been discovered during the KOEO test too
 

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Coolant temperature sensor or Engine Coolant Temperature (ECT) are the same thing.

Ensure the engine was fully up to temperature before running the KOER tests. I believe somewhere north of 165F is required.
 
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Discussion Starter · #11 ·
Coolant temperature sensor or Engine Coolant Temperature (ECT) are the same thing.

Ensure the engine was fully up to temperature before running the KOER tests. I believe somewhere north of 165F is required.
oh duh i was thinking ECM. ya i drove ghe bronco around town for 20 minutes so should have been up to temp. ill replace the thermostat then see what happens.
 

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Also measure the ECT output or resistance.
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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oh duh i was thinking ECM. ya i drove ghe bronco around town for 20 minutes so should have been up to temp. ill replace the thermostat then see what happens.
Just to clarify your thermostat comment.
A thermostat is a thermostat, like on the left & it opens via spring pressure when the coolant gets warm. This is not your problem.

On the right is engine coolant temp sensor & it screws into the intake and has a plug that sends a signal to the computer, that tells it the how warm the engine is, so it can adjust the fuel ratio accordingly. That is what you want to replace. I would also pick up an air intake temp sensor, just because they are cheap & thats what was wrong with mine when I had the same issue.
172434
 

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Discussion Starter · #14 ·
Yeah that whole piece looks pretty bad so i may just replace it with the sensor. i was talking about replacing the thermostat cause per my OG post it may be a 165 stat instead of the 195 stock. just cant remember.
 

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When I got my Bronco, I replaced all the sensors just to start with a clean slate. I did learn not to buy cheap ones, cuz the $8 Walker air temp sensor failed just after its 90 day warranty expired. I replaced it with a Delphi, which was only $12, but had a 1 year warranty.
 

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Discussion Starter · #16 ·
Timing was off, did the sixlitre tuneup. gapped new plugs to 0.055 and timed to 13*, runs better than ever. temp still reading low even though sensor sender and gauge tested fine. so im going to replace the t-stat
 

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Glad to hear it's running good again, but the question is, how did it go from running good, to running bad with the timing was off. Did someone mess with the timing?

Then I thought the spec on timing was supposed to be 10° with the Sprout connector disconnected. Not an expert on the newer trucks, maybe someone can chime in.
 

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Discussion Starter · #18 ·
so it was never running properly, it had minor idle issues so i replaced sensors one by one and it seemed to be getting better and better but when i replaced the icm and tps then it started doing worse for some reason. no codes except the temp issue so decided to check the timing and it was off.

i think it was when i replaced the icm cause you have to take the distributor out to replace it. i must of put it back incorrectly. but i received a good xmas gift from the in-laws and used it to purchase the tune up kit: autolite plugs gapped to 0.055, 8mm ford racing wires, motorcraft coil, new distro cap and rotor. bumped the timing to 13° per the sixlitre tuneup guide. heres the link

you are correct stock timing is 10°
 

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Ahhh gotcha, never read the 6 liter tune up.
I always hear it mentioned, but my 86 had a new crate 302 in it when I bought it, and like you, I replaced all the sensors & haven't had any problems to deem digging any further yet. I should thrown timing light on it one of these days. I go with the, its not broke, dont fix it methodology!

Edit: just read the "6 Liter tune" not much to it, makes sense.
 
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