No power on acceleration and erratic idle on startup

[JimC25]

My ‘89 is coming along, but it has erratic idle at startup, which evens out after 5-10 seconds if it doesn’t stall. Also, it has no power. It has the 5.0 with AOD transmission. The engine was recently rebuilt and I am about 400 miles into the break-in. So far I’ve replaced the O2 sensor, coolant temp sensor, idle air control valve, tps and map sensor. I also replaced the coffee can vacuum reservoir on the passenger side. I checked for vacuum leaks using carb cleaner and haven’t found any. Thinking it may be the ECM at this point, but interested in any thoughts on what I’m missing. Also only getting code for power steering pressure switch and knock sensor, 25 and 52. Thanks!

 

[miesk5]

Yo Jim,
Here are some possible perpetrators for it's issues and NO Related Diagnostic Trouble Codes SUCH AS WHAT YOU FOUND;
IAC
TABLE 12
TABLE 6
& See my Vacuum leak test in post #11 includes jowens1126 HVAC Control Panel info @ https://www.fullsizebronco.com/threads/help-with-dtc-codes-and-idle.206824/
Tip; 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.
Al

 

[JimC25]

Thanks Miesk! I'll start chasing those and report back.

 

[JimC25]

Latest update is I started with the EGR valve. Tested the EGR Solenoid and the Sensor and they both tested good, so replaced the EGR Valve. Unfortunately, didn't fix the problem. I'll probably keep checking for vacuum leaks or check the EVAP system next as I work through the list of possibles. Thanks again Miesk for the list! I can't attach a video, so here's some more details about what it is doing. On cold startup, it usually starts after a few seconds and will go to about 1400 rpm's for about 8 seconds, then drop to about 200 to 300 for a second or two and either die or jump back up to around 1700 rpms, From there, it will hover there for a few seconds, then gradually come down to around 1200, back up to around 1500 a few times until it warms and then stay steady around 1400. Also, pickup seems a little better, but still feels kind of sluggish on takeoff. Let me know if that gives any better clues. Thanks!

 

[JimC25]

Checked fuel pressure last night and got 30 at the rail at idle. Increased rpm's and it briefly went up to about 34, then dropped to 29-30, where it stayed. The manual states it should have between 30-45 psi at the rail at idle. Could being on the low end cause the idle to surge when cold and it to hesitate or drag while driving? I tested the fuel pressure regulator and it did shoot up to 41 when I disconnected the vacuum hose and dropped down to 30 when I reconnected it, so I think it is good. Considering changing the fuel filter. I changed it when I started the restoration about a year and a half ago, but thinking it may have clogged over time, since the truck had been sitting for some years before I started digging into it and I never flushed the tank.

 

[miesk5]

Yo Jim,
PRESSURE IS IN RANGE.

ENGINE RUNNING​

​

28-45 PSI​

FDS4 CHECK PRESSURE REGULATOR DIAPHRAGM CONDITION​

• Key off.
• Connect Fuel Pressure Test Kit at Schrader fitting on rail. Observe Warning Instructions to avoid fuel spillage and injury.
• Start engine and run for 10 seconds.
• Stop engine and wait 10 seconds.
• Start engine and run for 10 seconds.
• Stop engine and remove vacuum hose from pressure regulator.
• Examine vacuum port in the pressure regulator for evidence of fuel leakage through the diaphragm.

Is vacuum port free of any fuel?

Yes	No
GO to Group 10 of the Service Manual for leak test.	REPLACE pressure regulator and RERUN test

Read more @ http://www.diesel-dave.com/vehic/manual/vra/leftside=vras9al.htm&rightside=vras9ar.htm

 

[JimC25]

Thanks, I'll check that off of the list.

 

[JimC25]

Not sure if I did this right, but here goes. Still checking for vacuum leaks. With engine off, I blew smoke into the intake from one of the vacuum hoses coming from the intake tree. Hoping to see if any smoke comes out anywhere to identify a possible leak. Smoke came out of the EGR valve vents. Thinking the EGR valve should be closed unless vacuum has pulled it open, so this may be part of my issue. Am I thinking correctly on this? Thanks!

 

[Tiha]

Yes, it should be closed.

For testing I usually loosed the EGR and stick a quarter, or cut a piece of tin or something and slip under it, tighten back down.
Doesn't have to be perfect, just needs to mostly block the EGR and elminate that as a problem during trouble shooting.

 

[miesk5]

Not sure if I did this right, but here goes. Still checking for vacuum leaks. With engine off, I blew smoke into the intake from one of the vacuum hoses coming from the intake tree. Hoping to see if any smoke comes out anywhere to identify a possible leak. Smoke came out of the EGR valve vents. Thinking the EGR valve should be closed unless vacuum has pulled it open, so this may be part of my issue. Am I thinking correctly on this? Thanks!

Yo Jim,
If EGR valve is stuck open, it will essentially cause a vacuum leak, leading to inefficient combustion, rough idling, hesitation & sometimes, stalling.
jowens1126 has an easy test, "all you really need is a piece of vacuum tube. remove egr valve, attach vacuum line, **** on the open end, look at the bottom of the egr valve to make sure the pintle moves and hold vacuum on the line to make sure it doesnt leak down and close. thats pretty much all you need to do there. You can clean the insides up with brake kleen to get all the gunk out of it. It will make it move alot easier."

A quick check to determine if this passage is open can be made as follows: With the engine idling, push the EGR valve diaphragm open (using a screwdriver if the engine is hot). A quick check to determine if this passage is open can be made as follows: With the engine idling,push the EGR valve diaphragm open (using a screwdriver if the engine is hot). A noticeable change in idle speed or engine stalling is an indication the EGR passage is open. Replacement of the EGR valve should be considered at this point. This same carbon accumulation can plug the valve's passages preventing proper operation.CAUTION: EGR valves can get very hot!.

 

[JimC25]

Thanks guys! Ended up changing the EGR, now I’m getting code 32 - EGR Presssure Feedback Fault, so I’ve got some more testing to do.

Also, out of curiosity, I pulled my ECM to give it a look. Not sure exactly what i’m looking for, but are the dark spots around some of the components something to be concerned about? I read where some of the components leak over time and cause issues.

 

[Tiha]

Wait for a second opinion but it looks like a couple leaky capacitors in that ECM

 

[miesk5]

Yo Jim,
I see a leaky Capacitor too, as well as a burn mark on something else ( poor vision here) .

Here are some PCM KILLER perpetrators and other causes:
Smell around the PCM. If it smells like dead fish, it's bad.
Look at these PCM printed circuit board burn marks around leaking capacitors, resistors.
View attachment 182797
For example, see Old leaky capacitors in swapped EEC and no more codes by jowens1126

Water damage from cowl leaks, ESPECIALLY if you you have wet carpet or mat near driver kick panel; or on PCM Connector due to a bad hood seal near cowl panel, viewable with hood up.
Corrosion or damage due to moisture is one of the main reasons for failure. Corrosion can enter through the wiring harness and moisture can enter by a failure in the seals in the PCM itself. This happens over a period of time (5 to 10 years) due to exposure to the elements.
The alternator could be generating an AC voltage spike due to bad diode(s) or supply Voltage
View attachment 182796
Overloads.

Thermal stress due to excessive heat and excessive vibration that causes sensitive parts to fail.
Bronco was jump started on reverse polarity.
Connector pin damage or corrosion,
Other internals:
broken tracks,
cold solder joints,
short circuit,
thermal stress due to excessive heat and excessive vibration that causes sensitive parts to fail,
Overheated PC,.
Bad Intel 8061 chip or bad Intel 8361 memory chip,
Bad Internal Voltage Regulator, see Wayback Machine by Fireguy50 (Ryan M)
●
DTC 32
KOEO & KOER EVP circuit below minimum voltage of 0.24 volts.
Here is DTC 31, 32. 33. 34. 35. 38 or 84; EGR Valve Position (EVP) Sensor & EGR Vacuum Regulator Solenoid (EVR) Testing by Ford
Some perpetrators are:
Vacuum leak, damaged EGR Valve, etc.

And just in case:
Jowens has an easier EGR test, "all you really need is a piece of vacuum tube. remove egr valve, attach vacuum line, **** on the open end, look at the bottom of the egr valve to make sure the pintle moves and hold vacuum on the line to make sure it doesnt leak down and close. thats pretty much all you need to do there. You can clean the insides up with brake kleen to get all the gunk out of it. It will make it move alot easier."

Next up to bat is EGR Valve and EGR Position (EVP) Sensor Testing & Replacement @ EGR Valve Position (EVP) Sensor Testing & Replacement
by Seattle FSB

AND;

 

[JimC25]

Thanks guys! Think I will look for another ECM and will also run the tests on the EGR and EVR above. Has anyone had any luck with the rebuilt ECM's from the parts stores or would you go to a specialty store instead? I found one specialty store in town (Houston) that says they have one on the shelf which is a direct replacement for the one I have, but about $60 to $80 more than the ones from the parts stores.

 

[miesk5]

Yo Jim,
Although relatively inexpensive, I would avoid Cardone reman PCMs.
jermil01 wrote, "In the past I've bought an EEC from these guys before. Good service and fast turn around. Plug in your info and you'll quickly find what you're looking for: Price is pretty reasonable.."
1995 Ford Bronco 5.8L V8 Gas ECM/PCM

 

[JimC25]

So I changed out the PCM and also tested the EGR and EVR, which both seemed good. Unfortunately, the new PCM didn't fix things. Still has surging idle on start until warm and power loss. My latest thought is the Knock Sensor, since it always gives me the code for it. I had kind of just been ignoring it before since no one sells them anymore. Has anyone ever found a source for these? If not, I read an old thread where Miesk suggested someone with a knock sensor issue advance their timing like for the Six-Liter tune up to account for the computer retarding the timing when it doesn't get a signal from the Knock Sensor. Thinking I'll give this a try and see if it helps. I'll set it around 13 to 13.5 and report the results.

 

[miesk5]

Yo Jim,
If you still has the old KS, plug it into the wiring harness & tape it up out of the way so it doesn't vibrate against anything solid.

 

[JimC25]

Thanks Miesk, May be a long shot, but I actually have a line on a new knock sensor through ebay. Once it comes in, I'll confirm if it matches the old one for anyone else looking. If it doesn't, then I'm going to adjust the timing as stated and I'll move the old one out of the way, but put it somewhere where it won't vibrate as you suggested.

 

[Timothyfugate]

My ‘89 is coming along, but it has erratic idle at startup, which evens out after 5-10 seconds if it doesn’t stall. Also, it has no power. It has the 5.0 with AOD transmission. The engine was recently rebuilt and I am about 400 miles into the break-in. So far I’ve replaced the O2 sensor, coolant temp sensor, idle air control valve, tps and map sensor. I also replaced the coffee can vacuum reservoir on the passenger side. I checked for vacuum leaks using carb cleaner and haven’t found any. Thinking it may be the ECM at this point, but interested in any thoughts on what I’m missing. Also only getting code for power steering pressure switch and knock sensor, 25 and 52. Thanks!

Check your computer brain mite not be right one for your engine swap

 

[JimC25]

Finally got back to the Bronco this weekend. I installed a new Knock Sensor I found on ebay with the same results. I checked codes after and I'm still getting Knock Sensor not detected (25), as well as 12 and 52 - RPM idle out of range and Power Steering Pressure Switch open.
I decided to adjust the timing to see if that helped in case the knock sensor issue was causing the computer to ****** the timing. The original timing was set at 10 degrees BTDC. When I tried to advance it, the distributor wouldn't turn any farther to do so. This made me think that the distributor might have been installed a tooth off, so I removed the distributor and re-installed it one tooth over. I then set the timing at 15 degrees BTDC and holy cow, what a difference!! My Bronco now has the power that I always thought it was supposed to have!!

I still have a bit of a hard start and the idle still drops intermittently after startup to the point that it often stalls, but if I give it a little gas when it drops and keep it going for about 20 seconds, it evens out and is fine. I'm going to keep playing with the timing and try to find the sweet spot, but at least the power loss part of my problem is solved for now!! I can't say if the timing solution is in any way related to the knock sensor issue, but it's running way better than it was before. More power and much more responsive!!

I'll keep investigating and posting updates.