Engine Update: Another rough idle thread

africansnowowl

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Apr 29, 2020
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To start, I've ran through the checklist about a hundred times. The car is an 87' GT 5spd, all original. The mileage is probably around 150,xxx. It idles at about 850rpm, but sounds and acts like it has an E cam. It accelerates fine and feels like it has the normal power it should, but it will buck at low rpms. Only engine mods are shorty headers, off road X, 70mm TB, dual electric fans, and a 3G alternator upgrade. It ran rough before those though. Do to a faulty DVOM I ended up replacing a lot of stuff that probably was fine, but here goes.
Started with the basics, plugs(gapped at 52), wires, cap, rotor, MSD coil. I also did "the fix" to the salt and pepper connectors.
Changed out the fuel pump, fuel filter, fuel pump relay, fuel pressure regulator. It holds 32 psi at idle, 42 with the vacuum line removed. Also replaced the injectors with known to be good explorer 19# injectors. Timing is set to 14 degrees.
It has 16" vacuum at idle. Changed out the PCV valve, screen, and grommet. I removed the smog pump, EGR valve, and capped all the vacuum lines going to the TAD, TAB, EVR, EGR... All the other vacuum lines were either good or replaced.
Replaced the O2 sensors, TPS, IAC, ACT, ECT, MAP, and put in the 70mm TB and EGR resistor. Also put a refurbished ECM in.
Verified all the grounds are good. Even added the new ground wire as recommended when doing the 3G upgrade.
Did the base idle reset procedure a few times. TPS set to .90, timing verified at 14. Only computer code it had was something canister purge valve related.
I pulled the plugs earlier today, all were dry with black soot. The car doesn't smoke or anything.
Is it possible the car just needs to be driven? It hasn't been driven but maybe 5 miles in the last 6 months. I know the gas in the tank is good. I used all Motorcraft sensors where applicable.
 
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Potomus Pete

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I would start by driving it. A classic car mechanic told my friend that had your problem to drive it. It was a smokey and the bandit Trans AM . He said to get it on the highway for a longer ride. Other than that you have done a lot. Driving like an E Cam usually is vacuum leak.
 

jrichker

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@africansnowowl

Dry with black soot spark plugs is a sign of a overly rich fuel mixture.
If someone connected the fuel tank vent line directly to the line coming off the intake manifold, that would give you an overly rich fuel mixture.

See the code 85 description below...

Code 85 CANP solenoid - The Carbon Canister solenoid is inoperative or missing.

Revised 11 –Jan_2015 to add warning about vacuum leaks due to deteriorated hose or missing caps on vacuum lines when the solenoid is removed.

Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

If you disconnected the carbon canister and failed to properly cap the vacuum line coming from under the upper intake manifold, you will have problems. You will also have problems if the remaining hose coming from under the upper intake manifold or caps for the vacuum line are sucking air.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.

Connecting the gas tank vent line directly to the intake manifold will result in fuel vapor being constantly sucked into the intake manifold. There is unmetered fuel that the computer cannot adjust for. The result is poor idle and poor fuel economy.



It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?


The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

The purge valve solenoid should be available at your local auto parts store.

Purge valve solenoid:



The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:
903_AIRTEX%20_pct_2F%20WELLS_7310014_1.jpg
 
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africansnowowl

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Thats a lot of good info. Just to be absolutely sure, I pulled the upper intake and replaced all the vacuum lines and put new hose clamps. It was a pain finding a line that matched the pre molded PCV hose, but I found something in the Help! section at Autozone that worked. While the manifold was off, I capped off the line that goes to the carbon canister. I also capped where the line goes to all the other emissions stuff like TAD, TAB, EVR, EGR... Made sure all lines that have anything to do with vacuum were brand new and secured with a hose clamp. So the only vacuum lines on the intake manifold are PCV, the one that goes to the MAP, fuel pressure reg line, and the source line that goes to the tree. The other ports are securely capped. On the tree, I just have the source, A/C line, and brake booster line. I tried isolating those systems while testing vacuum readings with no change. Still bounces between 14-16" of vacuum on the gauge.
Checked each plug wire, there is definitely spark leaving the cap. The fuel pressure is good. TPS is set and IAC seems to be working. Not sure what else. Cleared the codes again and let it warm up and the only code is 85, canister purge, which is expected.
 

africansnowowl

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When I went to recheck the timing today, I couldn't get the timing gun to work on the #1 plug wire, but it did work on other wires, so I ended up putting a new distributor and TFI in. That made absolutely no difference. The tank was almost completely empty, so I drove it a few miles down the road to fill it up. A full tank made no difference. In addition to the rough crappy idle, the rpms hang at 1500 if I shift out of gear into N. The car bucks and stumbles while lightly accelerating up through about 2000 rpm. After 2000 it seems to clear up. It also seems to clear up/not stumble if I accelerate somewhat hard. Engine being hot or cold doesn't matter, as it still idles rough/accelerates rough ether way. I'm going to pull the 10 pin connectors apart again tomorrow to make absolutely sure they are getting the best connection possible. Apart from that, I have no idea what else to look at.
 

Willybill32

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When I went to recheck the timing today, I couldn't get the timing gun to work on the #1 plug wire, but it did work on other wires, so I ended up putting a new distributor and TFI in. That made absolutely no difference. The tank was almost completely empty, so I drove it a few miles down the road to fill it up. A full tank made no difference. In addition to the rough crappy idle, the rpms hang at 1500 if I shift out of gear into N. The car bucks and stumbles while lightly accelerating up through about 2000 rpm. After 2000 it seems to clear up. It also seems to clear up/not stumble if I accelerate somewhat hard. Engine being hot or cold doesn't matter, as it still idles rough/accelerates rough ether way. I'm going to pull the 10 pin connectors apart again tomorrow to make absolutely sure they are getting the best connection possible. Apart from that, I have no idea what else to look at.
My understanding is that the vacuum canister is helpful if it’s hooked up. My ‘86 does have an E cam, and it bucks frequently at low engine speeds (<1200) and the tuner tells me it’s associated with the cam.
 

africansnowowl

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I intend to hook it back up, I was just trying to eliminate as many things that could be causing the issue as possible. I was going to clean and inspect the 10 pin connectors here in a little bit, but now I’m leaning towards deleting them. Has anyone cut them out and soldered wire in place of them? I saw a few YouTube videos of people doing this.
 

africansnowowl

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I went out and bought a fancy OBD1 scanner just to make sure. Key on engine off just an 85, or canister purge which is expected since it's not hooked up. Key on engine running I got a 13, 21, 33, 42, and 92.
This was at operating temp btw
 

africansnowowl

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I measured the O2 sensor voltage at the PCM today and noticed that the voltage doesn't cycle. It was holding a steady 0.9v. It did this for both sensors. Didn't seem to matter whether the engine was hot or cold, still got the same voltage readings. Is this something that could cause a crappy rich idle? The sensors are only a few months old. I also tested the fusable link which was good, and I am absolutely certain the HEGO ground is as good as it can be.
 

jrichker

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Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.


Alternator wiring.






If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.


Starter solenoid wiring 92-93 model cars.



The 42/92 code is because you have fuel being dumped into the engine not under computer control.
These are items suspect:
1.) Fuel pressure regulator:
[indent}
A. Not holding constant 37-41 PSI, the pressure is above this range The 39 PSI is where the injector flow rating is measured. The 2 PSI tolerance either above or below 39 PSI are taken care of by computer altering the injector pulse width.
B. Possible blocked or crimped fuel return line.
C. Adjustable regulator not correctly adjusted
D. Regulator has failed
E. Regulator diaphragm leaking fuel into the attached vacuum line coming from the intake manifold.
F. No vacuum on regulator diaphragm connection.
[/indent]
2.) Injectors stuck open.

Use a noid light to check each injector to make sure it is pulsing. You will need to remove the upper intake manifold and disable the fuel pump by removing the fuel pump relay. Crank the engine by using the ignition switch; move the noid light from one injector to the next. What sequence you use to check the flashing noid lights is not important. What is important is that the noid light(s) flash on and off. A noid light that does not flash, but stays on is where the problem is. The failure mode is either an injector stuck open because of a mechanical failure inside the injector or the control wire that goes to the computer has shorted to ground.
3.) Computer failure.

Computer failure is indicated when there are injectors that are stuck on because of shorts to ground when doing the noid test. Turn the ignition switch off and disconnect the computer connector from the computer. Rerun the noid test; none of the injectors should light up when tested.
4.). Code 85 Fuel Vapor canister plumbing incorrectly done.

A.) Connecting the gas tank vent line directly to the intake manifold
Connecting the gas tank vent line directly to the intake manifold will result in fuel vapor being constantly sucked into the intake manifold. There is unmetered fuel that the computer cannot adjust for. The result is poor idle and poor fuel economy.
B.) Charcoal canister plumbing.
One 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.
 
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africansnowowl

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My 3G alternator is wired as you described. I also added the recommended ground wire from the block to the ECM ground next to the battery.
The fuel pressure holds a steady 30-32psi at idle. 40 with the vacuum line removed. It is a new factory regulator, and there is no fuel in the line.
The computer is new(refurb). Also the injectors all check out both noid and having correct voltage. If I pull the plugs, they all look identical, which is dry with heavy black soot.
The canister vacuum line has been capped on the manifold for the time being. The purge valve was bad, so I just removed it until I get around to buying a new one. They’re not exactly cheap for some reason. But I am absolutely certain the vacuum system is all routed correctly and leak free.
Could a bad O2 harness cause the sensors to not cycle and hold the .9v?
 

jrichker

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My 3G alternator is wired as you described. I also added the recommended ground wire from the block to the ECM ground next to the battery.
The fuel pressure holds a steady 30-32psi at idle. 40 with the vacuum line removed. It is a new factory regulator, and there is no fuel in the line.
The computer is new(refurb). Also the injectors all check out both noid and having correct voltage. If I pull the plugs, they all look identical, which is dry with heavy black soot.
The canister vacuum line has been capped on the manifold for the time being. The purge valve was bad, so I just removed it until I get around to buying a new one. They’re not exactly cheap for some reason. But I am absolutely certain the vacuum system is all routed correctly and leak free.
Could a bad O2 harness cause the sensors to not cycle and hold the .9v?
The sensors are responding to what they sense. The .9 output voltage is because there is too rich a mixture present. Do the noid light check to make sure that there are no stuck injectors present.
 

africansnowowl

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Something I just noticed today, I have a cheap-o fuel pressure gauge connected to the Schrader valve. I notice it never leaves 0 when I prime the fuel pump. When I start the car it reads a normal 30psi at idle. Turn the car off and the pressure immediately drops to 0 again. Is this an internal fuel leak?, or is it just what a cheap fuel gauge does? There is no fuel leaking from the regulator(it's a new factory style from LMR) and the injectors are refurbished explorer injectors I got off eBay a few months ago from a shop that had a really good rating. The pump is a Delco assembly I got off Amazon a few months ago. The hoses definitely show their age, but I couldn't find any external fuel leaks.
 

africansnowowl

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I did the noid light test and all 8 injectors had the same intensity and pulse. I also checked the resistance of each injector which was around 15ohms. All 8 injectors also had 12v on the red wires.
 

Dan02gt

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Something I just noticed today, I have a cheap-o fuel pressure gauge connected to the Schrader valve. I notice it never leaves 0 when I prime the fuel pump. When I start the car it reads a normal 30psi at idle. Turn the car off and the pressure immediately drops to 0 again. Is this an internal fuel leak?, or is it just what a cheap fuel gauge does? There is no fuel leaking from the regulator(it's a new factory style from LMR) and the injectors are refurbished explorer injectors I got off eBay a few months ago from a shop that had a really good rating. The pump is a Delco assembly I got off Amazon a few months ago. The hoses definitely show their age, but I couldn't find any external fuel leaks.
There is a little S hose that goes from the fuel pump to the hanger. It is known to go bad and start leaking and can cause fuel pressure issues. Might be worth checking out.

I also have another thread on here where I talked about removing each pin from the 60 pin EEC connector and tighten them up like with the 10 pin connectors. That made a big difference in how my car runs.