ROUGH IDLE at times and down on power

FoMoCo17

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Apr 1, 2011
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I have gone through the surging idle checklist over and over. I'm pulling my hair out and wasting so much time!

1990 Mustang GT. Stock engine except roller rockers, kenne bell supercharger, cold air intake, new accel injectors and timing chain, MSD billet distributor, MSD coil, Flex-a-Lite cooling module.

Here's what I know:

Intermittent Code 96: Cant locate or find the problem! Code definitions vary from secondary power circuit as the problem. Or, power to the ECU. And, possibly the primary circuit but this should set a code 95 from what I know. Checked all circuits and am not finding anything.

Engine sporaticaly misses and runs rough when timing light is transferred to different plug wires. Took MSD super conductor wires off ... seems to run just a hair better. Still have MSD coil on it but may change back to stock on that too. All brand new stuff.

Engine is down on the vacuum gauge averaging about 14 in hg. As I go up some inclines it drops to just about zero but cruises at 18-20 no load. And on decel it goes up to 22-23 from what i recall.

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Timing set @ 8 degrees BTDC as per Kenne Bell with 93 octane gas.

HEGO - 3.6 Ohms between heater (spec calls for 2-5 Ohms). Have battery voltage with key "on" harness side (disconnected) between power wire and I believe signal return wire as book says I should have. Sensors were replaced 2 years ago and have about 5,000 miles on them

Bat ground to test connector "signal return" wire - 1.6 ohms
Bat ground to TPS - 1.6 ohms
Bat ground to ECT 1.7 ohms
Bat ground to EGR - 1.6 ohms
Bat ground to ACT - can't get to it ... under supercharger ... just replaced ACT ... checked circuit when supercharger was off and it was okay. no codes relating to this.

ECT Ohms out and matches temp/resistance chart in my book at whatever temp the motor is.


Ign/Key On

IAC - battery voltage on one wire - return wire showed .55 volts.

TPS - VREF wire shows 4.97 volts. TPS voltage setting .96 volts

EGR - VREF wire shows 4.97 volts couldn't get to other wires ... no egr codes

ECT - VREF wire shows 4.68 volts ... return wire shows .08 volts measuring with the connector off. With connector on VREF was around 2.1 volts due to the resistance. This voltage reading checked out with chart in my book.

MAP/BP

Connector disconnected: Measured 5.0 volts on MAP/BP signal wire and 5.0 volts on VREF. IS THIS CORRECT WITH THE CONNECTOR DISCONNECTED?


Checked pins 20, 40, 60, 46, and a few other pins on 60 pin connector to BAT ground ... not more than 2 ohms. All injectors showing BAT voltage on 60 pin connector.

Checked for vacuum leaks, cant find any. Disconnected all lines .. no vacuum change. Checked with propane nothing ... though with supercharger on motor, its almost impossible to check manifolds etc. except near front of motor. Cleaned EGR valve, MAF sensor, and IAC valve numerous times. Reset idle several times. Just barely idles with IAC disconnected sometimes cuts out.

Fuel pressure checked: 32 psi w/vacuum and 39 w/out vacuum or possibly 42 (its been awhile. Pressure was steady and system holds pressure as it should. New fuel pump and regulator installed two years ago including new gas tank.

Compression test done measure fairly uniform around 120-125 psi one was 115 psi using a Harbor Freight gauge. Leakdown test showed a low leakage rate (not sure what it was but it was good). Pressure tested cooling system ... no leakdown after 20 minutes.

Car runs great other than what is listed above at the top. Just do not understand what is causing these problems. Idle is better after putting 20 year old plug wires back on rather than new MSD wires but still gets bad at idle at redlights or taking off sometimes it spits and sputters. I find it is better to start it and immediately throw it into gear and start driving rather than let it idle and be all choppy. However, at red lights sometimes I find myself throwing it in park to even it out some though it feels like it is still running rough. Normal driving, there is hesitation especially can be felt in overdrive cruising at 45-50 light load.

What else can I do ... feel like I am chasing a chicken with its head cut off but not catching it! I'm great with cars and have a lot of technical expertise on these cars but get some weird problems on my own cars. I do much better at solving other Mustang owners problems ... that is why I have taken the time to give you all of the information I have to date. Any good ideas will certainly be entertained and I look forward to help in resolving this/these conditions.

Oh, I do have a header leak at the collector ... got new headers ... just gotta find the time to install them while going through checking things as I think of them each day. Just got rear-ended by a guy behind me at a redlight who decides to take off into my bumper after he stopped for the red ... idiots. Anyway, I will be fixing the headers and rear bumper but also want to get new ideas and or opinions because I'm out of ideas!!! thank you , in advance for your help!
 
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jrichker

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1.) What kind of air intake system do you have and where does it pull air from?
2.) What kind of MAF do you have? Is it matched to the injector size?
3.) Clocking the MAF is useful when you have a cold air kit or some other modification to the air box or air inlet before the MAF. Clocking is turning the MAF housing so that the sensor element is in a different position. It changes the airflow through the MAF to place the sensor pickup in the place where the airflow is the least disturbed.
4.) Have you checked the O2 sensor ground? The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

As always, See the "Surging Idle Checklist for help with all your idle/stall problems.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.
 

FoMoCo17

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Apr 1, 2011
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I have the original Ford MAF sensor with new 19 lb/hr. Accel injectors so they are matched. I have the stock lower intake with a Kenne Bell upper manifold then back to the supercharger ... then a Kenne Bell inlet manifold that the EGR plate and throttle body bolt to. I also have a BBK cold air intake system which is routed into the fenderwell area. I have not "clocked the MAF yet but will give it a try to the outer side of flow and see if that makes a difference. However, the misfiring evidenced with the timing light on random cylinders has really puzzled me cuz it seems to mimick the way the engine misses at times!

Yes, checked the HEGO ground on the back of the manifold this past Winter when the supercharger was off. Possibly I should check the ground on the oxygen sensors back to the battery also ... but i'm sure it is good ... but will check it when I have a chance.

Yes, I have tried just about everything on the surging idle checklist that I can get to w/o disassembling the engine. When I had things off the top of the motor over the Winter, I went through it and checked grounds, connections, etc. that was part of the purpose in taking some things apart ... to check everything possible ... but found nothing other than a few small ground problems that were higher than they should be.

Any other suggestions would be most helpful!
 

jrichker

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1.) Do a cylinder balance test to make sure that there are no cylinders that consistently report back as weak.
Cylinder balance test:
The computer has a cylinder balance test that helps locate cylinder with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.


Here's how to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

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If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Cylinder balance test
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure


Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.

2.) If you find random cylinders that fail when you do the cylinder balance test (different cylinders each time you do the test), be sure that the IAC will hold the 1400-1600 RPM needed for the test. If it does and you still have random failing cylinders, the PIP sensor in the distributor is failing, or you have a spark leak in the distributor rotor or cap.
 

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FoMoCo17

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Apr 1, 2011
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Cylinder balance test was one of the first things I did and it has always come back good with a "9" so no further need to retest.

Clocked MAF tonight no change ... will clock it in opposite direction.

I think I have three problems:

1.) The code 96 (continuious memory) which is described in 3 different manners as listed in my original post regarding the true code definition.

2.) Some sort of ignition problem cuz it misses at idle and off idle but everything has been checked and/or replaced and checked again. Just seems to "miss" randomly a lot causing a crappy idle.

3.) Some sort of vacuum/leak problem. Noticed tonight when I got into it half the way, vacuum was at 10 in Hg. but immediately dropped to "0" Hg. became "raspy" while climbing a hill ... let off a bit at top of hill and vacuum gauge just jumped quickly back to 10-12 in Hg. Seen this several times. Sometimes its at 10 in Hg. and just drops to 0 in Hg. when it is not being loaded any further. I thought it had to be in the EGR system, Air Pump system or Charcoal Canister system but haven't found anything after checking these systems out. They are the only three systems that "kick in" when the engine is running during moderate to heavy cruise that I am aware of.

So, this is what I am seeing and experiencing. Since i have checked everything so many times, checking new ideas or a different way of checking things would be helpful.

I look forward to solving this matter so help is needed to stop the wild goose chase. Thank you.
 

jrichker

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What sort of vacuum are you pulling at idle with the transmission in neutral? You should see 16"-19" at idle, and 18"-21" at 1000 RPM.
 

FoMoCo17

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Apr 1, 2011
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Depends how it is running, usually 14-16 in hg. in neutral. If its in one of its idle fits 13-14 in hg. ... if not usually I get 15 in hg. when its running good at idle. Around 1,000 rpm, its usually 16-17 in hg. In drive, it drops to 12 in hg. when its running crappy and 14 in hg. if it running good in drive

Found a small vacuum leak today though it didn't change my readings whatsoever even though it seemed like a decent leak. Just do not know what else to check ... strangers notice it and think I have a cam in it ... so it is noticeable when it gets in one of its fits. During initial start up, the IAC holds the rpm's up for the first 20 seconds and it feels good but when it goes to idle, it usually starts running rough .... that's when I usually just throw it into drive and go .... then it hesitates a little bit while accelerating .... then once its warmed up, it drives pretty good until it idles too long at a light or I come to my destination and let it idle ... then it starts running rough. These sort of problems sure take the fun out of this car cuz sometimes solving such problems is never ending.
 

jrichker

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The low vaccum at idle indicates you have vacuum leak(s) somewhere. Your problem will not clear up until you have fixed them.


There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and every hose and connection.

Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine that it may be difficult to detect small leaks. The engine in my first Mustang pulled about 16.5" of vacuum at 650-7250 RPM, which I consider rather low. It was a mass market remanufactured rebuild, so no telling what kind of camshaft it had. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed. Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Fire is an excellent hair removal agent, and no eyebrows is not cool...

The vacuum line plumbing is old and brittle on many of these cars, so replacing the lines with new hose is a good plan. The common 1/8” and ¼” vacuum hose works well and isn’t expensive.

The PCV grommet and the power brake booster check valve grommet are two places that often get overlooked when checking for vacuum leaks. The rubber grommets get hard and lose their ability to seal properly.

Fuel injector O rings can get old and hard. When they do, they are prone to leaking once the engine warms up. This can be difficult to troubleshoot, since it is almost impossible to get to the injectors to squirt oil into the fuel injector mounting bosses. If the plastic caps on the fuel injectors (pintle caps) are missing, the O rings will slide off the injectors and fall into the intake manifold.

Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $3-$4 per kit. The following are listed at the Borg-Warner site ( http://www.borg-warner.com ) as being resellers of Borg-Warner parts:
http://www.partsplus.com/ or http://www.autovalue.com/ or http://www.pepboys.com/ or http://www.federatedautoparts.com/

Most of the links above have store locators for find a store in your area.

Use motor oil on the O rings when you re-assemble them & everything will slide into place. The gasoline will wash away any excess oil that gets in the wrong places and it will burn up in the combustion chamber. Heat the pintle caps in boiling water to soften them to make them easier to install.



Diagram courtesy of Tmoss & Stang&2birds
mustangFoxFordVacuumDiagram.jpg



Vacuum leak due to slipped lower intake manifold gasket...

Ask Nicoleb3x3 about the intake gasket that slipped out of place and caused idle and vacuum leak problems that could not be seen or found by external examination. I don't care what you spray with, you won't find the leak when it is sucking air from the lifter valley. It simply isn't possible to spray anything in there with the lower manifold bolted in place.

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See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif
 

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FoMoCo17

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Apr 1, 2011
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I'll keep searching for the vacuum leaks!

I did notice something beculiar this evening. I unplugged the SPOUT connector (like your setting timing) and noticed that the engine ran a little bit worse and missed all of the way up to about 1,700 rpm. You could just hear it sputtering. I think part of my problem is in the ignition system (might even raise the vacuum if it weren't missing as much) also. I have a brand new distributor from MSD and did it with old MSD distributor (last year) so distributor should be good. Pulled MSD coil off and MSD wires and installed original OEM wires/coil helped slightly but nothing significant. Plugs are Autolite Platinums (center electrode) 24's gapped at .035" for the supercharger. Ignition misses show up with timing light installed on different wires ... just do not understand what is causing this intermittent misfiring. Also had Autolite 24 copper core plugs and they acted the same. Any ideas would be helpful.