Engine mis-fire/ shutter / skip

[svxcuseme]

The grease is only used on the inside of the boot to help it seal and prevent the boot from sticking on the plug. I used Dielectric Tune up grease from Permatek.

This could fix a spark leak issue but I don't think the major stumbling issue is caused by this type leak. My coil was on it's way out and I went from minor stumbling under load to total coil failure and extremely poor driveability when warm.

I replaced the boots and sealed them and still had my faulty coils so my results are inconclusive as to whether the spark leak was really the root cause of the stumbling. I'm sure it was a contributing factor.

[Beav]

It all depends on how much damage has already occurred.

The grease goes inside the boot - it doesn't take much.

Why in hades would you use silicone grease with graphite?? Isn't graphite a conductor? Hmmm?? The entire purpose of using it is to form a dielectric seal, the greasy part not allowing the rubber to stick is just a nice bonus.

[svxcuseme]

Typo...............

[svx_commuter]

My SVX is having this same problem and GETTING WORSE. It has a rough idle now when it's cold. I a AT code and it say TPS, so I checked the sensor and it's good. However, the resistance readings to ground on get on the connector for the TPS are not what the book says they should be. They are all supposed to be 1mega ohm and I get:
1 is only .7ohms that is point 7 ohms.
2 is 600,000 ohms
and 3 is 810,000 ohms

So before I start ripping apart the inside to get that ECU has anyone or can any one please check the values for this?

Maybe this is just my error since the connector at the ECU is not disconnected.

Thanks and take care too,
John

[svx_commuter]

I replaced a bad coil yesterday and it is running better but different. The sumbling is gone and I made it up the hills with TC locked up, so that all looks good. The bad coils was just plan dead, no spark at all out of that. I have to drive the SVX for awhile to see how it's changed.

There is something strange going on. I cleaned out the TB two weeks ago when the miss started and then the idle was high. I found the hose for the fuel pressure rgulator was off and reconnected. This dropped the idle speed some. Then I adjusted the TPS to 5 volts. This is the strange part.

The position for the TPS was was all the way off to one side and not in the middle of the slot any more. It has always been close to the middle of the slot. I checked it agian yesterday and with another TPS, sfter replacing the coil and I get the samething, way off to the side.

What changes the position of the TPS setting beside the resistance of the TPS, applied voltage and TB shaft position? I know the shaft hasn't moved and the resistance is the same so I am thinking the applied voltage must have changed some how. Maybe this is psrt of the ECU learning curcuit? I tried to reset the ECU a few times by pulling fuse 14 for a few minutes but that has no effect on the idle.

It is also stranage that the power light did NOT come this morning.

Thanks and take care too,
John

[Beav]

Battery voltage varies between 8 and 15 volts depending on electrical system load. To ensure accurate signals, a voltage regulator is included in the module to eliminate voltage fluctuations from the battery.

This steady source voltage (typically 5 volts) is referred to as Reference Voltage or VREF. Input devices (sensors) require a steady source voltage in order to provide accurate information about system operation.

In addition to a steady source voltage, input devices need a reliable ground. This ground is known as signal return and is dedicated to input devices and always returns to the module. Only input devices should be attached to this circuit; adding other devices could cause inaccurate readings by the module.

A potentiometer is a type of variable resistor (voltage divider) that produces an analog DC signal. It is commonly used to convert mechanical position into an electrical signal.

Potentiometers are used in electronic systems where the module needs to determine the position of a component. Potentiometers are typically composed of a resistive material and a moveable wiper with the following electrical connections:

reference voltage (VREF)
signal voltage
signal return (ground).


Voltage is applied to one end of the resistive material. The other end of the resistive material is connected to a signal return (ground). The movable wiper arm in the potentiometer is attached to the signal voltage circuit. The tip of the wiper contacts the resistive material.

The wiper arm follows the movement of the component it is monitoring. As the wiper moves, the voltage signal to the module increases or decreases.


John, you need to check your VREF (5vdc) and ground connections. Do a voltage drop test on them if necessary. Use a small light bulb for a load. Measuring resistance is really a poor test of a circuit - there is no load to 'aggravate' devices and connections. I recall your test board - if you apply power and ground then attach a very low current load on the signal wire (think #194 bulb or smaller), along with a voltmeter, you'll get a much more accurate display.

Anyway, I'd check my grounds closely. They could also be the cause of your other concerns.

[svx_commuter]

Okay Beav I with you on the VREF.
I looked at the engine ground connection and it looks good and clean. I also checked the resistance from the neg bat terminal to the engine and it was really low at .1 ohms. I don't know if this reading changes under load. Now I have to check the TCU ground. Right?
I am getting a blinking power light that says the TCU thinks the TPS has an open circuit, so something is really off in voltage land. The AT is shifting very different than normal and the mpg has dropped from 27 to 23.
I think I am going to have to back probe the TCU and check the voltages as you say.

The TCU is such a pain to get to and back probe. I always end up with my neck twisted and stiff the next day.

Where is the ground wire for the TCU and ECU?

The engine is running very smooth since I replaced the coil, no more missing and stumbling. I hope the current problem with TPS or TCU is not some how related to the coil failure.

Finding the bad coil was easy since it was totally gone. I unplugged one fuel injector at a time to see if the engine miss stayed or got worse. If it got worse I plugged it back in and tried the next one. When I unplugged the injector that went to the bad coil there was no change in the miss. It was the middle cylinder on the drive side and I surprise myself by getting it out and replaced even though it was a tough place to get the hands into but a lot quicker then pulling out the battery. Thanks to the people that make vinyl gloves. Save my hands to work another day.

Checked the replacement coil with a used spark plug installed and the coil laying on top of the engine intake, injector disconnected, run the engine and it has a good spark. Check the old coil the same way and NO spark at all. Check the replacement one going in again and it’s still okay. Then checked the bad one again and it’s still bad. It all seemed too easy of a way to check the coil. This replacement coil has about 90k miles on it, the one that when bad had 276k miles. I guess it was due?

[svx_commuter]

I searched and found this,
Quote>>
The rule of thumb appears to be always suspect a ground fault, but I do not go along with such a simple approach. Surely if the TCU was not properly grounded several associated faults would show up.

N. B. ---- You are correct with the ground connections. The TCU is grounded via a black lead which goes all the way back to a common point within the transmission housing. This is done to prevent an earth loop which could otherwise result in interference signals on the high impedence input circuits. Do NOT attach a direct ground wire from the TCU to any other place.

I am swearing for you, Trevor.<<end Quote

Thanks Trevor (lurking?) and take care too,
John

[svxcuseme]

As far as the mileage... I average 23 with a mix of highway and city streets. I've always gotten around 23... If you had 27 , I'm jealous.

[Beav]

Yah, it's o.k. to repair circuits but only from their original connection points - don't change their locations and expect things to work properly.

John, you really need to forget that you have an ohmmeter. They'll give you more troubles than cures when checking circuits. Measuring voltage drop is the way to go. I like to disconnect both ends of a circuit and pass power through to an old headlamp that has one terminal grounded. When it is powered-up begin wiggling wires, connections, etc. With an ohmmeter the crappiest connection probably won't register a fault but that big, old headlamp will flicker. You can even place the positive lead from your voltmeter on the powered side of the headlamp and watch the voltage drop.

[svx_commuter]

Well that was an interesting day, yesterday, all my troubles seemed so far away and then my AT started to shift hard and the RWD began to bind at low speeds. So when I got home I figured I’d get the TCU codes. I ran thru the gear shift movements and step on the accel pedal and I GET NOTHING. Oh man no blinking power light at all. I try it again since I think I must have messed up and still no codes. Turn the SVX on and there it is blinking power light telling me something is wrong. I go and get the other TPS that I have and put it in. I try to get the codes again and it still will not kick in when I step on the accel pedal. Then I do other “things” to look for the problem.

Short story is everything looks okay this morning after the things I did. I drove all the way to work and accessed the TCU when I got here and it gives the OK everything is okay blinking.

I really think the fix was disconnecting the negative battery terminal overnight and I’ll let you know in a few days if it stays fixed. The reason I say this is because all the other things did not change any of the voltage readings or allow me to access the memory of the TCU.

Here are the other “things” I did if you want to get totally bored then read on. Dropped the ECU TCU down to access wires and what a pain in the neck I find this to be. I am not a big person and I don’t know how a large person can get under the dashboard to do this. The three nuts that have to come off are buried inside the dashboard, ECU and TCU come out together, can’t get one without the other, roll apart easily from each other but what a pain to put them back. Then I get the FSM and find the pages for the wire numbers and connector numbering, get the voltmeter and back probe the connectors.

This is always interesting as I never remember if the picture in the FMS is looking at the connector side or the TCU with the connector removed. So sometimes I got the wrong wire. It doesn’t make it any easier lying upside down or looking at the connectors backwards because the short wires keep everything under the dash and prevent the ECU and TCU under the dash.

The ECU supply voltage was fine at 14 volts. Then I checked the voltage to the TPS at the TCU connector, engine switch on, and it was reading millivolts and not the 4 volt range it was supposed to have. It was also supposed to change when the accell pedal is pushed and it did not change. So that looked like a BIG problem.

Then I found the three wires in the ECU connector that connect the TPS. One of the three wires supplies the voltage I was back probing on the TCU. So I was able to check the resistance of back probing setup (to see how well I do at back probing) by connecting to the wire on the ECU that connects to TCU. It was okay at about .3 ohms.

So then I pulled all the connectors off the TCU and ECU and TPS and checked the resistance in each wire connector to connector. One of the wires was reading 2.2 ohms and not .3 ohms as the other two were. Yeah I use an old inexpensive digital multimeter. So then I opened up the wire connectors to the engine and AT. The four engine connectors are under the plastic intake so that had to come off. The two AT connectors are under the firewall above the AT housing. I cleaned them with tuner cleaner and snapped them back together. I also cleaned the ground connector between the engine and firewall. Then I checked the readings at the TCU and I was still not getting the right voltage and it still did not change when I stepped on the accell pedal. So I started the engine and it ran. I turned the TPS all the way to one side for the slowest idle since my idle has always been on the high side. Then I tried to get the TCU stored codes again and got nothing. This is when I disconnected the battery and left it that way until this morning. This is also known to me as the “Larry Fix”. He always recommended this for most problems with the engine or AT. I am thinking I will start to do this about once a month. Perhaps the ECU and TCU got all mixed up when the coil went? At any rate the battery has been disconnected over night for since at least a year ago.

Thanks Beav for the insight on the current drain. I have to put the test set-up together for that. I have to try something again. I think I tried to change the idle speed a few years ago by adjusting the TPS, about a day after the adjustment the idle speed was back to where it was before moving the TPS. I want to know why?

Take care Too,
John

[Beav]

Originally Posted by svx_commuter

I think I tried to change the idle speed a few years ago by adjusting the TPS, about a day after the adjustment the idle speed was back to where it was before moving the TPS. I want to know why?
John

That is what computer 'learning' is all about. Imagine several sensors, labeled A - F. When A B C D & E = x, F should = y. If F doesn't = y the computer 'learns'/compensates by making the new 'y' value the 'new normal' spec for those conditions.

The reason for all of this is because as sensors and circuits age they build resistance. As this resistance grows the values expected change. The engineers designed these tables to compensate for this anomaly and stay within the EPA guidelines for how many years/miles they had to guarantee the car's emission reliability.

[Motorsport-SVX]

alcyonegirlys blue 94 has had this "miss" for the last
few weeks, I think its either a faulty injector or coil
we are on the verge of tracking it down on her next day
off.

my car has the "flat spot" during excelleration then
suddenly taking off situation, and Now just the last
few days the "engine dieing" out of the blue and restarts
sometimes, and sometimes not, running bad etc.
Options of things to look at there are:
bad alternator, broken ground etc....maybe they are tied
in with your problem too.
Im also going to check my fuel pressure and fuel pump.

My mpg is down to 12-14 in town...
last 30 days of 105-110 temps not helping things either.
hope to figue our problems out this week.

[Beav]

A sudden, drastic mpg drop and stalling? I'd swap the MAF before doing a lot of investigating.

[Motorsport-SVX]

Originally Posted by Beav

A sudden, drastic mpg drop and stalling? I'd swap the MAF before doing a lot of investigating.

Did that already, w/ two seperate (used) units