Hot Start Problems

[KonaCrash]

Hi everyone,

I have a 1995 Discovery 3.9L V8 MFI, left hand drive, with 97,000 miles that I've had for about 3 years. There are no modifications and I keep it on the roads.

About 6 months ago I started getting the check engine indicator and fault code 48 for the stepper motor / idle control valve. I reset the fault and it would come back every week or two. Since then it has progressed to rougher starts and twice has not started at all, the fault code comes every day or two now. When the engine is cool, or is restarted almost immediately (less than time to fill the gas tank) it starts up perfectly. When the rough starts occur it is always after the engine is at operating temps and the car has been parked for between 5 and 30 minutes. During these rough starts the engine fires and the RPMs go to 1500 and then as it settles down to idle it begins to faulter and sound like the pistons are going to go through the hood when the RPMs start to drop below 500 and would die if I didn't give it the acellerator to keep the RPMs up around 1000. After a minute or two of keeping the RPMs at 1000 I'll let it go back to normal idle, then I can drive away and it runs perfectly like nothing ever happened. On the two occassions that it didn't start at all, the engine would crank and turn over but would not fire - waited a half hour and then it started right up and ran fine.

Here is what I have done to the car while trying to fix this problem, in order
None of these seemed to improve or worsen the condition.
replaced pcv restrictor and hoses
replaced all the vacuum hoses
replaced O ring on stepper motor
replaced spark plugs (Bosch), plug wires (BWD), distributor cap and rotor button (BWD I think)
replaced stepper motor
air intakes look pretty clean
replaced fuel filter (Fram)
replaced coolant temperature sensor and washer
replaced fuel temperature sensor (Lucas)


A couple seemingly unrelated repairs during this time:
replaced bleed hose from coolant tank to radiator
replaced fuel tank filler breather hose
repaired rear window ECU by replacing solder joint on ECU
replaced A/C hose and refill.

I'm starting to go a bit crazy trying to fix this but I can't afford to keep throwing money at it.
These are some things I'm considering and could really use some help in what I should do.
1. I just noticed the under side of the throttle position sensor has two copper wires exposed - could this cause the problem. Can I use electrical tape to cover or is the heat too much?
2. After filling gas tank, I usually get a rough start as described above, could the release of pressure in gas tank contribute to that? fuel pressure regulator?
3. grounding problem? I cleaned off one near the battery, but where are other locations
4. spark. Is there a problem with distributor or ignition coil. I was going to use a spare spark plug to check for spark. I also just got a test light to check on coil too. Probably this weekend.
5. The main relay and fuel pump relay? I thought I read somewhere heat can be a problem for them sometimes.
6. When I replaced the fuel temp sensor last night, I pulled off the pcv hoses for access and there was a little oil inside the hoses...is that normal?
7. am I right in thinking this disco is not OBD II compliant? it only has the fault code output under the passanger seat, right?

Sorry for being so long, I wanted to give as complete of a picture as I could. This is my first post, but this forum has been a great resource for me and my wallet. Thank you all very much.

Eric

[joey]

Eric, try disconnecting the MAF for a couple a starts and see if this helps.

[beemer]

Originally Posted by KonaCrash

Hi everyone,

I have a 1995 Discovery 3.9L V8 MFI, left hand drive, with 97,000 miles that I've had for about 3 years. There are no modifications and I keep it on the roads.

About 6 months ago I started getting the check engine indicator and fault code 48 for the stepper motor / idle control valve. I reset the fault and it would come back every week or two. Since then it has progressed to rougher starts and twice has not started at all, the fault code comes every day or two now. When the engine is cool, or is restarted almost immediately (less than time to fill the gas tank) it starts up perfectly. When the rough starts occur it is always after the engine is at operating temps and the car has been parked for between 5 and 30 minutes. During these rough starts the engine fires and the RPMs go to 1500 and then as it settles down to idle it begins to faulter and sound like the pistons are going to go through the hood when the RPMs start to drop below 500 and would die if I didn't give it the acellerator to keep the RPMs up around 1000. After a minute or two of keeping the RPMs at 1000 I'll let it go back to normal idle, then I can drive away and it runs perfectly like nothing ever happened. On the two occassions that it didn't start at all, the engine would crank and turn over but would not fire - waited a half hour and then it started right up and ran fine.

Here is what I have done to the car while trying to fix this problem, in order
None of these seemed to improve or worsen the condition.
replaced pcv restrictor and hoses
replaced all the vacuum hoses
replaced O ring on stepper motor
replaced spark plugs (Bosch), plug wires (BWD), distributor cap and rotor button (BWD I think)
replaced stepper motor
air intakes look pretty clean
replaced fuel filter (Fram)
replaced coolant temperature sensor and washer
replaced fuel temperature sensor (Lucas)


A couple seemingly unrelated repairs during this time:
replaced bleed hose from coolant tank to radiator
replaced fuel tank filler breather hose
repaired rear window ECU by replacing solder joint on ECU
replaced A/C hose and refill.

I'm starting to go a bit crazy trying to fix this but I can't afford to keep throwing money at it.
These are some things I'm considering and could really use some help in what I should do.
1. I just noticed the under side of the throttle position sensor has two copper wires exposed - could this cause the problem. Can I use electrical tape to cover or is the heat too much?
2. After filling gas tank, I usually get a rough start as described above, could the release of pressure in gas tank contribute to that? fuel pressure regulator?
3. grounding problem? I cleaned off one near the battery, but where are other locations
4. spark. Is there a problem with distributor or ignition coil. I was going to use a spare spark plug to check for spark. I also just got a test light to check on coil too. Probably this weekend.
5. The main relay and fuel pump relay? I thought I read somewhere heat can be a problem for them sometimes.
6. When I replaced the fuel temp sensor last night, I pulled off the pcv hoses for access and there was a little oil inside the hoses...is that normal?
7. am I right in thinking this disco is not OBD II compliant? it only has the fault code output under the passanger seat, right?

Sorry for being so long, I wanted to give as complete of a picture as I could. This is my first post, but this forum has been a great resource for me and my wallet. Thank you all very much.

Eric

That stepper motor is the same damn thing as on the Camaro V6, i've collected many from Pick N Pulls. Even your parts stores have them for around $47.
Did you give it a short blast with carb cleaner, have it wired in but not installed then turn on the ignition and bump the starter, you'll see the plunger go in and out when you turn off the key again. This to get the carb cleaner to work in then air blast dry. I then use lock-ease a liquid with graphite for kocks as it will dry and let the graphite lube the stepper motor plunger drive internally. I've saved replacing them may of times by doing this the past 15 years.

[greg409]

Does the 3.9 w/dist use a crank pos sensor?

Both of mine resolved hot start by replacing sensor ($70@ dealer)

luck,greg

Let me amend:

rave cd (free) go to:
workshop manual
electrical
fault diag.
lucas ign.

Good stuff


luck,greg

[KonaCrash]

Thanks for the help guys.

I think I might have spoken too soon on the fuel temperature sensor. It seems to be running better and I'm only getting the fault light every couple days now. I think the computer might have to readjust a bit after running for 6 months with the bad fuel temp sensor. I don't know...give it a week or two and check it out.

Greg, I don't think the '95 has the crank sensor. I don't think that came along until the distributorless system came in, but I'm not positive.

Beemer, I've got a new stepper motor in there, so it should be clean.

Joey, should I start it up and shut it down a few times quick with the MAF sensor off, or start it up and run it awhile off, or go drive around a bit with it off?

thanks again.

[KonaCrash]

Got stranded for an hour again. I tried pulling off the MAF sensor, but that didn't help the hot start. Also checked the plugs for spark and it had good spark. Two mechanics happened to be next to my car when this happened and they took a look. They thought fuel pressure might be problem and thought I should focus on the fuel pump relay and the fuel pressure regulator.

The fault #48 doesn't seem to be coming as frequently and it seems to be running better at idle. But then it wouldn't start after stopping at the grocery store.

Maybe it is two different problems going on. I'm thinking I should replace the fuel pump relay. One supplier (British Parts of Utah) says that it needs 2, is that right? Also, should I replace the main relay as well or is that the second relay BPoU is talking about?

Any thoughts or comments are very much appreciated.

Aloha,
Eric

[joey]

Hot start issues could be fuel related, check fuel pressure... or Crank Position Sensor... change it, it isn't that expensive.

[KonaCrash]

Thanks Joey. I am going to see if I can rent a pressure gauge from checker this weekend.

Does the 95 discovery have a crankshaft position sensor? That was something that kept coming up in other threads when I first started looking into my problem, but I couldn't find any suppliers that had one for a 95. I think it wasn't until the GEMS engine with no distributor came into the 96 that the crank position sensor started being used. But I'm not sure about that, so if someone could confirm that would be helpful.

I'm going to unhook the battery for 10 minutes see if resetting the computer will help too.

[greg409]

The '95 does not have a crank pos sensor, I mentioned above, for ignition issues there's excellent diagnostics in the rave manual

If your truck runs ok most of the time & has spark when it won't start, then it's a fuel issue.

If you have a schraeder (tire type) port on driver's side fuel rail, you can borrow a buddy's
tire gauge & check fuel pressure as someone turns on the key

I used my wife's gauge.
(35# @ idle)

luck,greg

[beemer]

Originally Posted by greg409

The '95 does not have a crank pos sensor, I mentioned above, for ignition issues there's excellent diagnostics in the rave manual

If your truck runs ok most of the time & has spark when it won't start, then it's a fuel issue.

If you have a schraeder (tire type) port on driver's side fuel rail, you can borrow a buddy's
tire gauge & check fuel pressure as someone turns on the key

I used my wife's gauge.
(35# @ idle)

luck,greg

That would be on the right side of the fuel rail for the schraeder valve fitting not the left unless you can reach under the ram tube base and plenum on the left going after the fuel temp sensor. 95 D1 owner here, 4.6 no part is stock.