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Jim
| | Posted on Monday, October 21, 2002 - 12:02 pm: | 
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Hey guys, need your help in diagnosing my '94 DiscoI. Here's the story: (I've included quite a few details, maybe there's a clue)it's a 3.9 petrol, bone stock and I (reluctantly) admit that I haven't been very up to date on routine maintenance.
I'd been doing the surge-and-lurch above 50mph and figured it was the VSS. While waiting for the part to arrive from AB I decided to pull the old one, blow it out and put a little dry film lubricant on it. It was sticky and slow-turning when I pulled it and the dry-lube allowed it to spin quite freely. After I put it back in, it seemed to help although I still felt the occasional stumble at speed.
Yesterday, (85 degrees, sunny and dry) I shut the car off, ran a quick errand and when I fired it back up, *poof* runs like dog-shit. Idles rough and when I touch the accelerator the motor quits like I blew out a match. If I do a little dance on the gas pedal I can get it to idle up, but it sounds like a 5-pack-per-day smoker clearing his throat. I can drive it but it takes two feet and a constant recital of Hail Mary's.
This morning, started it up (seems to start up well enough, idle is a little rough) but as it warms up it seems to worsen. Cap and rotor look fine, no dash warning lights are lit (except for the ever-present ABS light). I can't imagine that the VSS could be the sole problem, what do y'all think? MAF? ECU?
What can I check? Where should I start?
Any/all help is appreciated. Free beer at my house!
-Jim |
Paul T. Schram (Paulschram)
| | Posted on Monday, October 21, 2002 - 12:27 pm: |
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Jim:
Start with the basics, compression, fuel, spark...
You admitted that maintenance has not been regular. When did you last change plugs/wires/cap/rotor (regardless of visual appearance)? Fuel filter?
You have a '94, you're not still running original plug wires are you?
How many miles? Since last tune-up?
These vehicles are forgiving, but not about their regular maintenance, just ask my rover-orphaned wife. Yes, you really do need to open the bonnet every time you drive into the driveway, and every time you get fuel!
Peace,
Paul |
Jim
| | Posted on Monday, October 21, 2002 - 12:58 pm: |
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Thanks Paul, I'm getting spark off the coil wire, and if I depress the tire valve-looking fitting on the fuel rail it'll spit fuel at me. I haven't done a compression test but it has the same sound and "feel" when it turns over as it always had, so I don't believe there's any catastrophic compression loss. The vehicle just rolled over to 100K miles (100,041 to be exact). About a year ago I changed plugs, rotor, cap and fuel filter but it may well have the original wires, although their still supple and all ends are clean and corrosion-free.
If this is any clue, this wasn't a slow deteriation, it went from running perfectly to poop with one turn of the key. How can I test the MAF (short of purchasing a $15,000 tester?)or the output pressure on the fuel pump?
Thanks again. |
Paul T. Schram (Paulschram)
| | Posted on Monday, October 21, 2002 - 01:15 pm: |
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What makes you think it is the MAF sensor? Have you checked the diagnostic readout beneath the passenger seat? I don't trust them, but we might as well see what it says. I have yet to see a valid code thrown by a pre-96 Rover.
I'm not yet convinced it isn't something simple and cheap.
Fake disgust in voice on:
If you have 100,041 miles and have even the slightest hint of suspicion it might have the original plug wires, replace those damned plug wires with Magnecors and get back to us!
Fake disgust in voice off!
I have had the very same sort of symptoms from a bad coil wire. Fine on the way to school, dies while trying to drag race on the way home-very embarrassing.
Pull your plugs just to see if they have been firing consistently. I feel very strongly (if you hadn't noticed) that you have an ignition problem.
To test fuel pressure (don't do this without parental supervision and don't tell your insurance company or the EMTs I told you to do it this way) take your cheapie tire pressure gauge and put it on the schrader valve on the fuel rail. When finished, throw your tire gauge away, or use at own risk. I figure it's cheaper to buy a tire gauge than a fuel pressure gauge when you are looking for little more than presence/absence.
As for the MAF (which I'm absolutely certain it is not), their is a procedure in the ETM. |
bryan
| | Posted on Monday, October 21, 2002 - 01:19 pm: |
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Did you put an aftermarket rotor on? I had 2 go bad and cause similar problems. Also have you checked to see if any codes are registering? Start with the cheap stuff first, and hope it's not your MAF. You aren't by chance running an over-oiled K&N air filter are you? |
Eric Ratermann (Ericrat)
| | Posted on Monday, October 21, 2002 - 01:28 pm: |
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Output of the fuel pump is a simple gauge from Autozone, Sears, and such. $25.00?
I know a lot of people have, myself included, have had to replace fuel pumps.
Help me out here, the VSS measures RPM at the trans output? If it is idling poorly, and won't rev properly when standing still then the VSS shouldn't be a factor?
I suspect my VSS is going flaky too, but I only get the high speed shudders once a month or so.
Does cleaning the VSS actually help?
Eric |
Paul T. Schram (Paulschram)
| | Posted on Monday, October 21, 2002 - 01:40 pm: |
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Eric:
There is some question as to whether or not the VSS is helped by cleaning with contact cleaner. Probably can't hurt. From what I can find, the VSS is an optical encoder with an output that changes frequency in relation to vehicle speed, hence, cleaning it might not do you any good, but can't hurt.
I have not found a cheap fuel pressure gauge with a fitting that fits the Rover schrader valve and have found the cheapie tire gauge works just fine.
It could be fuel pump, but let us rule out the easy stuff first. |
Jim
| | Posted on Monday, October 21, 2002 - 02:42 pm: |
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I'll have the plugs out in a few minutes, will let you know how they look. Do I need to crank the motor when checking the fuel pressure or is having the key turned on good enough with an electric fuel pump?
As far as the on-board diagnostic readout, I've snooped at that unit but don't know how to read it or make it talk (sorry, I'm a little stupid), what's the secret?
I'm totally with you on the plug wires and will replace them but, the way it failed on me (it won't even start now) it seems there would have to have been at least 4 that failed all at once.
With all deference to an ignition problem, I'm looking first at fuel. They way its "wanting" to fire when I turn it over is very much like its starving for fuel. |
Jim
| | Posted on Monday, October 21, 2002 - 02:53 pm: |
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(Jim again) fuel pressure is 34 lbs according to my cheapie tire guage (thanks for that tip, worked beautifully),
The book show spec to be 2.4 bars so that's about right isn't it? (roughly 15 lbs per bar, or am I wrong?)
Plugs comin' out next.
Thanks all, will be right back |
Paul T. Schram (Paulschram)
| | Posted on Monday, October 21, 2002 - 02:53 pm: |
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Jim:
Just turn the key on, the fuel system will pressurize.
Any chance your timing has changed? Mine did the exact same thing, drove to lunch, after work, no dice. Turned out one of the screws holding the vacuum advance can had backed out pulling the contact plate with it.
If you have a code showing on the diagnostic readout, you will be able to read it through the cover. Turn key on, look at unit.
As for four failing at once, you may have been limping along on seven and when the seventh one quit, so did your engine.
Paul |
Brian (Rover_Wannabe)
| | Posted on Monday, October 21, 2002 - 03:45 pm: |
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Or as said before it could be the single coil wire that crapped out. |
Jeff Price
| | Posted on Monday, October 21, 2002 - 04:27 pm: |
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I will apply computer geek troubleshooting. Check the last thing you messed with before it stopped working. In this case it sounds like the VSS is the last thing. I don't know what contact cleaner would do to a reed switch, perhaps not good things. Try unplugging the VSS and see if it makes any difference in starting and slight accel (sitting still in the driveway). or just swap in a new one. If that doesn't help then you have a more "interesting" problem.
cheers
-jeff |
Paul T. Schram (Paulschram)
| | Posted on Monday, October 21, 2002 - 04:51 pm: |
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Jeff:
Is the VSS a reed switch with rotating magnet or an optical source with a chopper in between source and sensor?
You're right, contact cleaner probably wouldn't do much with a reed switch. Maybe it's a Hall Effect like the crank position sensor.
Paul |
Jim
| | Posted on Tuesday, October 22, 2002 - 03:47 pm: |
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(Jim again) Note to self: Always listen to Paul T. Schram.
Even though I knew it wouldn't help I figured it couldn't hurt so I replaced the wires, plugs, cap and rotor.
Each piece by itself didn't look all that bad but apparently all together they produced a Land Rover that ran like crap.
Thank you Paul T. Schram! I shall never again fore-go the basics!
And for my penance:
I will perform routine maintenance
I will perform routine maintenance
I will perform routine maintenance
I will perform routine maintenance
I will perform routine maintenance
I will perform routine maintenance
I will perform routine maintenance
I will perform routine maintenance |
Paul T. Schram (Paulschram)
| | Posted on Tuesday, October 22, 2002 - 03:57 pm: |
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Vindication is mine!!!
Jim,
I'm glad I was able to help and hope I wasn't too forceful with my rant.
I have had so many situations where supposedly knowledgeable folks have said to go to the dealer for a testbook session, only for me to find it was a mechanical problem, requiring heavy tools, rather than an oscilloscope and Voltmeter.
Repeat after me: These trucks are very simple to work on and fix. Repeat as necessary.
With maintenance, dollars, affection and the occasional barked knuckle, they will run forever and take you to the ends of the world.
Peace,
Paul |
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