So the fiancee wants me to burn my Disco and buy a Ford Escort with the insurance money, and I must say I'm tempted, and a little confused myself about this.

Today I left from a camping/wheeling trip about 200 miles from home, and after ten miles (give or take), I began to have a severe loss of power and the engine started to miss. The miss sounds like a missing spark, and it sounds like it's coming from the back center area of my engine compartment. I know that the coil pack (for lack of a better phrase -- it's a 1996 so it's GEMS) is back there. I have brand-new spark plugs, and the original plug wires (108K).

Has anyone had this problem before? I literally can drive 59 mph without any problems -- shortly after hitting 60+ mph, it has the miss and loss of power. If the engine sits for a while it's fine again...as long as I don't exceed 59 mph. Low speed driving is fine too -- wheeled yesterday and Saturday with no problems whatsoever.

I'm thinking it's:

(1) Plug wires
(2) VSS (due to the very specific nature of the onset of the problem)
(3) "Coil pack" or whatever
(4) Valve problem (because it's always my biggest fear with this truck)

Thanks for the help -- I already searched but found nothing, and other sites are more interested in selling me their junk than in helping me fix my own junk... :flipoff2:

Andy

My first thought was Vacuum advance, until I read the GEMS part. Since it seems to be speed related, it very well might be the VSS. I think if you drive in 3rd as opposed to "Drive," the VSS isn't active, and that is a quick way to diagnose the issue, though I could be wrong on this. It certainly couldn't hurt to replace the wires, infact I would recommend doing this.... and coilpack, it's gonna go soon enough too. :flipoff2:

Andy,
My 97 is doing something similar, but the trigger for me is RPMs. I can drive or accelerate to 2900 RPMs with no problem, but 3000 causes what feels like a miss. So far, I have changed the fuel filter, plugs, wires, cleaned the MAF, used FI cleaner, etc., but it hasn't made a dent on my problem. I have a coilpack on the way to try it. If I figure mine out, I'll let you know (in case they are related) please do the same for me!

Thanks.

Andy,
My 97 is doing something similar, but the trigger for me is RPMs. I can drive or accelerate to 2900 RPMs with no problem, but 3000 causes what feels like a miss. So far, I have changed the fuel filter, plugs, wires, cleaned the MAF, used FI cleaner, etc., but it hasn't made a dent on my problem. I have a coilpack on the way to try it. If I figure mine out, I'll let you know (in case they are related) please do the same for me!

Thanks.

Dan,
Your issue sounds like it is a TPS issue.

Andy:
Throw a set of Magnecors on there (when were the plug wires last changed?). While you're at it, are the plug wires securely in their homes?

The speed sensor is a somewhat pricy part, let's change things that we know need changing before we spend $100.

(I'm betting it's the speed sensor)

Andy, with 108K on your original wires they are shot. I had had the same problem 97 disco and replacing the wires did the trick (twice). My2cents

[QUOTE=PTSchram]Dan,
Your issue sounds like it is a TPS issue.

Thanks, PT. I'll give it a shot. The TPS could be the culpret although it does not matter what gear I am in, etc?

Thanks! This is driving me nuts!

If the wires are original its your own fault the thing is acting up. Open the hood at night and look for 'leaking' voltage for the wires. Maybe mist some water around them to give them a conduit to leak. When you see the blue order some wires.

JP

Speed sensor should solve your issue..Very typical symptoms of a speed sensor gone south..

Speed sensor should solve your issue..Very typical symptoms of a speed sensor gone south..

I agree, but let's spend the $ where it is warranted. Until we return an engine to something of a baseline, replacing a more complex, more expensive and more reliable part is not indicated. Plug wires have a finite life, he hasn't replaced them in many, many miles-they are needed. If this doesn't solve the problem, then we can replace the VSS. The VSS might be bad, but while they are a common failure, not as common as failure of plug wires. Example, I had 203K miles on my VSS when I replaced it with one that only had 115K miles-it wasn't the problem, a muddy MAF sensor was :flipoff2:

Plug wires are on the way. Will update the class on results, e.g., whether VSS is bad as well.

Thanks for the help!

OK, so the truck sat all week with only minimal low-speed driving. This afternoon took it for a test spin on the highway to test (1) whether the miss would happen again and (2) whether driving in third gear would help indicate if VSS was malfunctioning.

After 20+ miles @ 65+ mph in 4th gear, no stumble/miss/anything. Damn truck purred like a kitten.

Am I correct in thinking it was the plug wires all along? Like, intermittent bad connection or something? Or is VSS not as bad as I feared?

Its the plug wires. Had same before. Most noticeable at low speeds in the bush. On highway at part throttle its not as bad.

In the meantime you are dumping unburned fuel in your oil and thinning it out. Better change that too.

Bump...so I drove to Black River Falls (approx. 3 1/2 hours) last Friday, and was humming along for about 45 minutes at 75mph with no problems, when the miss started up again.

Since last update I:


Replaced the stock wires with 8mm Magnecors (properly seated)
Changed the oil twice
Ran Seafoam through the intake


I drove another 3 hours at 60-65mph with no problems, wheeled all day Saturday and Sunday with no problems, and drove for about 2 hours home at 60-65mph with no problems. I have noticed the oil pressure idiot light at times, but I think that is an unrelated issue (leakage at the oil pan gasket) based on low oil level -- and that's being corrected.

However, I got within 55 minutes of home and the truck developed the stumble again. I got off the highway, parked, waited, and on restart the engine ran fine, so I decided to test the theory on VSS. I drove for about 8 miles at 65 or so in 3rd gear, and it stumbled and missed. I drove backroads at no more than 50-55 the rest of the way home with no problems. I read somewhere (here?) that the VSS won't malfunction in 3rd because it knows it can't go that fast in 3rd gear. I'm puzzled by this because the truck runs so great up to those speeds...and I was under the impression that the VSS caused a fault (and therefore a cylinder run-rich miss) that was corrected when the speed was corrected to an acceptable level.

Any ideas / suggestions / criticisms? :flipoff2:

Andy

my vote is still for throttle position sensor.

But why would the TPS be a problem at a given RPM level on the highway, in 3rd or 4th, but not on a trail, at the same RPM level? It's also not an intermittent, brief miss, which is corrected once the RPMs drop -- this is an increasingly violent miss that continues until the truck is shut off and sits for a few minutes.

Compression test next. What do the plugs look like? Can you get it on a scope to watch the ignition?

Plugs are brand new and clean.

Getting it on a scope is going to be difficult without going to the dealer.

Plugs are brand new and clean.

Getting it on a scope is going to be difficult without going to the dealer.


A good driveability independent can scope the DIS. What did the plugs that came out look like? Show us pictures of the plugs maybe.

JP

Plugs were (compared to a set of "diagnostic pictures" I have in my possession) basically OK. The truck briefly had the wrong plugs in it due to a combination of my trust in a parts-counter guy and the parts-counter guy not giving me the right part number. That was when this misfiring shit started -- those plugs came out before they'd been in very long, and were relatively normal looking. Those plugs were swapped out over a month ago and I tossed them in the parking lot of the Wal-Mat where I bought the correct plugs the day this started.

Another guy on another board suggested the coil pack might be going...and I'm starting to come down on either that or an injector problem. Am I in the ballpark?

VSS is cheaper than even a used coil pack.

But why would the TPS be a problem at a given RPM level on the highway, in 3rd or 4th, but not on a trail, at the same RPM level? It's also not an intermittent, brief miss, which is corrected once the RPMs drop -- this is an increasingly violent miss that continues until the truck is shut off and sits for a few minutes.
good point. This "wrong plug" issue is perplexing- the problem started after the new plugs went in, and will not go away with the correct ones? Injector issues should not be the result of that, hmm... unless you can awap parts with someone local with same truck, sounds like it needs to make a trip to the shop for scoping.

Yeah. I put in (IIRC -- at work right now) Autolite P34's, and needed P36. I hate it when the parts counter has the part I need behind it. The problem then reared its head while I was driving to Lake Geneva to meet Discosaurus for my "new' tires, and was a problem all the way back.

Plug wires got changed, with new/correct plugs preceding them. Truck does not miss at idle, or at city driving speeds. The miss, when it happens, gets worse with time, and seems to be related to vehicle speed (although still missing in the "put it in 3rd gear" test seems to exclude VSS -- right?). I was thinking leaky injector finally catching up at a certain speed, and causing a one-cylinder misfire, but I have no codes thrown.

It sounds like we had a vaguely similar experience. My experiences are chronicled below. But the saga ended with me replacing the bosch alternator with a chevy alternator, which cured the stumble in the first thread.

http://www.pirate4x4.com/forum/showthread.php?t=300311

and

http://www.pirate4x4.com/forum/showthread.php?t=308668

Also, there are better mechanics than me entertaining your spark plug theory, but I've never seen plugs cause an intermittent problem. Or, a residual problem after the correct ones have been reinstalled. That also wasn't cool to litter in the WalMart parking lot.

It didn't start right after that stoned Bimbo ran into the back of your truck, did it ??

LOL Forgot about that. No, it was actually doing it on the way to Lake G. :D

Uhh, any body think of buying the VSS, installing to see if it fixes the problem, and if not, clean it up and take back to dealer. Hell we did that in the shop at Rover all the time. And i still do it weather its pep boys or LR. Alot of times guess work and a few minutes can fix a problem alot faster.

PS, it is likely not your TPS. Unless you are describing the problems wrong
But, it could be you MAFS, any minor leak behind the MAFS can cause similar problems. As well as a flat out crapped out sensor

Uhh, any body think of buying the VSS, installing to see if it fixes the problem, and if not, clean it up and take back to dealer. Hell we did that in the shop at Rover all the time. And i still do it weather its pep boys or LR. Alot of times guess work and a few minutes can fix a problem alot faster.

PS, it is likely not your TPS. Unless you are describing the problems wrong
But, it could be you MAFS, any minor leak behind the MAFS can cause similar problems. As well as a flat out crapped out sensor

The man may be sniffing at your problem. Don't you have a good bud with the same truck you can borrow parts from to figure this out? MAF is an easy swap to check. I also agree your symptoms seem unreliable for diagnosis. The wrong plugs did not cause this only to not correct the issues with the correct plugs installed later.

Keep after it.
JP

Hey Prosqter,

I haven't been wheeling to Black River Falls in years. Not to hi jack the thread, but are some of the trails still open? I had heard this area was mostly, if not all shutdown to trucks, and only ATV's and horses had any trail use. Rick

You have PM.

It does occur to me that the MAF could be the culprit, as I removed the airbox and intake hose to get to the spark plugs and wires -- I guess there could be a leak of some sort that only becomes power-robbing at higher speeds? Is there any rational basis for this theory? I'll be checking MAF for obvious issues and intake hose tonight for leakage.

Also in favor of MAF issues...the first weekend I had problems I drove ~3 hours, wheeled, and only had trouble on the way back. We weren't in mud but it was awfully dusty and MAF has never been cleaned, so maybe it was the proverbial straw...

Shoulda bought a IIa. Then it's just leaks... :flipoff2:

Thanks for the help, guys...will update later, after I rip shit apart. :flipoff2:

OK, MAF sensor isn't too bad, although it's dusty. I did, however, find a rubber o-ring loose in the airbox. This o-ring fits perfectly over both ends of the MAF, and I am not sure which end it is supposed to be on. I am out of town and don't have my shop manual on me. This leads to to more questions:

(1) Does it go on the intake plenum end of the MAF, or the airbox end?
(2) Could something this simple lead to power loss?


Thanks again!

It goes on the airbox side. Doubtful it would cause the problem as they are often lost with no ill effects.

Did you ever try the SPEED SENSOR. I lost count how many people have told you that was the problem. Or are you just determined to prove us all wrong. Granted that may not be the problem, but it is the most likley.

Just a quick note I had similar problems. I fixed and tested as I applied a range of possible solutions. Cleaned the MAF with CRC contact cleaner, new wires, and new plugs. The solution of course was the last thing I did the plugs. Cylinder 5 and 7 the plugs were broken. I got an intermittent miss when they would pull apart due to vibration then they would fit together and start working again. Both plugs were cracked on the insulator and after looking I pulled at the crack in one and ended up with two pieces. Visually they looked fine except for the hair line crack.

Do I know that is what was wrong? No. OBD II codes said intermittent miss effecting the Catlaytic convertor. Did the plugs fix the problem? Yes. No miss since then 3000 miles or so in travel.

Did you ever try the SPEED SENSOR. I lost count how many people have told you that was the problem. Or are you just determined to prove us all wrong. Granted that may not be the problem, but it is the most likley.

(1) I'm a stubborn German kid :flipoff2:

(2) Waiting on a speed sensor, want to see if it's something simpler.

(1) I'm a stubborn German kid :flipoff2:

(2) Waiting on a speed sensor, want to see if it's something simpler.

Your gonna be waiting for along time, cause it does not get simpler than replacing the speed sensor. It will take about 5 min and only require the removal of 1 bolt. You can do it in the parking lot of your local rover dealer.

I seriously would rather replace a Speed sensor over changing plugs any day.

Your gonna be waiting for along time, cause it does not get simpler than replacing the speed sensor. It will take about 5 min and only require the removal of 1 bolt. You can do it in the parking lot of your local rover dealer.

I seriously would rather replace a Speed sensor over changing plugs any day.

One small bolt that's easy to get to once you're under the truck. I also think you need a speed sensor.