| Author | Message | ||
     John Cronin (Jec) New Member Username: Jec Post Number: 22 Registered: 02-2003 |
95 Disco, 86,000 miles. Just replaced a cracked right exhaust manifold this weekend (had to replace a cracked left manifold 15,000 miles ago), then found the downpipe was cracked and took it to a local shop, who took off the pipe and welded it up. After driving home from the shop (it's a climb from 4,000 feet to 8,500 feet), the garage filled with smoke. I just figured it was the oil on the new manifold burning off. Today, it smelled hot again when I got home, so I looked and noticed the bottom part of the manifold and the flange on the downpipe were glowing red! Talked to the muffler shop, and they suggested possibly bad oxygen sensors or clogged cats. But, no check engine light, no change in gas mileage, no change in power. Called the dealer (200 miles away!), and they suggested it may just be that the oil burning off the manifold made it hot enough to glow. Said they rarely replaced O2 sensors for mileage (even though they know mine are due), and said if the cat was clogged we should have noticed the loss of power. They suggest another trip up the hill to see if it's still glowing, which I will do. Anyone else ever experienced this, or have any thoughts on what the problem might be? Thanks in advance. John | ||
| Carl D. (Cdoug3) Member Username: Cdoug3 Post Number: 45 Registered: 01-2003 |
The manifold on the discovery should be no where near hot enough to glow! I would say there may be something blocking the exhaust or maybe the truck is running lean. Oil burning off of the manifold surely shouldnt cause it to glow. I have had the exhaust on my Audi hot enough to glow but that is after really running the shit out of it and the egt's are already much hotter than the disco. | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 23 Registered: 02-2003 |
Carl: Wouldn't climbing 4,500 ft in 17 miles at 50-60 mph (which is our drive home)qualify as running the Disco hard? The dealer mechanics, who are at 5,000 ft, said they have seen Discos there that supposedly have no problems "almost running red," after climbing the nearby hills, and said they think that at least the early Discos did not do a good job of maintaining mixture at high altitude, and therefore were not surprised. Maybe I'm naive, but since they didn't tell me to call a tow truck and rush our truck in for new sensors, cats, and whatever else, I tend to believe them. Shouldn't we have seen a change in mileage or performance with lean running or a block in the system? Thanks for your reply. John | ||
| Jason T. Barker (Speedminded) Member Username: Speedminded Post Number: 195 Registered: 10-2002 |
got pictures? | ||
| Geoff 93 RRC (Geoff) Member Username: Geoff Post Number: 66 Registered: 11-2002 |
Are you using premium gas? Regular runs hotter. | ||
| Ron L (Ronl) New Member Username: Ronl Post Number: 17 Registered: 11-2002 |
this ussually happens when there is a serious timming problem and/or running very lean. I put money on it running lean since you got it up to speed. | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 24 Registered: 02-2003 |
yes, using premium. Am I correct that if the O2 sensors fail the system defaults to a "rich" condition? If so, what could be happening to cause the mixture to lean out? I'm going to check the timing tomorrow to be sure on it. John | ||
| Bill Bettridge (Billb) Senior Member Username: Billb Post Number: 733 Registered: 02-2002 |
lean - lean -lean - you'll smoke a valve very soon if it's actually running that hot. Bill | ||
| todd slater (Toddslater) Senior Member Username: Toddslater Post Number: 267 Registered: 08-2002 |
Lean or partially blocked cat. If both manifolds are glowing ....I'd lean more towards ...well...lean. (but still wouldn't rule out cats). If it is just one side, check the cat on the glowing side. | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 25 Registered: 02-2003 |
Todd: how does one go about checking the cat? I checked the timing, and it's okay. Plugs look the same on both the right and left bank: white on the tip, but black and sooty (not oily) at the end of the threads. I'd interpret that as a combination of signs for lean and rich, so I would think they're okay. I've got a set of O2 sensors on order from Nathan for good measure. Beyond the sensors, any ideas on what would drive the whole system to run lean? Thanks, John | ||
| todd slater (Toddslater) Senior Member Username: Toddslater Post Number: 268 Registered: 08-2002 |
John, Here is a link to a very good and fairly concise how to write up. www.babcox.com/editorial/bf/bf19922.htm | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 26 Registered: 02-2003 |
Todd: Thanks, that is very helpful. Meanwhile, today's drive revealed that it is BOTH manifolds, so we'll whittle away at it. Spoke with the dealer mechanic, and he thinks we are puching the truck too hard up the hill, rather than having a problem, so tomorrow's test will be to go a little lighter on the throttle and see what color the manifolds are when we get home. Thanks again, John | ||
| Scott Scott (Scottoz) New Member Username: Scottoz Post Number: 29 Registered: 02-2003 |
I think its a thing of beauty | ||
| todd slater (Toddslater) Senior Member Username: Toddslater Post Number: 269 Registered: 08-2002 |
John, When you pull your plugs, what is the color/condition of the insulators. Normal is light brown greyish brown. If the insulators are a blistered white, it is an indication of a lean mixture. | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 27 Registered: 02-2003 |
Todd: Definitely not brown. Insulator is greyish on one side, white (but I wouldn't describe them as blistered) on the other. Checked two plugs from each bank - all very similar. Much as I'd like to think otherwise, I guess I'd have to conclude they look lean. Dealer suggested checking the fuel pressure (in addition to changing the O2 sensors)if the plugs looked lean, so I'll track down a guage and check it out. John | ||
| Keith Kreutzer (Revor) Member Username: Revor Post Number: 184 Registered: 11-2002 |
Red manifolds.... Lean ..... Red cats.... Rich.... | ||
| Geoff 93 RRC (Geoff) Member Username: Geoff Post Number: 69 Registered: 11-2002 |
How's the fuel pressure? Is the fuel filter newish? Clogged injectors would restrict fuel flow also. Buy a bottle of Techron. Also, are you keeping the revs up (above 3K) on the hill? Higher rpm's move more air through the engine which helps control temps. Might be a bad factory fuel map for that altitude/load. | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 28 Registered: 02-2003 |
Geoff: Need to get a guage next time I'm in town to check pressure. Filter has 11K on it. I'll try the Techron. Yes, always drop it into 2nd to keep revs above 3K on the steep part of the hill. Thanks, John | ||
| Carl D. (Cdoug3) Member Username: Cdoug3 Post Number: 46 Registered: 01-2003 |
Actually Higher revs = Higher EGT's | ||
| Justin (Vanroth) New Member Username: Vanroth Post Number: 15 Registered: 02-2003 |
Higher load = Higher EGT's | ||
| cdoug (Cdoug) New Member Username: Cdoug Post Number: 1 Registered: 04-2003 |
Both will lead to higher EGT's, typically you will have higher load if you have higher sustained engine speed | ||
| Ron Brown (Ron) Member Username: Ron Post Number: 247 Registered: 04-2001 |
Something is screwed up. Is is a GEMS or dizzy truck? If it is an early truck check the timing first. Badly out of time trucks will do exactly what you describe. As far as checking cats and O2s if you have a GEMS truck have the dealer or someplace with rovacom do realtime monitoring to see how the O2s and cats are performing. It takes a LOT to have an O2 or cat throw a code. Ron | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 30 Registered: 02-2003 |
Ron: Thanks. It's a dizzy truck (95), and timing is right on at 6 degrees. No rovacoms in town, and 4 hours to the dealer. Am also going to try the carb cleaner air leak test (but when the truck is cool, NOT glowing). The thing that keeps bothering me is that it drives with the same amount of power it has always had, even up the 8% grade at 8,000 feet. Seems like most of the potential causes would degrade performance. John | ||
| Ron Brown (Ron) Member Username: Ron Post Number: 248 Registered: 04-2001 |
humm, Could be a big vacuum leak. Check that, kind of a long shot though. A bad O2 could do the same thing as well as a bad MAF. With your truck you can't see as much as on a GEMS truck so the real time monitoring is not as usefull. If you are sure it is properly timed something else is causing it to run lean. If it were me I would unplug an O2 and put it in open loop and see if you have the same issue. I am willing to bet you do not which would lead me to suspect a sensor. Ron | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 31 Registered: 02-2003 |
Ron: I'll try unplugging one O2 sensor tomorrow and post back whether that cools off that side. Thanks. John | ||
| John Cronin (Jec) New Member Username: Jec Post Number: 32 Registered: 02-2003 |
Ron: While we're on the topic of sensors, do the fuel temp and engine coolant temp sensors have any control over mixture once the engine is warmed up, or do they only come into play at startup? Thanks John | ||
| Ron Brown (Ron) Member Username: Ron Post Number: 249 Registered: 04-2001 |
Pulling one O2 should cool off both sides, pull the plug not the whole sensor. It should throw a check engine light and should put the truck in open loop (which is a default setting which is, among other things, rich). As far as your second question I am not sure, but I kinda doubt they would have that kind of impact you are seeing. Ron |
