The truck:<BR>`87 2.6L, engine rebuilt 2 years ago. Original owner, good records.<P>Symptoms:<BR>Gas milage steadily dropping over the past 2-3 months and is now down 25%.<BR>Slightly rough idle, set at ~1100 rpm.<BR>Restaring when the motor's warm gives a 2000 rpm idle, The choke's back on.<BR>Burned through 3 L of oil very quickly recently.<BR>Recent onset of power loss when driving at steady throttle position for more than a few minutes.<P>Recent work (newest to oldest):<BR>Replaced automatic transmission mount, replaced fuel tank, install rear locker, high-flow exhaust with new cat, electric fuel pump, replaced vacuum controller, rebuilt engine, <P>Recent "events":<BR>While in a rock field on the Rubicon, and with too much oil in the engine, the truck landed hard on the frame and stalled the engine. After that it wouldn't idle properly, and I had to keep the rpm's @ 2000 or it would stall under load. I removed the excess oil, but had to adjust the idle up to ~1500 to compensate. This eventually cleared up after 3 tanks of gas with carb cleaner in them, and a lot of freeway driving. I brought the idle back down to ~1100, but it remained rough.<P><BR>What it's doing now:<BR>Driving at steady throttle (2000 - 3000 rpm for more than 2 minutes) results in a steady power loss (like fighting a worsening head-wind, or hillclimb). More throttle seems to exaggerate the problem. Downshifting sometimes clears the problem, and allows the RPM's to climb. Trying to push through the power loss with more throttle causes a severe engine power loss, followed by a brief couple of back-fires, and a fierce valve chatter session. Easing off the throttle, rather than trying to push through the onset of power loss, will usually let the motor run smooth again (though still powerless). In neutral or 1st gear (low load) the engine will easily run up to 5000 rpm.<P>What it FEELS like, and what I've done in the past week:<BR>Seemed like a sticking carb valve, or gummed carb. I sprayed carb cleaner into the throats, but didn't help much. The throats looked dirty. A bottle of Techron in the tank seemed to help, the problem onset was delayed, with less back-fire and less valve chatter. <BR>Brought it to the mechanic (a friend, who did the rebuild), and he figured fuel starvation. Checked the fuel filter (slightly plugged, replaced), the fuel pump delivery rate (OK), the vacuum on the secondary (seemed ok), the O2 sensor (watched it on the scope, OK), test drove with the vacuum gauge still on, and vacuum seems OK, test drive seemed better without the air filter, which still LOOKS ok. Can't seem to locate a reason. The exhaust's untouched by the Rubicon, and shows no marks (though it's cracked at the collector pipe from engine shake, hence the transmission mount replacement).<P>He then did the following:<BR>With the airfilter/holder off, he ran the engine to full throttle, then put the palm of his hand over the carb throats untill it nearly stalled the engine. He then repeated this rev/stall cycle a few times. He claims this can help clean out the carb. Afterwards the idle was noticable smoother than it had been for months, and so he adjusted the idle back down to ~950, and adjusted the mixture screw with the help of an exhaust gas meter.<BR>The problem SEEMED solved (Tuesday).<P>Went through the smog test (open hood, dyno) with excellent results on Wednesday.<P>Later that evening, after refilling the gas tank (WITHOUT any carb cleaner added) the power loss/backfire/valve chatter returned with a vengence. Though the idle is still smooth...<P>Can anyone offer a suggestion or 2?<BR>I searched the postings for carb problems, and I'm still a little stumped.<BR>It LOOKs like a depression chamber complaint, or a timing chain problem, or even a temperature sensor problem (which might explain my warm engine high idle), but seems like a gummed carb... All four? <P>Thanks,<P>Don<p>[ 22 November 2001: Message edited by: don ]

Sounds to me like the catylatic converter is plugged. My Dad had a doge d50 with a 2.0 and had a lot of the same symptoms you are having. A new cat and it was fixed. However I would remove the oxygen sensor and inspect it for fouling do to the oil situation you spoke of. You may try cleaning it if dirty or just replacing it (~$50). Possibly on the con the exhaust pipe or cat where crimped. Good luck

That is what it look like, a clogged converter. Also did you try new spark plugs? sometimes misfires are indication of lack of spark. Get some new NGK's and a new rotor, which should help considerably. I had the same problem some time ago where I had to downshift even on a light steep on the highway, T got new spark plugs, rotor. Also check this out, I went for new ACCEL spark plug wires but they at the autopart they didn't have them in stock at the moment [img]images/icons/mad.gif" border="0[/img], so they were going to order them for $25.00 and some change but BOOM!!! [img]images/icons/grin.gif" border="0[/img] I had a better idea, I grabbed a set of wires for an 8cil. for also $25.00 and now I have a spare set of wires for the same price [img]images/icons/cool.gif" border="0[/img]<P><B>JAVYPRO</B>

Wow don, sounds just like what I'm going through with my Nissan PU right now. I have put on new plugs, wires, dist cap, and fuel filter. Tomorrow I'm going to get another fuel pump from a junk yard and see if that is a solution. I've been thinking the carb needs to be rebuilt and I'm trying these things out of wishful thinking.<P>I haven't thought of an O2 sensor or cat though. I'll look into those.<P>Keep us advised on what it is.

Update:<BR>When I got home from work I pulled off the airfilter with the engine off and looked down the carb throats and the secondary was closed (should be), then turned the throttle mechanism to full open, and saw a good squirt of gas in the primary. At this point I could manually push the secondary open with a long screwdriver (good, it's not stuck). Put a longer vacuum hose on the depression chamber so that I could use my mouth to pull a vacuum on it, and the secondary opened and held vacuum reasonably well. Looks like the secondary's ok. Tried pulling a vacuum on the distributer, and it advanced and held very well. So that's OK. Ran the engine with one vacuum hose off, and the idle was rough. Replaced the vacuum line and the idle went smooth again. Looks like the vacuum's OK. Checked for suction at the reed valve, that was OK.<BR>Sprayed some more carb cleaner down the throat just to feel like I'm doing something. Then started the engine, and looked down the throats, manually pulled the throttle to wide open, and used my mouth to pull a vacuum on the secondary. Wow, did THAT ever rev that engine! OK, so it wasn't a smart thing to do...<BR>Put it all back together, and took it for a run. It seemed better. Perhaps the secondary valve is just sticking, even though the vacuum's good, and the action's good.<BR>So I put another bottle of carb cleaner in, and went out on the hiway. Noticably better with the carb cleaner. It still gets bouts of power loss, but infrequently, and usually after extended driving with the throttle in the same position.<P>I doubt the cat's blocked, or oil fouled. It's only ~8 months old, and tested excellent on the shop's analyser on Tuesday, and the goverment's smog test on Wednesday. The entire exhaust is a custom job, tucked outa sight beside the frame. There are NO marks on it from the Rubicon, and it's quite open.<BR>The fuel pump tested OK, and it's an electric pump at the tank. The Oxygen sensor tested OK, I watched it's signal on the FLUKE meter, and it cycles nicely.<P>When i tested the dist vacuum advance, I noticed that the dist cap and rotor aren't too clean looking inside anymore, so I should probably replace them.<BR>I'm asuming backfiring in my situation is from too much fuel (or more specifically not enough air). But the valve chatter? I wonder if my oil pump is not working properly, and that the hydraulic lifters are suffering?<P>Questions, questions, questions.<P>Answers?<P>(Mitch, I went through a list similar to this about 18 months back, and it turned out to be an inadequate aftermarket mechanical fuel pump that had been installed recently. The mechanic tested cat and O2 sensor as well by simply unscrewing the O2 sensor and going fo a test drive. Apparently the O2 sensor's hole is big enough to act as an exhaust system bypass.)<p>[ 22 November 2001: Message edited by: don ]

Don; <BR>Lets be careful here. When raw(read unburnt) fuel goes through the motor and into the exhaust system - there are some dangers.<BR>1. the unburnt fuel can dilute the engine oil and result in loss of the lubrication qualities that the oil has. (lifter noise??)<BR>2. Unburnt fuel will overheat the cat. and DESTROY IT in short order.<P>Now - is this something that has been very subtle for some time and now is noticeable enough so that it becomes a concern ??.<P>Some things that no-one has brought up yet and are VERY IMPORTANT.<P>1. The coolant temp sensor that the engine control computer uses to sense engine temp.<P>2. The throttle position sensor that gives the computer an indication of load on the engine as well as throttle opening and the rate of throttle movement.<P>These two sensors ARE critical to operation of the motor and also have the highest failure rate because of a constant temp change/ and constant throttle un-put changes.<P>Check out these suckers!!!!!!!!! I have repaired the TPS sensor - when I checked on that one it was $186.00 USD. my cost!!<BR>The coolant sensor should only be $ 20.00 to 40.00 USD or perhaps less.<P>Also be aware of constantly using a cleaner in the gas will contaminate the engine oil.<BR>Let me know what you find.<BR>Good luck<BR>Kary

Kary,<P>Thanks for the input.<P>The problem came on fairly quickly, about 2-3 weeks ago. I noticed a valve chatter for a few days, then the oil pressure dropped. Since the rebuild, the truck just doesn't burn any oil, so I hadn't checked it for the past 6 weeks. I added the oil back, and shortly after that the "sticking valve" behavior began. Prior to that it was just a slightly rough idle, since the Rubicon. The idle's smooth now. The "sticking valve" behavior can be intermittant, and avoided by using 2nd gear in the city. <BR>I'm wondering if I've got some floating crap in the carb inards, or even a blocked venturi port which is interfering with the secondary.<BR>I'll change the oil and filter, and the dist cap and rotor, and then try another hiway run to see if that helps...<P>Thanks...<P>Don

Big Blue<BR> I allways engoy your postings, you do know about everything [img]images/icons/smile.gif" border="0[/img] Hey, how did you fixed the TPS. Mine does not keep idle when the A/C is on. [img]images/icons/mad.gif" border="0[/img] Thanks [img]images/icons/grin.gif" border="0[/img]

Check the hard fuel lines along the frame for any dents and crimping. Drain the fuel tank next time it's near empty and check for crud. Pull the fuel pickup/fuel gauge unit from the tank and check the strainer on the pickup for clogging. Pull the carb upper cover and check for crud in the bowl, and reset float height. Problem sounds somewhat like one I had where I had crud intermittently blocking jets, vents, and bleeds in a carb. Tear down and cleaning solved it. Mikuni is not hard to tear down on the bench, but a b*tch on the mani.

Changed the oil and filter, and the distributor cap and rotor. Took a hiway drive.<BR>Runs REALLY smooth under no load.<P>BUT... <BR>When trying to accelerate from ~30mph in 3rd gear (A/T), ~2250 RPM, it sometimes just don't wanna go (it's about 50% of the time).<BR>1st and 2nd are fine, I can run up to almost 60 mph in 2nd (@5000 RPM [img]images/icons/smile.gif" border="0[/img] ) with little effort. It really does want to accelerate in low gears.<BR>Noticed:<BR>When trying a slow accelerate in 3rd or 4th (O/D) from ~2500 RPM, ~50% of the time a valve chatter begins softly, as soon as the throttle is advanced even the slightest amount. Whenever this happens, any more throttle results in that power loss, and a much louder valve chatter.<BR>If the faint chatter doesn't occur, then subsequent acceleration is normal.<P>Does this mean I have an oil pump problem, and that the autolash adjusters can't cope?<P>Eddy,<BR>I'll check the tank when it's low. The fuel pump's flow rate checked out OK, but maybe it's a floaty bit that's intermittant. I'll check the fuel lines and the exhaust again tomorrow. I'll put it up on a ramp, and really check it out. I'm hoping to NOT need to pull the carb for a cleaning, but it may be a good idea soon...<P>Kary,<BR>I had a temp sensor fail on me ~10 years ago, and I noticed it because one of the under hood relays kept chattering. I'll see if I can get it checked out. The TPS sounds scary, but I'll keep that on the list for the mechanic to check next week, along with the oil pump.<BR>I'm thinking of installing a vacuum gauge, and watching it for a while while driving, especially when the chatter begins. I may need a more accurate (responsive) oil pressure gauge as well...<P>Thanks all, and any input is appreciated!<P>Don<p>[ 24 November 2001: Message edited by: don ]