climbBC

Hi guys, I'm new here, but I've been searching the forums for some kind of clue or solution for my problem. Here's the situation: Tuesday of last week I spent probably a couple hours driving all over the place and the truck ran fine, like normal. Then I stopped for half an hour or so and when I jumped back in I had a dramatic loss of power. Hesitation while accelerating, low idle (usually idles at between 750 and 1000 rpm, right now it's closer to 500 and the whole truck vibrates more than usual), low power. It feels like it's not getting enough gas to me (but I'm still pretty new to the mechanical world). There's no smoke coming out of the tailpipe or anything, and the truck passed California smog less than two months ago so I don't think there could be anything wrong with the catalytic converter.

So I took it to a mechanic this last Monday and after a cursory look at the engine, he suggested spark plugs, EGR valve, and then took the oil filler cap off while idling and the engine sputtered down and sounded like it was going to stall. He put the cap back on and said it's a valve problem that's going to need the whole top end taken apart and sent to a machine shop. I thought that was a big jump to make, but I've never taken the oil filler cap off while idling before. Is that what's supposed to happen? I did some googling and got mixed responses ranging from "never take the oil filler cap off" to "if it stalls when you take the cap off it just means your engine is running correctly" and just about everything in between. So what do you guys think? I don't know anyone with the same kind of truck/engine as me so I can't try it myself.

Not being ready to just jump into a major overhaul by an unknown mechanic, I took the truck home and have been seeing what else the problem could be. So far I've checked the EGR valve (which responded to the vacuum pump the way the manual said it should), and done a compression check on the cylinders and put in new spark plugs just in case. The compression seems good enough, so I'm kind of sceptical of the mechanic's valve diagnosis since that should have been illustrated by the results. I'm sure a professional would be able to glean a little more out of the results than we could, but it seemed ok.

I've changed the fuel filter, the pcv valve, and checked the airflow meter (which measured up according to the Haynes manual). The oil pressure switch broke off while changing the fuel filter so I've been trying to find a replacement that fits the wire fitting (so far the one that broke off seems to be one of a kind) but that seems like a minor crisis compared to the drastic loss of power.

The engine still has low power starting out, feeling real sluggish, and then sometimes it'll act completely normal for a second (or after it's driving around 35mph in 3rd gear for a while sometimes the power feels like it should). But it's still not right, and sometimes I can't even get the truck up to 15 miles per hour with the gas floored in first or second.

I'm completely stumped. On Monday I made an appointment for tomorrow to have the compression checked by a second mechanic, so I'm going to get the truck over there somehow and see if they can figure out what the problem is. Anybody here have any ideas? thanks for reading all this if you did.

mightymouse

iTrader: (6)

First and foremost do not go back to that mechanic! There is a whole thread on this forum dedicated to the motor running weird after the oil cap is removed. It's just like creating a big vacum leak. So we've established the cap pulling and running funny validating a head rebuild to be a complete crock of crap. That is no way no how the right way to diagnose this. I delt with similiar issues on my 22re before so i'll list out a few cheap and not so cheap fixes. Check your intake tube for cracks and check your whole motor for vacum leaks. To do this get some carb cleaner and spray in specific areas to see if it changes the idle. If it changes the idle then eureka you found your vacum leak! Since you already put plugs in and hopefully you used ngk's or densos do the wires rotor, and cap as well. Check you timing while you're at it. I have also replaced my afm with the 1982 toyota supra afm and replaced and adjusted my tps as well. I myself have yet to use the seafoam product but there are many yotatechers that swear by it. Check you fuel pressure and make sure the fuel pump is operating properly. Also check your o2 sensor and wires i've heard that they can cause a truck to run crappy as well. When and if you get time 4crawler's site is a godsend and has helped me through many rough situations. Good luck hope someone else chimes in with some more ideas. You get my vote of confidence these little motors are actually easy to work on and most novice mechanics can fix whatever problems arise. Just sayin don't be afraid to dig into it there is a vast amount of knowledge on this site to fix just about everything on your truck.

climbBC

Thanks, mightymouse, I wasn't planning to go back to that mechanic so it's nice to have a better reason than a gut feeling. I'll start right in on your list of things to check in the morning. You said you changed your afm (that's the active fuel management, right?) with one from an '82 supra. Mind if I ask why? Was the stock one defective or is the supra's just superior? Just curious. I'll look into this seafoam product, as well (I'm learning all kinds of new things here). I take it you meant to spray the carb cleaner on the outside of the vacuum tubes to check for leaks, right? Also, could you send me a link to the thread you mentioned above? I've become rather curious about this whole oil cap business.

Thanks for the clarification. That does look more like the part I broke. (kinda wish it was the oil pressure switch, though... $10 vs $130)
I'll also try the TPS check. Thanks for noting the setting for KΩ and the picture, too.

Thanks for the quick replies! I'll let you know how things work out in the days to come.

rangerruck

now that it was mentioned, and i am no mech by the way, i vote egr valve. I had a 90 buick regal that had all the symptoms; sputtering , stammering, seemed like it was barely getting gas, ran real rough no power, etc. took it to one ... I say it through gritted teeth... mechanic, not my regular guy, but a place down the street. he pretty much ruined my car, still could not figure out the prob, and charged me 400 bucks for the crap work he did try, he had it about 2 weeks. took it to my regular guy, he fixed all the other guy's crap work, cut wires, etc., figured the egr valve, got the right replacement in 2 days( I have a squirrely model egr) and had it fixed in 3 days.
Sounds like egr, or vaccuum.

mightymouse

iTrader: (6)

AFM stands for air fuel meter or something similiar it's also referred to as the MAF or mass air flow meter. It's the part that connects to your filter and intake tube. As for the supra mod do a quik search on this site and you'll get a load of info on that one.Sorry just to clear that up! Good luck keep us posted!

mightymouse

iTrader: (6)

Oh here's the link it might not be helpful i haven't read the begining in a long time but the thread is good for a laugh.https://www.yotatech.com/forums/f5/2...-wierd-141477/

abecedarian

Check that none of your spark plug wires are chaffed and shorting out. Check the distributor cap and rotor, in particular that there are no signs of carbon tracking in the distributor cap.
Verify that all of the ducts / intake tract is tight and that the boots are flexible and have no cracks in them.
Make sure that all of the electrical connections are clean and tight, and none have any moisture / condensation.
You have a manual so also check the ignition coil and igniter too.

climbBC

The TPS responded smoothly to the Ohm-meter (between 0 and 2KΩ).
The ignition coil measured primary at less than 0Ω (analog meter can't show decimals too good) and secondary at 7KΩ (I think that's a couple KΩ lower than the specs).
Distributor cap and rotor looked clean, as do the plug wires (the boot on one plug is damaged, but I don't think that's new. I'll change that ASAP).
EGR checked out again.
Intake tube no cracks and tight.
The AFM met the manual specs the other day when I checked it.

I don't have any carb cleaner laying around, so didn't check the vacuum hoses for leaks.
None of the parts shops rent timing lights, and the fuel pressure gauge didn't have the right fitting to screw into my fuel filter.
I already had an appointment with the mechanic and I've run out of entire days I can spend elbow-deep in the engine wondering what's going on, so I took 'er in to let some professionals take a look and see what they can find. Haven't heard back about their diagnosis, but I'll keep y'all in the loop.

Thanks again for all the advice.

shaeff

^ You're not just looking at vacuum hoses for vacuum leaks, spray around the intake manifold where it mates to the head, at the joint of the upper and lower intake manifolds, around the throttlebody, and the powersteering idle up valve as well.

climbBC

I got my truck back from the shop today. Looks like it wasn't anything too serious, they cleaned the throttle body, adjusted the TPS, and adjusted the timing. I didn't have a chance to drive it very much today, but the drive back from the mechanic was just like it used do drive, about three- or four-hundred percent better than when I took it there on Thursday.

Thanks for your advice, you folks were right on with the diagnoses!