matts
Body Damage is Cool
Reged: 01/04/02
Posts: 1611
Loc: S.E. Wisconsin
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Diagnosing The 3VZE
I have a poor running 3vze. It starts like a champ, but it is very weak under load. Under load it is barely even responsive to the throttle until fully warmed up. With no load though it sounds alright. The main diagnostic points are:
1. Low vacuum: 12 " at idle or any steady rpm.
2. uneven compression: #1=170 psi, #2= 140 psi, #3= 170 psi, #4= 160 psi, #5= 175 psi, #6= 160 psi
3. diagnostic code #25 (lean fuel condition)
I have done the following:
1. new cap & rotor
2. checked timing: 12 deg. btdc
3. tested spark plug/coil wires: range 3k ohms - 16k ohms
4. compression test. (see list above)
5. spark plugs: look newer, light tan
6. checked air flow meter (AFM): ohms ok at specified points, air temp sensor ok
7. checked and adjusted throttle body
8. checked and adjusted throttle position sensor (TPS)
9. checked for vacuum leaks: looked for disconnected hoses, I blocked suspect vac lines to test for leaks down stream, eg.,PCV, Brake Booster, etc.
10. tested EGR: EGR not leaking vacuum.
I was getting a reading of 15" of vac at idle until I worked on the throttle body. I found that the throttle valve was cracked open a small amount because of maladjustment at the stop screw. I backed off the screw until the throttle valve was fully closed. Then I adjusted the TPS to the specified settings. After that my manifold vac was running around 12"! I also checked for vacuum leaks by spraying starting fluid (ether) around major vacuum and intake hoses and under the intake plenum. I am able to bring the vac up a few inches by advancing the timing to the maximum allowed by the adjusting slot on the distributor base, but that gets it to something like 30 deg, btdc!
This engine has 180k miles and had a head gasket job just before I bought it. The job was done by students at the local high school vo-tech shop. The only thing I found obviously wrong with the work on the engine so far is the throttle valve adjustment issue. The 140 psi cylinder reading is troubling, but I don't if it explains the low vac reading. A bad intake valve could screw up the manifold vac, but I think I'd see the needle on vac gauge jumping around a bit if that was the case.
Another reason for low vacuum can be valve timing, so I'm thinking maybe the lads at the high school may have gotten one of the cams a tooth off on the timing belt. Maybe that even explains the fact that all of the driver's side cylinders (except #2) are reading uniformly lower compression than the passenger side cylinders. Anyway, I'm eager to read what other troubleshooting, diagnostic minded yota brains think.
Here are some jobs I'm contemplating attacking next:
1. get the timing belt cover off to take a look at the cam timing.
2. do a cylinder leak-down test generally, and to check out #2, the cylinder with 140 psi compression.
3. pull off the intake plenum to redo all the intake gaskets
4. retorque the head bolts
5. check the valve clearances
6. test the fuel pressure
7. get the injectors rebuilt.
-- Matt
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'89 4runner SR5, 3.0, auto (fun)
'93 xtra cab, dlx,3.0, 5spd (work truck)
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stock87
Body Damage is Cool
Reged: 07/31/02
Posts: 1668
Loc: Placerville, CA
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My gut feelings:
The problem probably lies in numbers 5 thru 7 (second list), with #5 being most suspect to me. It's enough of a pain to do the valves on that motor I bet it's never been done.
That said, the leak down test would be the best next step in my mind, since it will tell you a lot before you go tearing into it too heavily.
Just my 2 cents.
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My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
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"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson
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kewlynx
Toyota & Classifieds Moderator
Reged: 10/06/02
Posts: 15756
Loc: Fairbanks, Alaska
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x2. Do the passive stuff before breaking out the wrenches. Looks like you've gotten most of it handled.
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http://www.walkablecommunities.org/
Democracy is two wolves and a lamb voting on what to have for dinner. Liberty is a well-armed lamb contesting the vote.
**ubi apis- ibi salus**
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matts
Body Damage is Cool
Reged: 01/04/02
Posts: 1611
Loc: S.E. Wisconsin
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Thanks you two for your input. I am headed over to Harbor Freight today to buy a leak-down tester. They have them on sale for $29.95!! I should have gotten a leak-down tester long ago. I'd like to build one myself with quality components but time is now pressing so I'm going to go with the inexpensive Chinese item. Also looking at picking up a fuel pressure tester like this one, but maybe that's a good candidate for a homemade job. Anyway I need to get this 4runner sorted out sooner rather than later. -- Matt
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'89 4runner SR5, 3.0, auto (fun)
'93 xtra cab, dlx,3.0, 5spd (work truck)
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Adam F
Forum Moderator
Reged: 01/29/01
Posts: 11592
Loc: Cincinnati, OH
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I'm going to say its timing or ECU related, either due to incorrect cam/crank timing, or bad ECU/TPS/AFM. 140psi in once cylinder vs 160-175psi in the others isn't going to make the truck run like you stated. Sounds VERY much like a bad spark or mis-timed spark.
I recently had a VERY similar problem with a 429CI v8 gas engine in a 97 Ford F700 truck. It started great, feathered the throttle and it would rev up fine, but if you put it in gear and drive, or if you just mash the gas, it would not want to do anything and sometimes spit and sputter. I swapped the ECU with another good working truck, and problem solved.
Do you have anyone near you with a similar truck? Anyone here on the board near you? Start swapping parts between the two until you find out whats wrong. Start with the ECU. Heck, I bet you could find one for free right here on the boards, along with probably most all of the other parts.
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88 4R, 350 V8, R150 5 speed Sold 
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride
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Snowtoy
Roll Me Over
Reged: 04/10/02
Posts: 3545
Loc: Grass Valley, CA
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I also doubt that the low comp on one cyl. would have that effect as well. I had a stuck exhaust valve, and only noticed a reduce in mileage and a slow down n climbing hills, other than that the engine ran fine.
Have you checked the intake tube for cracks.
Given the mileage of the engine it would be a good idea to have the injectors cleaned and rebuilt, they could be your problem as well.
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More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed
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matts
Body Damage is Cool
Reged: 01/04/02
Posts: 1611
Loc: S.E. Wisconsin
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Adam: You are scaring me with this talk of ECU problems, but I'll put it on my list of things to check.
Snowtoy: I found a small crack in the intake hose right at the throttle body; fixed it with 3M weatherstrip adhesive; no noticeable improvement. I still have basic things to check so I'll keep working my way down the list. The steady low vacuum holds the key I think.
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'89 4runner SR5, 3.0, auto (fun)
'93 xtra cab, dlx,3.0, 5spd (work truck)
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Adam F
Forum Moderator
Reged: 01/29/01
Posts: 11592
Loc: Cincinnati, OH
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Plugged muffler or cat converter could cause low vacuum. Unhook the exhaust before the cat and see how it runs.
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88 4R, 350 V8, R150 5 speed Sold
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride
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matts
Body Damage is Cool
Reged: 01/04/02
Posts: 1611
Loc: S.E. Wisconsin
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I actually saw the inside of the cat a couple of weeks ago when I was putting on a new head pipe. From the engine side it looked perfect.
Now I'm suspecting fuel issues are at the heart of my problem. I suspect bad injectors or O2 sensor. There may be a minor valve problem at #2 as well, but I think it's secondary. I'm gonna send off my extra set of injectors to WitchHunter Performance for cleaning and flow testing, swap out my O2 sensor for a used one that I know works, and do a fuel pressure test(probably in reverse order of how I listed it here). -- Matt
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'89 4runner SR5, 3.0, auto (fun)
'93 xtra cab, dlx,3.0, 5spd (work truck)
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Adam F
Forum Moderator
Reged: 01/29/01
Posts: 11592
Loc: Cincinnati, OH
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Half of my injectors were 60-80% clogged on my 3vze. It missed pretty good on idle, but ran better at full throttle. DIddnt act anything like your describing.
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88 4R, 350 V8, R150 5 speed Sold
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride
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