Greetings,

I have a 93 extended cab 4x4 pickup with the 3vze 3.0 v6 and a 5 speed manual. I have just recently completed a full rebuild of the engine using the DNJ master rebuild kit, with an Aisin timing belt kit, and had the heads machined and a valve job done. I put new Denso spark plugs, NGK wires, a new PCV valve, new OEM knock sensor and wiring harness, and all new vacuum lines. I checked the resistance of the pickup coils in the distributor, and made sure the bearings are good. I checked my TPS and made sure it is properly adjusted. I also checked all of my VSVs to make sure the relays worked, and that they held/released vacuum. I also checked/cleaned my EGR valve, and the PAIR valve. Since the build I have checked my cylinder compression and it is all good.

The problem is, the truck has no power, and you can feel a hesitation when accelerating. If you hold the throttle around 1500 RPM you can hear it missing, and I have tried to isolate the miss to a particular cylinder, but can't. My fuel mileage seems to be better than before though. Last tank I got 20.4 mpg.

I just checked my fuel pressure at the CSI, and had around 42 psi at idle, and about 51 psi with the throttle open. Is that too much fuel pressure?

Any suggestions would be greatly appreciated. This truck is just about to make me lose my mind. If I have left out any information I apologize. Don't hesitate to ask for more info if you need it.

Thanks in advance.

 

I don't have my book in front of me but that fuel pressure seems wrong, what does your book say?

How is your air filter, fuel filter, and fuel volume returning to the tank?

How is the ignition system, good solid grounds, signal lines all intact and firm, spark plug gaps good (did you check, somebodyight have dropped them etc.)

Describe misfire? No, late, or back fire? Is it burbling in the exhaust because it's getting much fuel?

How confident do you feel about your valve timing?

 

I don't have a FSM, just a Haynes manual. Everything I have seen said 38-44 psi, but a friend of mine said that fuel pressure being too high wouldn't cause the issues I am having. Not sure if that is right.

Air filter is new, and fuel filter has less than 8000 miles on it. What is the best way to check fuel return to the tank?

I set the gap on all the plugs before install. All the grounds should be good. What signal lines are you referring to? I tried replacing the distributor cap and rotor button with an Intermotor (from Advance Auto), but it made no difference, so I put my original Denso back on.

The misfire is not one particular cylinder, I can not isolate it. It does pop in the exhaust when the truck is holding back. Kind of like an old truck with a carburetor.

I forgot to mention in the original post, but the timing is set at 10 degrees BTDC. But the mark jumps around. That is with the E1 and TE1 terminals jumpered. You can tell that the mark stays on 10 the most, but it jumps up and down about 3 degrees in both directions. The timing belt I put on did not have marks on the belt, but my original did, so I counted teeth on the belt several times and then marked my new belt. After install I turned the crank two revolutions and all the marks lined up.

I have replaced the 02 sensor and the coolant temperature sensor. I also removed the catalytic converter (which had already had a pipe run through it).

Thanks again.

 

Your initial ignition timing should be rock solid with the test jumper in place, check for play in the distributor rotors shaft and that non of the electrical pickup coils are able to shift. All should be very solid. I would normally suggest checking the high tension (spark) cables aren't wrapping around or too close to the signal wires but you say it's consistent at 3° fluctuations.

It's possible for the pulley to separate from the rubber which causes the timing marks to shift, but they pretty consistently move backwards (eventually wind back up at. So this seems unlikely.

Over pressure in the fuel line leads to over fueling, which should eventually throw a code when it learns it's at its trim limit.

That popping burbling noise could be from either or both of these issues. It's raw unburnt fuel ignition inside the exhaust, given enough fuel it will become the typical "bang" most people call a "backfire".

I suggest and I would tackle the ignition timing issue first, then worry about the AFR.

 

Fuel pressure with just the pump running on jumper (no engine vacuum) is 38-44psi. http://web.archive.org/web/201003261...87fuelpump.pdf
At idle, 33-37psi. If you are getting 42psi at idle, you're running 13-32% too rich (and I'm surprised you're not getting a code 26).

I'm not as certain as co_94_pu that the ignition timing should be "rock solid" at idle. But +/-3° is a little too much. co_94_pu's advice (check for play, etc.) is correct and easy to do.

One common cause of excessive fuel pressure is a blocked return line. Replace the return line at the FPR with 6mm (1/4") vinyl hose to a suitable container. Run the fuel pump with the jumper. You should get about 1/2 liter per minute, but what you're interested in is the fuel pressure. If it drops back to 38-44psi returning the fuel to a "bucket" (atmospheric pressure), then you probably have a blockage somewhere in the fuel return line.

 

Thanks for your reply.

There is no side to side play in the shaft, just what I would call a small amount if tooth slop. You can twist the shaft maybe an eighth of an inch back and forth. I checked all of the resistance of the pickups coils and they checked right. How do I check them for movement? Take the cover off that is under the rotor button? I purchased a new distributor from RockAuto but the gear was mounted improperly on the shaft, and the pickup coils tested out of range, so I returned it.

Thanks again for your help!

 

Thanks for the information! I will give this a try as soon as I can. I'm a truck driver, so my time to work on this truck is kind of spread out.

So if there is no blockage in the fuel return line, is the next logical step to replace the FPR? If so, is there a particular brand y'all recommend?

 

Make sure the vacuum line that services the regulator is not plugged up as that was the case on my 91 4Runner. The metal line was choked up with corrosion and the suction from the VSV could not get to the diaphragm on the regulator so the rail was always over pressured and the injectors were having trouble delivering the right amount of fuel with over pressure in the fuel rail. When that regulator is working properly the fuel pressure in the rail fluctuates but far less than when it is not regulating the pressure.

 

The function of the regulator is to provide a constant fuel pressure ACROSS the injector. So as the pressure changes in the intake manifold (step on the gas => intake manifold VACUUM drops/pressure increases), the fuel pressure changes. This is why the spec fuel pressure is about 7psi different between not-running and idle (idle pulls about 7psi / 14inhg of vacuum).

So the fuel pressure is supposed to fluctuate, but in a commanded manner.

You probably understand this, but I couldn't quite get it out of the quote.

 

I have attached a picture of my distributor, can you tell me if what I have circled are the three pick up coil contacts? If so, none of them move at all. I don't see how you get the black cover off that says "Don't Remove" without removing that gear that the rotor button screws to. Maybe I don't need to, but I'm not sure how to inspect ant further. When checking the air gap, you are only looking at the contact that aligns with the teeth on that gear, correct?

Thanks again!

 

Here's the section of the manual that you need: http://web.archive.org/web/201212070...12onvehicl.pdf

While you don't want the coils to move at all, "play" is usually in the distributor shaft (if at all). You should be able to push the reluctor ("the gear") back and forth without any movement. A small amount of backlash ("twisting") is normal.