97 FZJ80 Stumbling off idle (1 Viewer)

[jjg]

My US fzj80 with about 220K is stumbling off idle. When I first start her up she will fast idle just fine for about 10 seconds or so and then when the fast idle drops she starts stumbling and barely running. If I try to depress the throttle she will stumble further and practically die. If I feather the throttle and play with it lightly sometimes I am able to increase the RPM above idle but even if I can get the RPM up above 2K she is still breaking up while up there.

Some background information, The car has been sitting for roughly a month while I did the oil pump seal. The oil pump seal was a bear and I had JIS bits breaking off in the screw heads (yoda should have used torx! ). The problem seems to have occurred upon the first startup after the oil pump job was complete. The truck was not perfect before I started the oil pump job. The truck would idle fine and run fine under light throttle conditions but break up if pushed hard. My plan was to stop the huge blood loss from the oil pump and then troubleshoot the WOT break up while I was using the truck daily. Alas now she will bearly idle.

So far I have:

1. Inspected all the vacuum lines and the intake rubber from the MAF to the plenum. No Visible leaks.
2. Shot starting fluid all around the intake/ vacuum lines and intake area from the MAF downstream. No change in idle.
3. Shot starting fluid straight into the air filter to see if that would make a difference in idle. Oddly it did not.
4. Inspected the wiring including the harness by the EGR. All looks good.
5. Disconnected and reconnected also wiggled various connectors to the distributor and other components to see if that would make a difference. It did not.
6. Pulled the EFI main relay in the fuse area on the driver's side inner fender while the car was running to see if that made a difference and the car immediately died.
7. Pinched the Vacuum line going the Fuel Pressure Regulator. No difference. Pinched the fuel return line from the FPR. No difference.
8. Removed the return line to the tank from the FPR and replaced it with clear tubing to a jerry can and started the engine. The fuel will flow out of the FPR at a moderate rate with some air bubbles in it.
9. Removed the Vacuum line from the FPR while the engine was running and clear tubing still connected. The fuel would stop flowing from the FPR indicating to me that the FPR is functioning properly and blocking all return fuel when Vacuum is not present. Again none of this made any difference to the way the truck runs.
10. Changed the hi-tension lead from the coil to the distributor cap which looked so so. No difference.
11. Changed the distributor cap and rotor. No difference.
12. Checked for codes. (I actually did this in the beginning but did not want to reorder my list PO300 Random/Multiple Cylinder Misfires detected. Then PO301, PO302, PO303, PO304, PO305, PO306 For Cylinder #1 through #6 Misfire detected respectively. (I said to myself No $hit Sherlock

My gut instinct from the very beginning is this is a fuel pressure issue but I don't see a way to check the pressure. The fuel pump is obviously working somewhat or else the car would not run at all. The fuel pressure regulator also seem to be working from my crude tests above but maybe the fuel pump is not making enough pressure?

With that said can anyone link me to a part that will go in between the FPR and the Fuel Rail with a schreader valve on it so I can put a standard fuel pressure gauge on the rail? Is there any other way I can test the fuel pump or drive it harder to see if that will solve my problem? just a FYI the fuel pump has already been replaced once on this truck when it had about 120K miles back in 2002 when the pump failed on me in New Hampshire at the Yankee Toys Fall Gathering.

Does anyone have any other suggestions as to where the problem may lie? My next steps to kill time while I wait for your response is to pull the plugs and take a look at them. I may even change the wires as I have a spare set on hand but I really doubt if all 6 wires could fail at once.

Thanks and regards,
John

 

[morganism]

Do the EGR valve tests. If EGR plugged open on a carbon rock, truck will not idle.

Quick repair method is to tap on the EGR valve top hat, while sucking on the vac line. That may drop the rock out, and you can hear it rattle down into oil pan.

You have to apply suction quickly and let off to keep it from stalling.

There are a couple VSVs and a VTS under the intake too i believe.

 

[jjg]

Thank you for you suggestion. The EGR cannot be the problem at this point in time. It was fixed so it can no longer cause any problems about 15K and 2 years ago when my son and I did the head gasket. I won't say any more about it.

 

[RoaringFork]

Quick repair method is to tap on the EGR valve top hat, while sucking on the vac line. That may drop the rock out, and you can hear it rattle down into oil pan

LOL... oil pan

@jonheld is right

Back to topic

 

[morganism]

Have you reset the " readiness monitor drive pattern" should be a link in the FAQ.

 

[bugsnbikes]

Check the harness near the ecu behind glovebox where it contacts/crosses the metal bracket.

 

[jjg]

Have you reset the " readiness monitor drive pattern" should be a link in the FAQ.

Are you referring to achieving ECU readiness after properly fixing the EGR? If so, I have the special readiness relay and resistors installed. I achieve readiness pretty quickly with them.

I will also look at the harness by the ECU. Thanks for the tips.

Now for some more questions. I found some info that says the fuel pump relay varies the speed in which the fuel pump runs. It has been my suspicion that the fuel pump is running but not hard enough. Can anyone go into more detail on under what conditions is the fuel pump driven at different levels? What controls it? I also saw something that says connect pin 3 from the relay to battery positive to bypass the relay and drive the fuel pump. Will that drive the fuel pump at maximum duty? If so I have in mind to just drive the pump via +12V as my next test.

Also, I am still searching for an adapter that will sit between the FPR and the fuel rail to allow me to get a fuel pressure gauge on the rail. Somebody must make one. Anyone know where? Seems like a great product for Wits end.

 

[jjg]

So I spend all day today working on the cruiser and at this point in time, she is running ok. Not great but drivable. Quite frankly, I don't know what I did to make a difference. I did alot. I pulled all the plugs and checked them. They all looked fine. I ohmed out all my plug wires and all are in spec under 19Kohm. I did a compression test. My numbers were not terrible and about what I would expect out of a 220K cruiser. While had the plugs pulled I decided to borescope the engine. The pistons fine albeit pretty black. I could read all of the lettering on the pistons and see the casting marks clearly. There were some areas of the piston that looked cleaner than others so I decided to do a hard decarb while I had the plugs out.

I use a product from the PB blaster company called "Lawn Mower Tuneup" They recently renamed it small engine tuneup. This product has worked wonders for me decarbing many of my outboard engines. I figured I'd give it a shot in the I6. I sprayed it into the plug holes and let it soak for a while. Then I fired it up with a huge cloud of smoke and continued to empty the rest of the can into the engine with through one of the plenum vacuum ports. It seems to have worked because of this the only thing that I could think of all the stuff I did that could have possibly made a difference.

I also rented a fuel pressure gauge from autozone. This gauge had the M12x1.25 banjo bolt adapter to tap into the output line of the fuel filter. With the gauge in hand I ran some tests and compared it to the specs I found here:

Fuel pressure gauge question

That thread was very helpful to me. Thank you Tredwards. My values were pretty darn similar to Tredwards after he did the new pump

this is what I had:
1) idling fuel pressure with FPR vacuum line hooked up is around 32
2) idling fuel pressure without FPR vacuum line connected is around 40
3) idling fuel pressure with return hose clamped is around 45

I could not achieve the 57psi called for in the manual unless I drove the pump with +12v directly to pin 3 of the Fuel pump relay harness.
When I drove the pump with +12v direct, my pressures were alot better. In fact I even hit 70PSI when driving the pump with +12v and clamping off the return line. I will also say that with 70psi of fuel pressure my throttle reponse was very sharp. The truck felt like it should and RPM would rise instantaneously upon hitting the throttle as it should.

At the end of the day when I put it all back together and returned everything to the way Yoda intended it, the truck was running but throttle response is still bad with a big hesitation when I hit the throttle from idle. If I feather the throttle lightly I can get her to run ok and she is driveable.

So with all that said, I am still at a loss to what is wrong. There is no smoking gun. The FPR and the pump do seem ok in my eyes. I checked all the harness and connectors again too. Nothing seems awry.

When you read this does anything seem out of place to you? Any other areas to check?

 

[jjg]

Update! Well, earlier today I thought the Decarb made the difference between drivable and not but what I found out a few hours later is that the only thing the decarb did was run the engine long enough to heat it up good and then it became drivable.
While I was typing my reply the truck was sitting and getting cold. When I got into the cruiser to take it for a ride a few hours later what I found is a truck that would barely idle and stumble horribly on any throttle input just like it had been doing since I finished the oil pump seal. This time, Instead of giving up on it as I did previously, I kept pushing it and it warmed up. Once it was good and warm it was drivable again.

It still has a heasitation but atleast it is drivable. So for all my efforts today, I have really no improvement. About the only thing I have to show for my efforts is the knowledge that truck improves enough to be driveable once it heats up.

What say ye?

 

[morganism]

Readiness monitor is in the 80 FAQ.

• TSB_EG003-02_(revised) 96-02 readiness monitor drive patterns.pdf
  
  
  Try running a ground wire from the coil hold down cage igniter to a solid ground, the 100 added one.
  
  If you blockd EGR port, did you leave the VSV and the VTV intact? Can they bleed into the system?
  
  

 

[ppc]

The 1FZ-FE has two engine temp sensors, one for the dash gauge and the other is input for the ECM. The one for the ECM could be your problem. Also I would test the fuel pump relay and resistor that switches the voltages powering the fuel pump. What happens if the stumbling occurs and you push the accelerator all the way down? Does the stumbling go away after a couple of seconds and the motor revs like it should?

 

[jjg]

Readiness monitor is in the 80 FAQ.

• TSB_EG003-02_(revised) 96-02 readiness monitor drive patterns.pdf
  
  
  Try running a ground wire from the coil hold down cage igniter to a solid ground, the 100 added one.
  
  If you blockd EGR port, did you leave the VSV and the VTV intact? Can they bleed into the system?
  

Morganism, I tried clicking the link but it did not work. I am assuming it just tells me that I would need to drive at a certain speed for a certain amount of time in a certain sequence or something like that to achieve readiness? I spent alot of time searching the board and researching stuff when the EGR was fixed and I remember something like that. But again, to fully properly fix the EGR you need to add the relay and resistors and then rediness becomes a non issue. As for the VSV and VTV (which I am not sure exactly what they are) yes they are still intact. Even the EGR is there too just fixed. I live in the people's republic of New Jersey so I am still subject to many emissions laws along with visual inspections. so yes, they are still there and I dont recall doing anything to modify thier operation so I guess they could bleed into the system. What problems would this cause and how do I check? I will add that ground wire.

The 1FZ-FE has two engine temp sensors, one for the dash gauge and the other is input for the ECM. The one for the ECM could be your problem.

Phil, I believe your onto something. I had the am thinking about the temp sensor for the ECU. The one for the gauge seems fine. Now if I could only find it along with the test procedure. I have the FSM. I will start digging.

Also I would test the fuel pump relay and resistor that switches the voltages powering the fuel pump.

Yes I would like to test those. Unfortunately, I don't know how. I don't know where is the resistor and the only way I know to test the relay is to bypass it. I have had a suspicion that the high setting of the relay is not coming into play when it should but again, I don't know the condition in which that will happen. I have been driving around with a mechanical Fuel pressure gauge taped to my windshield. I can tell you under no circumstances did I ever see my fuel pressure higher than 46 while driving and I even made some spirited runs to 4K in second gear once the engine was warmed up and I had gotten the engine past the hesitation zone.

What happens if the stumbling occurs and you push the accelerator all the way down? Does the stumbling go away after a couple of seconds and the motor revs like it should?

When it is stumbling it is breaking up and misfiring. I know this is harming the engine. I cannot bring myself to hold the throttle in this condition longer than a second.

 

[Tedward]

Fuel pump resistor is hiding on front passenger wheel well. Just behind the cruise control near the firewall.
I'm thinking a failed resistor will fail open. As in no voltage resistance to slow the fuel pump.

 

[ppc]

If the resistor failed completely (open circuit) then there would be no voltage to the fuel pump under the "light load" conditions when the relay switches the electrical path through the resistor. Bad connections may cause additional voltage drop to the pump. I believe the 97 model is setup and functions similar to the 94 model where the diagnostic port in the engine bay has the FP terminal where the voltage to the fuel pump can be monitored. Monitoring the voltage and fuel rail pressure together is going provide a lot of good information for problem solving.

The conditions where the relay switches are documented in the FSM but basically full voltage to the pump occurs at startup and under higher load conditions. With my 94 I found the voltage would not change under light acceleration but under moderate and high acceleration the voltage would switch in approximately two seconds. For that reason you you need to test the full open throttle for a longer period of time. That will not harm the engine.

 

[jjg]

Good Info Guys. I spent another day at it with few hours of the day with my head buried in the FSM. The fuel pressure resistor was tested and checked out. The FPR relay tested and checked out. The Coolant temp sensor checked out as monitored by the torque app and a Bluetooth ELM in the OBDII port. The TPS monitored and checked out also via Torque and ODBII. The VSV for fuel enrichment was not checked out but according to the FSM the VSV will only enrich under hot start conditions for the first 120 seconds after start so I am sure it is not my problem. At this point in time, I have a solid grasp on how the fuel system in the 1FZFE works. Enough of a grasp to realize if I want to drive the pump at full B+ voltage all of the time, all I need to do is put a simple jumper in the pins of the connector going to the fuel pressure resistor which I did. Alas,there is no joy in Mudville today. Nothing I did made a difference.

Tomorrow I want to check the timing of the truck. Does anyone have any good procedures for timing an 80?

 

[ppc]

Jumping across the resistor can be tried but that does not eliminate any impact of the relay. I would remove the relay instead and build a short jumper with a couple of spade connectors to plug into the connector to establish the bypass. My philosophy in testing/debugging is to eliminate as many legs of a circuit or as many components as possible in order to isolate and narrow the scope of a problem.

 

[jjg]

I thought eliminating that relay too Phil. It would have been real easy to hardwire +12v onto Pin 3 of the Fuel pressure relay and bypass everything. Then for sure I would have maximum voltage too..... But all those relays are there for a reason and one of those reasons is safety. this way I am driving the pump at the max voltage the circuits allow and I have eliminated the possibility of the resistor, or failure to go into high-pressure mode as the cause of my woe. Now if you can tell me what pins to check on that diagnostic port I will certainly monitor that voltage tomorrow to know how much voltage drop I am getting through all the relays and circuits.

 

[ppc]

As I stated in post #14 above it would be terminal FB to ground. Inside the cover of the Data Link Connector should be a legend.

 

[jonheld]

Try running a ground wire from the coil hold down cage igniter to a solid ground, the 100 added one.

I guess if you repeat this often enough, at some point you'll be right. Sort of like how a broken clock is right twice a day.

 

[jjg]

Thanks Phil for the refresher on the diagnostic port. I had forgotten about that many years ago. Its all starting to come back to me now. Jump the E1 and TE1 pins to set timing.... Ahhh, at one point in my life I knew these trucks pretty darn well. Unfortunately, my 97 does not have a pin in position FP to measure voltage just an empty socket. Also, unfortunately, With the E1 and TE1 pins jumped and the timing set back to 3BTDC I still have no joy just a big hesitation where I should have throttle response. For reference, my timing had been set to 6BTDC which is where it previously seemed to provide the best performance.

I am still at a loss guys and am running out of things to check. Some more info for you, Since I have been driving the car I have received the PO171 (system too lean bank 1) 2 times in succession. I put a Fuel pressure regulator on order from my local dealer just to give it a try even though my fuel pressure numbers seem inline with Tredwards above. I should have it Thursday. Sure hope I can get this fixed as I am leaving Friday morning for a hunting trip up in NYS. Opening day Rifle is Saturday and I need the truck.

I put some videos in the next post.