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Surging on acceleration.

Posted By: Trailmonkey

Surging on acceleration. - 04/14/21 11:19 PM

Just started this and getting worse the more I drive it.
Stop at the store and it drove fine, get back in and start it up, seems the idle is a bit off but ok.
As I take off it almost feels as if the trans is slipping or its cold, give it more throttle and not much happens, got upto maybe 40mph and bam it hits warp speed and is clear, I had it at about 45-50% throttle when it gets back to normal.
Doesnt do it all the time but when it does its after it was shut off and restarted.

Throttle position sensor ?
Idle control unit ?
Or possessed ?
Posted By: Mudraider

Re: Surging on acceleration. - 04/15/21 04:43 PM

Well, if you clean the MAF with a spray chemical, make sure it's Mitsubishi safe.
Posted By: Trailmonkey

Re: Surging on acceleration. - 04/15/21 05:39 PM

So you think thats the cause ?
The air flow sensor at the air filter looked good the last I seen it.
Posted By: Trailmonkey

Re: Surging on acceleration. - 04/16/21 08:56 PM

What ever it is, it does it for a short time then totally clears up.
Makes me think one of the two, the ones on the throttle itself.
Would the Idle Control Unit make it so as you give it some throttle input it has the ability to give a lower perceived throttle, fluctuate (surge) then opps my bad go back to normal ?
Or the Throttle Position Sensor simply malfunctioning for a bit then goes back to normal ?
After that its fine. Shut it off and it may or may not do it again.

I actually thought the trans may be slipping till this last time, and had the throttle opened up a good bit and when it cleared up jumped and took off as I had the pedal down more than normal. No slipping, thats throttle related.. hmmm

So now I'm asking the Montero Gods of Knowledge... is it my rear taillight bulb is out or one of the 2 mentioned culprits ? Haha
Posted By: Lev_from_CA

Re: Surging on acceleration. - 04/20/21 12:11 AM

Stumbling/surges sound like fuel issues. Old or watered down fuel, a clogged up fuel filter/in-tank strainer or failing pressure regulator. A failing fuel pump may also cause stumbles/surges if it's struggling to keep up with pressure demands, although that tends to be most noticeable at higher RPM.
Posted By: Trailmonkey

Re: Surging on acceleration. - 04/20/21 04:38 PM

And after about 15 seconds totally clears up...
In park I reved the motor up to 2000 rpm, ran like crap, low power and wanting to go up and down in rpm.. not changing the throttle input any it all of a sudden clears up and i had to let off the throttle to keep it from going over 4000 rpm, ran just fine after that.
Posted By: Trailmonkey

Re: Surging on acceleration. - 04/20/21 04:40 PM

Been getting about 13 mpg also.
Posted By: Lev_from_CA

Re: Surging on acceleration. - 04/20/21 06:19 PM

Yep, IAC could be acting as a vacuum leak causing the low RPM stumbling and hunting. Low fuel mileage and stumbling at low rpm/at startup could also be a plugged up fuel filter that the fuel pump takes a while to build pressure through. I suppose a failing FIAV can also appear as a vacuum leak, but that seems less likely in your case (stumbling while both warm and cold idle).

To check if the IAC is implicated, you can steer lock to lock while parked and watch how RPM reacts, it should increase matching the smoothness of your steering (steer quickly, RPM should rise quickly, steer slowly, RPM should rise slower). I remember you had AC removed, but steering exertion should also trigger the IAC to compensate for increased load. If you have a multimeter, you can check the resistance of the coils and measure the switching frequency during operation (iirc, 25-35 counts at idle, 65+ counts with AC/steering on). To test the IAC while warm, you can take it out, warm it up with a hair drier/heat gun (be conservative), and then test the coil resistance again.
Posted By: Trailmonkey

Re: Surging on acceleration. - 04/20/21 07:17 PM

Mudraider said to just unplug the Idle control unit all together and set idle with the stop screw. I'll do that and replace the TPS..
Fuel filter has less than 500 miles on it but not checked the pump yet. But its evident its been replaced or at least looked at as the little hatch has been taken off and reinstalled at some point.

Just odd how it clears up and starts working. I know these dont get the best fuel mileage but it should be getting at least 15+.
Just in case I'll replace the O2 sensor just so I know its fresh.
Posted By: Trailmonkey

Re: Surging on acceleration. - 04/22/21 04:59 PM

Simply unplugging the Idle control unit fixed the problem.
Set the idle screw till she idles at about 800 rpm, put it in gear and goes down to about 600 rpm or so the tachometer says.
The numbers sounds low to me but it has alot better idle quality and idles lower, has a more responsive throttle and is a bit more peppy.
Just feels better, I'll bet it will get better mpg now also. I hope.
Posted By: Trailmonkey

Re: Surging on acceleration. - 06/06/21 11:45 PM

Spray cleaned the MAF and it ran great, check engine light wanted to stay off even, but it's back at it again and can't get a can of that stuff anywhere.
Gonna get a remanufactured unit tomorrow and see if that is actually the problem, but as good as it ran after a shot of spray I'd say it is.

Thanks guys.
Posted By: Trailmonkey

Re: Surging on acceleration. - 06/11/21 05:42 AM

Damn, she runs soooooo much better. Lol
Remanufactured Mitsubishi MAF sensor unit from O'Reilly's did the trick.
Gonna plug the Idle control back in and see if It was even a problem, seemed to do better when I first unplugged it, but not so sure it had anything to do with it.
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/21/21 09:53 PM

Well thought all was good but NOT.. still doing it, but at times never totally clears up, I'm really thinking FPR.. got a new one, will install it when I replace the hydraulic valve lash adjuster on the front pass side, hoping to fix that damn tapping lol.
I may even pull the injectors and check/clean..

Fuel pump seems good, new filter. Pulled and checked catalytic converter and it looked good, pulled muffler and it was all rusted inside, swapped it out with a 2008 Crown Vic cop car muffler, sounds very nice now. So no exhaust blockage.
Anything as in timing that could cause this ? The distributor's inner disc looks clean under the dust cover so I left it alone.
Seems to me it has to be something with the fuel pressure regulator or throttle body ?
Posted By: rxinhed

Re: Surging on acceleration. - 07/22/21 03:32 AM

Have you examined the electromagnets and timing advance weights (if any)?
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/22/21 03:49 AM

Doesn't have any, has an optical reader that counts slots in a rotating disc, ecu advances/retards timing.
Posted By: Lev_from_CA

Re: Surging on acceleration. - 07/22/21 04:21 PM

Have you confirmed mechanical timing? Is the harmonic balancer/crank pulley wobbling? If so, then the crank pulley bolt may have gotten loose (or was not tightened to spec during last timing belt job) and wollered out the woodruff key slot that aligns the timing gear with the crankshaft. This can cause weird runnability concerns some times (I'm dealing with this on a 2002 Montero Sport with a 6g72 right now). The hydraulic timing belt tensioner is also known to fail if run far past its service interval.

The work to fix it, depending on how much damage was done, is:
  • get down to the crankshaft; similar amount of disassembly as a timing belt job, so this is a good time to think about a full timing kit refresh (also, crankshaft and camshaft seals)
  • clean up the key slot; iirc Loctite 660 or other similar retaining compounds can take up to about 0.5mm of lost tolerance here (the Miata guys have a long, storied history with this repair; "Pine Hollow Auto Diagnostics" on Youtube repaired a Montero Sport with a wollered out key slot by mig-welding it, but he is a more courageous/skilled man than most)
  • replace the woodruff key with a new one; original Mitsu is great, but the keys are a standard metric size that you should be able to find non-model specific options for (use caliper to figure out necessary dimensions)
  • replace crankshaft pulley bolt and washer with new updated part (these were recalled, iirc your year also).
  • reassemble everything:
    • chase all threads (threaded holes and bolts, both), blow out all blind holes with compressed air
    • use plenty of loctite (some people use high-strength red for the cranky bolt, but medium-strength blue is safer, since it doesn't need heat to be removed)
    • follow all torque specs (quadruple check these), for the crankshaft pulley I'd suggest just getting the pulley holder tool (or weld up your own), the torque spec really matters here (i.e. don't use the strap wrench method).


Edit: My bad, your version of the 6g72 seems to use a manually-adjustable pulley-style tensioner (# MD104578). However, this poses the same woodruff key/cranky bolt concern.
PS: a wire thread about balancer wobble, cranky bolts, woodruff keys (and a cameo of a 91 3.0), good read: /1076052/crank-pulley-wobble-with-new-pulley-and-tight-bolt-98-montero.html


Attached File
91-6g72.png  (1 downloads)
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/23/21 12:36 AM

This engine has about 1000 miles on it, reman unit, no I have not check mechanical timing as it has and does run perfect, then glitches.. did not do this when I first got it.
I'm getting ready to replace the front 2 HVLA on passenger side and the TPS, while its that far ill replace the pressure regulator, clean the throttle body and valves and what ever else is hooked to it, pull and clean and check injectors.
If it still does it ill replace the distributor and start checking wiring.
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/23/21 11:01 PM

Seems the first hour of driving it does it and clears up, but after everything gets totally heat soaked it never really clears up, as if what ever this is gets worse after totally warmed up. I'm gonna check for a code tomorrow but this is driving me crazy... well more so than normal.
Posted By: Mudraider

Re: Surging on acceleration. - 07/25/21 02:44 PM

Does it have a code showing? When mine did that, I did the JBfP electric tune-up. Basically, disassembly of the connectors and hitting each wire/connector with a soldering iron, make sure the wire itself wasn't loose in the terminal. Tedious, but it solved all kinds of weird maladies that mine had when I first got it.
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/25/21 11:46 PM

Not checked for code yet. Been hot as Satan's nut sak, I've unhooked the fuel line and cut it on and just checked that it shot a stream, but if the fuel pump is somehow acting up would it cause something like this ?

I did notice when it's running right its alot quieter of an exhaust tone, when acting up sounds alot deeper tone like if the packing blowed out of a glass pack. Lol

Before I put on the new pressure regulator I'll also get a new pump, ill find out what it is one day, just wish I had some help around here that knew about these.

As for wiring connections, I've called myself looking, wiggling wires and have only noticed some connection covers are dry and cracked, but the plug and wire under it looks OK. But I will start check these more, as with all those relays under the dash, like did they try and use as many as they could or what ?
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/26/21 12:05 AM

OK sun setting and it's cooled off.

Got 3 codes.

#1 Oxygen Sensor.
#2 Crank Angle Sensor.
#3 Fuel Pump.

I will check connections on all 3 first, but #1-#3 are replacement stuff, but the crank angle sensor.. is it meaning the optical reader in the distributor ? Or a sensor at the front of the crank ? I'm looking it up..
Posted By: Trailmonkey

Re: Surging on acceleration. - 07/26/21 01:22 AM

Was just reading a bad crank sensor can cause a lack of power to the fuel pump ?
You guys remember I had alot of my ignition go out, ecu, coil, igniter.. may have messed up the crank sensor as well ? On this model (1990) it says optical reader that reads the slots in the rotating disc. I looked and didn't see signs of water or dirt so I left it be.
Posted By: Mudraider

Re: Surging on acceleration. - 08/06/21 01:48 PM

Originally Posted by Trailmonkey


As for wiring connections, I've called myself looking, wiggling wires and have only noticed some connection covers are dry and cracked, but the plug and wire under it looks OK. But I will start check these more, as with all those relays under the dash, like did they try and use as many as they could or what ?



Lol. Electrical connections aren't a visual thing. You are using the Manual. Check out the Electrical FSM, you'll find a section at the beginning that tells about disassembly and messing with the terminals. Your trucks problems are intermittent and all over the board. Signs of lack of electrical signal getting to the computer. Good luck.
Posted By: Trailmonkey

Re: Surging on acceleration. - 08/07/21 04:17 PM

Originally Posted by Mudraider
Originally Posted by Trailmonkey


As for wiring connections, I've called myself looking, wiggling wires and have only noticed some connection covers are dry and cracked, but the plug and wire under it looks OK. But I will start check these more, as with all those relays under the dash, like did they try and use as many as they could or what ?



Lol. Electrical connections aren't a visual thing. You are using the Manual. Check out the Electrical FSM, you'll find a section at the beginning that tells about disassembly and messing with the terminals. Your trucks problems are intermittent and all over the board. Signs of lack of electrical signal getting to the computer. Good luck.



That's where I was reading that the crank position sensor (distributor) can cause bad ecu signals and therefore swings of voltage to the fuel pump and may also mess with timing advance...
I'll put the new distributor in and see if I need a new fuel pump or not.

And yeah when it cools down I will check connections for voltage..
Thanks MudRaider, hope to meet you one day..
Posted By: Trailmonkey

Re: Surging on acceleration. - 08/13/21 03:32 AM

Not going to say it's fixed this time till I drive it more, new distributor installed, timing set to as close to 5* as I could with the plug on firewall grounded, plugged the idle control unit back up and it seems to be running right, it did do it again after I installed the new distributor but the timing was way off, hasn't done it so far now.
Posted By: Trailmonkey

Re: Surging on acceleration. - 08/21/21 04:03 PM

About to go and put a timing light on it and wait for it to start messing up again and see if it's the timing going crazy that causing the problem. If so is there anything other than the distributor and ecu that would make the timing fluctuate ?
I replaced the distributor and nothing changed, so a bad ecu ? Stupid me can't find the receipt for it so the chance of taking it back is very low, It a freshly reman unit. I even took the relay apart and checked, all looked new inside, fine sand papered the contacts and it's still acting up.

Update later.
Posted By: Trailmonkey

Re: Surging on acceleration. - 08/22/21 02:48 AM

Timing stayed true as it idled and started running bad. Awesome.
Checked the FPR and unplugged the vacuum line and capped the nipple on manifold and it idled perfect and not once stumbled. Took it for a short test drive and had hardly and take off power but ran fine, so I'm 95% sure I've found my issue. I've got a new one already so we will see what happens when I replace it.
Fuel pump has been replaced before I got the truck so I think that's good as well as the filter.
Let's hope this is it.
Posted By: Trailmonkey

Re: Surging on acceleration. - 08/24/21 05:26 PM

New pressure regulator, ran great at first, only when it completely warmed up (over 40 min of driving) it did it again.
I will replace fuel pump just to make sure, but is there a water temp sensor that tells the ecu to act differently and not the dummy light.
The deal on the TB that has the coolant lines and the idle valve. Could it be the issue or would that only effect idle ?
I've unplugged the idle adjustment motor before and nothing really changed.

By the way, after sitting for 30+ min the fuel rail still had lots of pressure, so that tells me I don't have a leaking injectors right ?
After running a while and take gas cap off there is no pressure so that's good.

When it acts up it acts like spark or injectors are cutting out and all over the place as in how bad it is, at idle it starts, studders, then almost dies only to pep back up, driving it ends up never clearing up, acts like fuel starvation, or spark being erratic, I've unplugged many things and checked and don't see bad or dirty wires, wiggled as many as I could see and nothing.
Would a failing O2 sensor cause it ? Guess I can atleast take it out and look at it.
If it wasn't so short I'd be pulling my hair out.
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/04/21 12:59 AM

Ends up.. it's the injectors. How many not sure but I got 6 reman Bosh units on the way. Along with a new O2 sensor just because.
Posted By: Oso

Re: Surging on acceleration. - 09/06/21 04:09 AM

Do yourself a favor and inspect the entire wiring harness- especially the spark plug wires and injector harness. Mitsu wire is prone to cracking - especially after 30 years in a hot engine compartment. Mostly you'll find the cracking near connectors. Cracks on the outside usual mean a mostly broken wire inside.

Remove your grounds and clean them well. Get em shiny. Then soak the harness connectors in vinegar overnight to get them clean. displace the moisture by blasting them out with electrical contact cleaner.

Bad injectors don't cause intermittent issues, rather, they are regular and predictable. Bad electrical signal that has to overcome resistance or broken strands in the wire will be intermittent.

But i'm just reiterating what Mudraider already told you. The problem is electrical,

HTH
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/06/21 11:10 PM

Just can't seem to find the problem is my problem, check the plugs and surrounding wires, voltage readings, but for sure an injector was cutting out, checked spark and it was fine, it's either the injector or electrical to the injector, I will be removing the TB, Plenum and replacing the front passenger side HVLA.. while it's in that state I'll replace the injectors, check all wires and lines.
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/08/21 12:08 AM

Still getting code for fuel pump, replaced it and filter just recently.

But says crank angle sensor again also, I know the wiring could be bad but the previous owner did put 30 year old parts back on after replacing the engine.

None of this started till the deal with most of my ignition system and ECU took a dump on me.

Where on the front of the engine is the plug for the CAS ? What's the best way to check it, says nothing about it in this pos Hayne's manual.

I need to get an actual factory manual and go over as many wires as I can and check..
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/08/21 12:15 AM

Wow, could just be the wiring or sensor itself, but after reading this, sounds alot like the problems I've been having.

https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-crankshaft-position-sensor
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/08/21 02:59 PM

I have 5 out of 7 issues stated in that article.
I will check the wiring and connections but I've found alot of wired that are brown in color, none that's green with corrosion, just brown. I will clean the one for the CAS first and work from there.
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/09/21 08:45 PM

I mean, mine has one right ? Every time I pull one up on ebay, amazon or any parts store website it says won't fit listed vehicle.
Posted By: rxinhed

Re: Surging on acceleration. - 09/10/21 02:26 AM

Yeah, no CAS or CPS on this model. It's very rudimentary. Have you checked the air gap in the dizzy? Have you verified one of the magnets has not cracked?
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/10/21 03:14 PM

Best I can tell the distributor uses an optical pickup, not a magnetic. I pulled the other one apart to see if I could find what was wrong with it, couldn't see anything and turned it in as a core for a remanufactured factory unit, truck still get code .. so it has to be a wire, same for the fuel pump, still getting code for it and had just replaced it along with a new filter.

Does the voltage get reduced to the pump at times like idle or is it full time 12v ?
I'm thinking running my own ignition triggered relay directly to it, I mean it has the Fuel Pressure Regulator.

As for the distributor, I'll start looking and testing wires, but does the wires from the distributor go directly to the ECU ? That way I can color code them and check, bypass if needed.
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/10/21 04:28 PM

Now if I can find the fuel pump relay I'd check it first. But the only photos I can find are for the Sport or newer models. I assume it's by the ECU/MPI relay or behind the glove box..
ECU/MPI relay checked out fine.

Where would the best place be to get an ignition on only hot wire to trigger a relay if I end up bypassing the factory setup ?

Thanks guys. I know I'm a pain, but it's hard to explain my problems and get answers that I need, been hoping it wasn't a wiring problem as that's not my strong point, but as many have stated it more and more looking that way.
I need OldColt here, he likes wires hahaha
Posted By: Trailmonkey

Re: Surging on acceleration. - 09/11/21 12:01 AM

Best I can see in wiring diagram fuel pump doesn't have a relay.
Wire tests coming soon.
Posted By: Trailmonkey

Re: Surging on acceleration. - 10/03/21 07:13 PM

Found out it was the wire from the O2 sensor plug up beside the transmission, and a bad coolant temp sensor.

Wire fixed the bad stumble but it ran awesome till it warmed up, ran like crap and engine bay was hot, new coolant temp sensor and it runs very nice now..
Posted By: Trailmonkey

Re: Surging on acceleration. - 10/12/21 11:34 PM

I think I may have the wrong or bad water temp sensor.
Runs awesome when first started and warms up, but after everything heat soaks (30 min or driving) it lacks power and seems to heat the exhaust up as the temp gauge stays normal.

Reading how the ecu changes the a/f ratio as the temp goes up, could it be like the choke it stuck on a carburetor engine ?
Or more likely the air valve under the TB the water lines go to ?
I've unplugged the other air valve and nothing changes.

Seems I've got it just about right but when actually driving it longer I still have this problem.

I assume the JB-Weld and or block off plate for the TB is what I'm going to try.
Been talked about before but I "think" the block off plate for the car will fit the montero ?

Also.. could I splice in a rheostat into the water temperature sensor and tell the ecu what I want and what runs the best at the time ? I don't think I got the right sensor, same plug but could be a different ohm ..
Factory supposed to be 2.5k cold and 290 hot.. from what my manual says.
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