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Truck sounds like a popcorn maker!

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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Truck sounds like a popcorn maker!

Old 11-29-2018, 04:34 PM
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Truck sounds like a popcorn maker!

So lately I've noticed that my 86 pickup has been backfiring every now and again but not out the tailpipe it sounds to be in the headers, now fast forward a week and here we are I have lost a ton of power struggling to hold 40 going up a slight hill and at 3,000-3,500 rpm the truck is poping NONSTOP! I had a shop conduct a compression test and they said it came back good. I have also tested the injectors (brand new from LCE) and they came back to be functioning as they should, my next thought was possibley a clogged muffler so I unhooked it and the poping went away I think (REALLY loud and difficult to tell) and there was still no power any ideas? TPS mabe????

forgot to mention I have also checked the distributor cap, spark plugs and wires and the camshaft for possible flat spots but everything checks out
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Old 11-30-2018, 05:02 PM
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Update: just got done changing the fuel filter thinking it could possibly be clogged and that also made no diffrence. At 40mph the truck is screaming at 4200rpm and I am not gaining any speed, actually losing speed. I also tried unplugging the tps while it was running and the truck died so I'm assuming the tps is good next thought is a possibly bad ECU?

Last edited by Cumminsguy1; 11-30-2018 at 05:05 PM.
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Old 12-01-2018, 08:32 AM
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O2 sensors. I get trucks coming to me all the time with similar issues. I would say 75% of the time it is one or both of the 02 sensors. The truck tries to compensate for a faulty 02 and throws everything out of wack.
If not 02 related check the water level, grounds, clogged ERG or plugged CAT

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Old 12-01-2018, 09:22 AM
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Thanks for the reply. I checked the cat by unhooking the entire exhaust system at the bottom of the headders and it made no difference, one of the O2 sensors is located on the portion of the exhaust that was unhooked. I was not aware that there are 2 of them where is the other one located? And another UPDATE: today I opened the MAF sensor and played around with that and it seems to be working as it should so I'm ruling that out as well. I have also conducted my own compression tests just to make sure the mechanics were not BS.ing me and sure enough each cylinder came to 120 so I know compression is good

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Old 12-01-2018, 10:16 AM
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Auto or manual?
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Old 12-01-2018, 10:20 AM
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Originally Posted by ev13wt View Post
Auto or manual?
It's an Auto
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Old 12-01-2018, 11:55 AM
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Ok mabe it is the O2 sensor because it runs the same unplugged as it does while its plugged in. I just cant see it making this big of a impact and I hate to keep throwing money at this problem
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Old 12-01-2018, 03:28 PM
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Alright guys so here's where I'm at. I just got done replacing the O2 sensor and it made no difference so while I was on the side of the road I decided to pull the TPS connection off once again this time once I did the idol cleaned up and evened out nicely so I figured it wouldn't hurt anything to mess around with the TPS positions once I plugged it back in I begun to move it around. I've been able to get the idle set now however I still have no power. What do you all think? Time for new TPS?
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Old 12-02-2018, 06:43 AM
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Originally Posted by Cumminsguy1 View Post
It's an Auto
Was hoping for a slipping clutch :/

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Old 12-02-2018, 08:22 AM
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While the truck is running Jumper the computer as if you were going to set the timing. If the idle drops then the TPS is working. It may be out of spec. Get on 4cawlers site and dial it back in and see what's what.
While running wand a propane torch NOT LIGHTED around the intake and check for leaks.
Ive seen people throw all kinds of money at similar symptoms only to find out there was a crack in that big air hose that goes across the front of the motor from the MAF to the throttle body. Your issues don't sound fuel related, they sound vacuum related.

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Old 12-02-2018, 09:11 AM
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Originally Posted by toyospearo View Post
While the truck is running Jumper the computer as if you were going to set the timing. If the idle drops then the TPS is working. It may be out of spec. Get on 4cawlers site and dial it back in and see what's what.
While running wand a propane torch NOT LIGHTED around the intake and check for leaks.
Ive seen people throw all kinds of money at similar symptoms only to find out there was a crack in that big air hose that goes across the front of the motor from the MAF to the throttle body. Your issues don't sound fuel related, they sound vacuum related.
funny you brought up using a jumper last night I had a similar idea (went to see if I can pull a code but nothing) anyway when I plugged the jumper in the idle did not change. I'll go check the hose now for possible cracks but it looks to be in good shape. I got a TPS ordered from 22re Proformance and should be here in 2 days, really hope that's the issue because I have checked EVERYTHING!
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Old 12-02-2018, 09:51 AM
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Alright just got done checking for leaks in the pipe going to the MAF sensor and it's good, also double checked the PCV valve to make sure it's not clogged and it was also functioning as it should. I went ahead and started it up and drove it with the cold start injector unhooked and it made no difference. Pulled the plugs AGAIN! and it appears the truck is running really rich
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Old 12-02-2018, 09:54 AM
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Considering posting pictures of this POS to see if any of you are interested in taking it off of my hands.
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Old 12-02-2018, 12:52 PM
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Originally Posted by Cumminsguy1 View Post
funny you brought up using a jumper last night I had a similar idea (went to see if I can pull a code but nothing) anyway when I plugged the jumper in the idle did not change. I'll go check the hose now for possible cracks but it looks to be in good shape. I got a TPS ordered from 22re Proformance and should be here in 2 days, really hope that's the issue because I have checked EVERYTHING!
That would tell me the TPS is either way out of spec or it is faulty and that would certainly cause issues with lean or rich. That idle has to drop with the jumper in. If it doesn't I would strongly suspect the TPS..
read here - http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
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Old 12-02-2018, 12:57 PM
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Originally Posted by toyospearo View Post
That would tell me the TPS is either way out of spec or it is faulty and that would certainly cause issues with lean or rich. That idle has to drop with the jumper in. If it doesn't I would strongly suspect the TPS..
read here - http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
cool once I get the new TPS installed I'll get back to you guys. If it still dont work I guess possibley a new Coil would be next replacement but I really dont see that being the case
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Old 12-07-2018, 01:21 PM
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Well got the new TPS on and it made no difference!!
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Old 12-07-2018, 06:22 PM
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Well damn. If new mexico was a little closer I would come help out. Sounds like you have done about everything. You sure the compression tested good?
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Old 12-07-2018, 11:54 PM
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A tiny, obscure, overlooked piece is the fuel pressure regulator valve...
it's located at the back of the intake plenum, by the firewall... if the check valve inside the pressure regulator is not working properly it lets fuel bypass and sends it to the tank... instead of to the injectors...
not sure that would make it pop though...
I'd first try to figure out if it is a fuel problem or fire problem... and eliminate 1/2 of the possibilities.

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Old 12-08-2018, 04:09 AM
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It sounds to me like it's missing, and that's why you don't have any power, and that's causing the backfiring because of fuel that's not getting burned. Put a timing light on it, and see if it is in time.

When is the last time maintenance items were checked/changed like spark plugs, spark plug wires, distributor cap, and rotor?

Last edited by snippits; 12-08-2018 at 04:11 AM.
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Old 12-08-2018, 07:33 AM
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Originally Posted by snippits View Post
It sounds to me like it's missing, and that's why you don't have any power, and that's causing the backfiring because of fuel that's not getting burned. Put a timing light on it, and see if it is in time.

When is the last time maintenance items were checked/changed like spark plugs, spark plug wires, distributor cap, and rotor?
last time everything was changed was probably about a year ago, the person I bought it from "rebuilt" the motor (did a piss poor job) but everything for the most part is new. I think I'm going to give it a week or 2 before I start messing with this pos and hopefully find something that has been overlooked
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