91 cruiser map sensor issue?

[JP80]

Hello, I'm having issues with this beast and I'm at a loss. First of all please forgive me for my ignorance. I'm a simi new owner and can do basic part replacements. Troubleshooting is a whole differant area for me and left for a shop mechanic.

This beast is a straight 6, and im having issues with the truck underload. To me it feels like the truck is surging around 2k rpm. I've replaced all spark components except for distributor and coil pack. The truck needed a tune up was getting around 8-9 mpg now it's getting around 10.5. I broke my map sensor trying to take wiring harness off to clean the intake manifold. ( removed screws instead of spring clip and broke solder on the board) so I found one in Tennesee of the same year model. Had it shipped to me here in Texas. Replaced and fixed my self made problem. Then a whole new list of issues started. ( another story)

I did install the wrong plugs from what my mechanic has told me. I put in platnums when oem calls for v guard. Apparently the coil pack wont support the voltage needed for the platnums.

He also said it may be a clogged injector but wont know until he gets all plugs pulled. (Only got about an hr into it right now) Said it is running lean. Bonus is that he has worked on this machine for several yrs since he is a family friend and my dad owned it before me.

So my questions...

1. Is there an aftermarket workaround for the map sensor?

2. Any "test" that have been figured out or known? Other than unplugging the wiring harness and truck dies.

Any info would be appreciated and if you need more specs I'll find out for ya.

Thanks in advance.

 

[BILT4ME]

Search out all posts from @jonheld as he is the best authority on the 91-92 3FE truck. He has a complete troubleshooting guide for that truck.

You MAY be able to locate another AFM for you truck from a 62 series, but I am not positive.

You can also source parts here:

Shop OEM Toyota Parts Online | Ourisman Toyota Parts

Find Genuine OEM Toyota Parts and Accessories When You Shop Online. This Toyota Parts Catalog Includes Discounted Quality Parts You Can Trust To Perfectly Fit Your Vehicle!

toyotaparts.mcgeorgetoyota.com

 

[Mixelplix]

93 camry AFM works on the 3fe. I'm running one. But I suspect your replacement is working just fine.

I've never heard of anyone having issues with platinum plugs.

When you say surging at 2k, do you mean it feels as if it immediately gains power at 2k? In my experience that's vacuum line related. There's quite a few vacuum lines, and hard lines associated with the 3fe engine.

Do you have an illuminated check engine light? If so, have you checked the codes?

Your surging and poor gas mileage lead me to believe you need a solid baselining. I know you said you're a novice mechanic, but I would perform the following (assuming you have no check engine lights):

Get a copy of the factory service manual
Follow the instructions for adjusting your valves
Follow the instructions for checking your timing
Replace all your vacuum lines one at a time. I believe they're 4 and 6 millimeter.
Check hard vacuum lines at the rear of the valve cover

If you have a check engine light:
Get a copy of the factory service manual
Follow the instructions for checking the codes
Cross reference the code to the table in the FSM, and follow the troubleshooting information in the relevant section

Best of luck! I've learned that it's best to start with the basics with the 80 series platform, and especially with the 3fe's. They're very simply built, so the issue is usually 'oh look, this hose is disconnected'.

 

[JP80]

Search out all posts from @jonheld as he is the best authority on the 91-92 3FE truck. He has a complete troubleshooting guide for that truck.

You MAY be able to locate another AFM for you truck from a 62 series, but I am not positive.

You can also source parts here:

Shop OEM Toyota Parts Online | Ourisman Toyota Parts

Find Genuine OEM Toyota Parts and Accessories When You Shop Online. This Toyota Parts Catalog Includes Discounted Quality Parts You Can Trust To Perfectly Fit Your Vehicle!

toyotaparts.mcgeorgetoyota.com

Thank I'll forward this link to my mechanic

 

[JP80]

93 camry AFM works on the 3fe. I'm running one. But I suspect your replacement is working just fine.

I've never heard of anyone having issues with platinum plugs.

When you say surging at 2k, do you mean it feels as if it immediately gains power at 2k? In my experience that's vacuum line related. There's quite a few vacuum lines, and hard lines associated with the 3fe engine.

Do you have an illuminated check engine light? If so, have you checked the codes?

Your surging and poor gas mileage lead me to believe you need a solid baselining. I know you said you're a novice mechanic, but I would perform the following (assuming you have no check engine lights):

Get a copy of the factory service manual
Follow the instructions for adjusting your valves
Follow the instructions for checking your timing
Replace all your vacuum lines one at a time. I believe they're 4 and 6 millimeter.
Check hard vacuum lines at the rear of the valve cover

If you have a check engine light:
Get a copy of the factory service manual
Follow the instructions for checking the codes
Cross reference the code to the table in the FSM, and follow the troubleshooting information in the relevant section

Best of luck! I've learned that it's best to start with the basics with the 80 series platform, and especially with the 3fe's. They're very simply built, so the issue is usually 'oh look, this hose is disconnected'.

What I mean by surge us while on highway and rpm is around 2k we can feel a surge in the motor or a pulse.. idk how to explain. It's not violent like if the plug wires are in the incorrect position. It's more like it's not firing all the time. Seems to idle fine when I park and also in gear underload. Most noticable when driving.

No codes/lights or I would have had those read already.

No vacume leaks as we can see. Everyone I have taken it to has sprayed brake cleaner around all the lines and motor didnt rev up.. (I've been replacing hoses just incase) but nothin yet.

Thank you for your reply

 

[Marco Lau]

EGR and vacuum lines associated with them. I removed my EGR, and smog related solenoids and the surge was gone and idles smooth FWIW....

 

[JP80]

EGR and vacuum lines associated with them. I removed my EGR, and smog related solenoids and the surge was gone and idles smooth FWIW....

Man I'm throwing hailmarys rn

 

[jonheld]

Man I'm throwing hailmarys rn

The 3FE is basically a fuel injected tractor motor from 1986. There is no magic electronics on this one. The factory service manual should be your bible.

Your truck is now 28 years old, so some of the components are in need of replacement. The majority of parts are still available from Toyota, and I STRONGLY suggest that you keep it as close to OEM as possible. This engine DOES NOT LIKE aftermarket ignition components. Cap, rotor, plugs, wires, coil, igniter, really want to be OEM parts.

Fuel delivery: there is a mesh pre-filter on the fuel pump that will clog over time and should be replaced every 100K miles. There are numerous writeups here on Mud. Sometimes called a "fuel sock" for some reason. This pre-filter will collapse on itself once the fuel in the tank gets warm and block the pump intake. Usually happens under high loads after extended driving, like on a highway trip.
There is also an inline fuel filter below the distributor on the inside frame rail. While this is usually not the problem, yours is now 28 years old and owes you nothing.

Vacuum system and unmetered air: The top half of this motor wants to be air tight. Although most unmetered air leaks will cause a rough idle, it should be noted that any air leaks will distort the reading that the ECU uses to adjust fuel delivery.
ANY vacuum leak or clog will cause issues, especially related to the EGR valve and EGR modulator (the 2 flying saucers on the top left of the intake). These both have diaphragms that break down over the years.
Vacuum hoses become brittle over time and don't seal well anymore.

Engine coolant sensors: there are a variety of sensors on and around the thermostat housing. While they usually remain functional for the life of the vehicle, the connectors become horribly brittle with age and tend to crack. Extreme care should be taken when screwing around with them, or just replace them. Below is a picture with part numbers. The water temp sensor for the ECU is a critical one.

Remember, 1986 technology. This ECU is 1st generation fuel injection. All sensors have a very narrow operating window that the ECU can "see". The mechanicals have to be correct first.

http://www.sdsysdesign.com/tlc/images/Strife/3FE%20TuneUp.pdf

This is a basic parts list for base lining your truck.

Below is a picture of the thermostat housing.

 

[JP80]

The 3FE is basically a fuel injected tractor motor from 1986. There is no magic electronics on this one. The factory service manual should be your bible.

Your truck is now 28 years old, so some of the components are in need of replacement. The majority of parts are still available from Toyota, and I STRONGLY suggest that you keep it as close to OEM as possible. This engine DOES NOT LIKE aftermarket ignition components. Cap, rotor, plugs, wires, coil, igniter, really want to be OEM parts.

Fuel delivery: there is a mesh pre-filter on the fuel pump that will clog over time and should be replaced every 100K miles. There are numerous writeups here on Mud. Sometimes called a "fuel sock" for some reason. This pre-filter will collapse on itself once the fuel in the tank gets warm and block the pump intake. Usually happens under high loads after extended driving, like on a highway trip.
There is also an inline fuel filter below the distributor on the inside frame rail. While this is usually not the problem, yours is now 28 years old and owes you nothing.

Vacuum system and unmetered air: The top half of this motor wants to be air tight. Although most unmetered air leaks will cause a rough idle, it should be noted that any air leaks will distort the reading that the ECU uses to adjust fuel delivery.
ANY vacuum leak or clog will cause issues, especially related to the EGR valve and EGR modulator (the 2 flying saucers on the top left of the intake). These both have diaphragms that break down over the years.
Vacuum hoses become brittle over time and don't seal well anymore.

Engine coolant sensors: there are a variety of sensors on and around the thermostat housing. While they usually remain functional for the life of the vehicle, the connectors become horribly brittle with age and tend to crack. Extreme care should be taken when screwing around with them, or just replace them. Below is a picture with part numbers. The water temp sensor for the ECU is a critical one.

Remember, 1986 technology. This ECU is 1st generation fuel injection. All sensors have a very narrow operating window that the ECU can "see". The mechanicals have to be correct first.

http://www.sdsysdesign.com/tlc/images/Strife/3FE%20TuneUp.pdf

This is a basic parts list for base lining your truck.

Below is a picture of the thermostat housing.

View attachment 2015863

Thank you for this info,this will be vital for my continuing dive into this truck. Btw I've already replaced the fuel filter under the distributor on the frame, I do understand that the age of the vehicle is a factor and as I work on something I replace all I can with new. Grated I've yet to find a new AFM in the box, but I do belive that this one I have isnt the problem.

 

[JP80]

Update: mechanic replaced plugs with V-power which he told me are OEM replacements. Granted this was done before JonHeld passed on the info. I've yet to find out why 2 of the plugs were bad as I've been busy with work, and my dad picked up the truck.

But he returned 4 of the old ones and gave me 2 extra. He did say that 2 of the plugs he pulled were lean. He also said that I didnt have the plug wires all the way in the plug wire boot.... so maybe my mechanical skills just got knocked down a bit..

As I did take it for a test drive it did run 100% better. Same as it seems to when I replaced the plugs the 1st time. I drove it about 10 mile to let the motor fully warm up. As I pulled up to a stop sign I noticed the rpm flutter and drop close to 200 rmp, just for a second then back up to around 800 rpm. So when I pulled up to my house I left it in gear and the rpms drop intermittently. So I am starting to believe that spark isnt the issue.

I do wonder... would the fact that the cruise control not working be part of the issue? Since the throttle cables work through this part. I'm leaning towards no, but I'm really unsure.

Thanks again all, I really do appreciate all the info. I will start by checking for clogs/obstructions in the vacume lines and possibly replacing the "flying saucers"

 

[jonheld]

I repeat myself. 1986 technology. Look for the simple things first.
If your idle is dropping or getting rough only when she's warm, then you have unmetered air entering the system. If it was an electrical issue, most likely it would be constant.
Suspects are: torn or loose intake plenum, dried up or cracked PCV valve gasket, dried up or loose valve cover grommets, loose oil fill cap, etc.
Again, the top end of the motor wants to be air tight. That's why there's a gasket on your oil fill dipstick, on your oil fill cap, etc. Any air getting into the system will cause rough/low idle.
Make sure that the intake plenum (big black rubber tube coming off the air cleaner) is not torn at the bellows or has loose clamps. Any leaking air downstream of the AFM will corrupt the air flow reading that the ECU uses to adjust fuel delivery.

Mechanicals: when was the last time the valves were adjusted? The FSM calls for every 15K miles. If yours haven't been done in 20 years, you might be overdue. This won't effect hot idle issues, but the valve cover gasket and grommets will need to be replaced. If they're 28 years old, they're way overdue.