86 Bronco 302 EFI

Previous owner installed wrong alternator without regulator that fried multiple sensors. Finally got it running acceptably. After sitting for some time, tried to start it but it would barely run and had no power. When I unhook the vacuum line to the MAP sensor, it runs MUCH better. Still very little power, but runs. Is this definitive proof that the MAP sensor is bad?

 

Pull the codes and see if you get a MAP sensor code from it.

 

Will a MAP sensor code cause the Check Engine light to come on? There's not one on right now. I don't have a code reader. Is there another way to pull them?

 

I think you can use a test light and a jumper wire?
I have not looked into it deeply as I dont have a computer on my 81 F100 so no need to look but have seen posts on it.
Look at the top in the FAQ or Tech areas to see there is a sticky on pulling codes.
Dave ----

 

You have one of the very first generation fuel injected trucks. I bet you do not even have a check engine light, the first ones didn't.

If you plan on keeping this thing, you will have to bone up on the efi system and how to pull the codes. Here's how to do it.

https://www.fordtruckzone.com/thread...canner.659319/

 

Your '86 Bronco 5.0 EFI has a light. It probably says EMISSIONS and illuminates with key on engine not running. No bad sensor or code will turn it on. It only lights while running when it has been triggered by the "inferred mileage sensor". That sensor uses an algorithm to decide when you need to take your truck to the dealership for an emissions checkup. There is no input from the ECM or anything else. Only the IMS. Therefore, you must do the code extraction exercise already mentioned. It's not hard. Heck, it's fun.

If some alternator mix up, voltage spikey, smoke the sensors event happened, you need to understand that the Engine Control Module, ECM took the same hit first. The ECM is a firewall between the charging/electrical system and the Emissions/Fuel Management system. All sensors, MAP included, get their power from the ECM.

There is a test for the MAP sensor. You need a multi- tester with a hertz setting. Not a $10 Amazon special. Pros just keep a known good sensor in their toolbox.

FWIW: The MAP has three wires. One (orange) has 5v reference (power). The blue? wire carries 2.5v and is the wire you check for a variable frequency (hertz) at different vacuum pressures. The third wire (black) is a ground back to the ECM.

 

I tried using my test light and it would not light up. Tried using the continuity setting on my multimeter and was able to detect some flashing, but it was too confusing to figure out what the codes were. I guess I'll have to break down and buy a code reader.

 

Bought a code reader and only got two codes. 87 and 18. I'm pretty sure the 87 is because the fuel pump relay and socket has been replaced and they failed to wire it through the computer, which explains why the fuel pumps run constantly while KOEO. The 18 is what bothers me. The book says, "Loss of tachometer input/IDM circuit failure/SPOUT circuit grounded." The tach works properly and I checked the SPOUT circuit and it is not grounded. So that leaves the IDM, which I know nothing about. Any input?

 

You are probably right about the 87 if it has been re-wired.

Code 18 means there is a loss of tach signal to the ECM, not the tach in the dash. Two totally separate worlds there. Your ECM and the fuel injection system itself is not really tied into the rest of the truck much at all. You have powers and grounds to the EFI system, and the check engine light in the dash, there is not much else, everything else is just like any other truck that year whether it had EFI or not.

The Spout wire is important, it's what controls the timing inside the distributor. If you look at the distributor, it will have a rectangle looking module mounted to the side of it with a bunch of wires coming out. Follow these wires out, one of them will stray from the others for a brief distance and there will be a shorting plug or some other connector in the wire. See if yours is missing. The jumper or shorting plug is what you take out to time the engine with a timing light. It takes timing control away from the computer so you can twist the distributor around and set it according to the sticker at 10 BTDC with a timing light shining on the front pulley. Once you get it set, you plug the spout jumper back in and that gives timing control back to the computer.

See if you have this jumper or connector in place. It should be close to the distributor wires somewhere.

 

Jumper is there and has continuity across the legs and neither side of the SPOUT connector is grounded according to my multimeter.

 

You can double check this wire for integrity at the large ECA connector. If it checks good continuity all the way to the spout connector, then it's either going to be the TFI module on the distributor is faulty, or the ECM is faulty. It's supposed to be pin 36 on the ECA side. I believe it's a yellow/green wire.

 

I've already replaced the ECM assuming the former faulty alternator could have damaged it. I replaced the TFI because I had a weak spark. I've read something about the PIP in the distributor. Is there a separate code for that?

 

PIP is code 14. This whole Spout deal is about controlling the timing of the engine. Does the engine slow down when you unplug the spout? If not, take a timing light and hook it up properly, and with the spout plugged in, rev the engine and see what the timing does. If the spout is working the timing should be advanced some at idle (the engine should slow down when you unplug the spout and revert back to 10 BTDC) and you should see the timing mark advance on up when you rev the engine. If the mark just stays dead at 10 BTDC, the the whole timing thing is not working at all for some reason. The ECM thinks there is something wrong with the spout circuit.

 

Nothing changes when the SPOUT is unplugged. It does act like the timing doesn't advance properly when trying to rev the engine. What I don't understand is why when I unhook the vacuum line to the MAP sensor, it will idle without stalling and take throttle like it should. I will check continuity from the SPOUT to pin 4 on the ecm plug tomorrow. Thanks for all of the help! This Bronco is my son's first ride. He turns 16 in August and we've got to get it right!

 

A little under power is not a bad thing for a new driver.
Dave ----