1987 Full Size Ford Bronco 302 Engine Surge/ Failed Emissions. Arizona NOX standard 5.50: Ours 9.65. HC: good CO: good Hi, My husbands Bronco is surging on idle and we just replaced the EGR valve, EGR Sensor, air filter, refueled with Premium Unleaded. It is still surging badly cold but not as bad warm. Fuel filter was replaced about three months ago and fuel pump was replaced about eight years ago. The engine was replaced also at that time. He passed emissions well below levels in 2009. What can you guide us to for engine surge?

DEPENDING ON WHAT PORTION FAILED IT COULD BE MANY THINGS. HC, NOX, CO? IT COULD BE TOO RICH, TOO LEAN, TOO HOT, TO COOL.WHAT FAILED?

Sounds like you lost O2 Control

Check fuel trim & data with professional
scanner & such

You done as far as working at home, you did all
you can

You have a rich condition (CO)

Seems as though the coolant sensor is not working &
your in open loop

There are three kinds of 302s made from 1982-2001. 5.0L HO This engine was used in 1983-1995 Mustangs, Mark VII Lincolns, and some T-birds and Cougars. All Explorer 5.0L engines are 5.0L HO engines as well. They use the 351W firing order, 1-3-7-2-6-5-4-8. Except for the 1983-84 Mustangs, all of these engines are roller cam equipped. They use a reverse rotation water pump and front cover. The 1994-5 Mustang and all Explorers use a unique front cover and water pump. 5.0L Full Size Car This engine was used in 1982-1990 Crown Victoria and Grand Marquis. They use the 289-302 firing order, 1-5-4-2-6-3-7-8. Most of these cars are not roller cam equipped, however sometime in the early 1990s they started using roller cams but retained the 302 firing order. They use a standard (clockwise) rotation water pump and front cover. 5.0L Truck (except Explorer) These engines are similar to the Full Size Car engines, except they use different intake manifolds and camshaft profiles. They also use the 289-302 firing order, 1-5-4-2-6-3-7-8. They also began using roller cams sometime in the early 1990s. They use a reverse rotation water pump and front cover.

Good Luck

Sticking egr will raise everything except nox. Bad o2 bad cat hard to give an accurate diagnosis with out checking it

there is a two piece control module and pick up in distributor you could replace these or try a used distributor

fuel pump

Look behind the motor, next to the firewall. There's a vacuum check valve that keeps the air gulp pump from pressurizing the crankcase. Mine was shot; had the same symtoms. Also, make sure that the EGR valve is closing at low idle.

You don't need an engine light to check the codes. First, do a KOEO (key on, engine off), but, let me tell you, when this happened to me (1986 Full size with 302 EFI, multiport injection) NOTHING showed up. No one, not Ford, not emission specialists, nada, knew the vacuum check valve existed.

By the way; are you getting motor oil in the air filter housing?

Hi Don,

First, thank you for asking me for my input on this. It just so happens, that I used to own a Ford ranger that had the same engine as yours. It was a 1990, but there are few changes to these model years.

Anyway, there is only one reason that your HC levels would be high. Your engine has WAY too much unburned fuel in the exhaust. The same reason applies to high CO levels. Too much fuel and/or not enough air.

Below is a link that you may find very helpful. It explains exactly what we are talking about here and also lists some of the possible causes.

EMISSIONS ANALYSIS

Incidently, when I had the same emissions failure on my truck, replacing the air filter and replacing a failed MAP sensor fixed it. - I did NOT have to replace the catalytic converter. If the numbers are as high as you listed above, you will only destroy a new converter anyway because there is obviously not enough oxygen in your exhaust system for the catalyst to function properly. Those numbers are nearly DOUBLE the allowable maximum. If the engine is running correctly and the catalyst is good, your numbers will be WAY BELOW those maximum numbers.

Please understand that I am NOT telling you to replace your MAP sensor without proper diagnosis. There are many possible causes here. Please click the link above and read the article. It will help you to understand what is going on here.

Change the lambda/oxygen sensor in the exhaust.

Check vvt servo motor