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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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Discussion Starter #1
Hey everyone,

I am a new owner of a 1988 Bronco and I have a question. I am an old muscle car guy - I built a 1966 Mustang from the ground up back in the 90s, so I know my way around a simple engine compartment pretty well. However, when it comes to this booger, with tons of wires, vacuum lines, a throttle body instead of my old Holley double-pumper, and computer-controlled devices, I am a bit lost.

That said, my engine (a 302 with an AOD behind it) seems to want to bog down. It seems like it may be running rich, but since a simple turn of a screw doesn't adjust fuel mixture here, I'm not sure how to approach this. It seems to run pretty well at idle, and if I "feather" the throttle, but if I get down on the throttle at all (more than about 1/3 of the way to the floor), it bogs down. I back off, and it accelerates better, but still not well.

I have replaced the following since purchasing it two weeks ago: battery, spark plugs, wires, distributor cap and rotor, ignition coil, PCV valve (and grommet and hose), air filter and breather filter, and the O2 sensor. I have set the timing with a light to 10* BTDC. The fuel filter appears brand new underneath, so I haven't changed that yet. I haven't tested fuel pressure yet - I borrowed a tester, but it didn't have the correct adapter to screw onto the fuel rail. I have fixed a couple small vacuum leaks that I found, but there may be more.

Any advice or recommendations? The check engine light is not on, and it does work since I see it when I turn the key on. The fuel pump (I think) turns on for about 2 seconds when I turn the key on also. There is a small exhaust leak on the left manifold, but that shouldn't cause this issue I don't think.

I welcome anyone to weigh in here...I don't have any more bright ideas. Thanks!
 

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Premium Member
1989 Eddie Bauer 5.8, C6, True Trac diffs, 4.56 gears, 4" C&T lift, 130A 3G Alt, 35" Grabber AT2s
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557 Posts
Possible exhaust obstruction - clogged catalytic converters?
^^^^^ Agreed. Does it still have a cat? If so, try temporarily removing it (OR permanently :goodfinge) and see if it still bogs down. You also have to keep in mind that this is a 5K pound monster, not a 2500 pound pony car.
 

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Also, the fuel pumps on these trucks are known to have problems at this age. Yes, I said 'pumps' - your 88 actually has two. If it's acting anything like this, it's usually going to be one or both of your pumps.


That was flat to the floor with a malfunctioning in-tank pump but a new high pressure pump (which is mounted on the frame rail.) This is what it is actually supposed to do.


First thing for you to do is check the fuel pressure at the rail. Ford fitted a nice Schrader valve on the rail so you can check it with something as simple as a cheap tire pressure gauge (warning, it's messy and you're going to get gasoline sprayed). Yes, the other name for a Schrader valve is "the same one on your tires' valve stems."
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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3,403 Posts
Discussion Starter #5
Thanks - I actually did think of that (the catalytic converter) and I almost bought one as part of my "getting it running better" shopping cart buy. I'm glad I didn't, because when I crawled underneath to replace the O2 sensor, I noticed that there was no cat...at all. Other than a dead rat in the pipe somewhere (it was sitting a while - haha), I don't think an obstruction is the issue. The exhaust system from the Y-pipe back looks new. It seems like a fuel delivery problem, but other than replacing everything, I don't know exactly how to diagnose the issue.
 

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Thanks - I actually did think of that (the catalytic converter) and I almost bought one as part of my "getting it running better" shopping cart buy. I'm glad I didn't, because when I crawled underneath to replace the O2 sensor, I noticed that there was no cat...at all. Other than a dead rat in the pipe somewhere (it was sitting a while - haha), I don't think an obstruction is the issue. The exhaust system from the Y-pipe back looks new. It seems like a fuel delivery problem, but other than replacing everything, I don't know exactly how to diagnose the issue.
Check my post immediately above this one. You need to check your fuel pressure. I think you will find that one or both of your pumps are having problems. Sadly common in this day and age of ethanol laced gasoline.
 

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Yo Mike,
Welcome!

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
Some basics;
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First

Post Code(s) here according to:
KOEO
&
KOER
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See my vacuum leak test in post #11

See Booba's
Replace Plastic Vacuum Hoses with Rubber - Ford Bronco Forum
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Inspect air intake from inlet through throttle body.

If no maintenance record was presented by seller, figure that fuel filter should be replaced.
Then check pressure.
87-89; Fuel Injected Engines - Two electric pumps are used on fuel injected models; a low pressure boost pump mounted in the fuel tank and a high pressure pump mounted on the vehicle frame. The low pressure pump is used to provide pressurized fuel to the inlet of the high pressure pump and helps prevent noise and heating problems. The externally mounted high pressure pump is capable of supplying 15.9 gallons of fuel an hour. System pressure is controlled by the pressure regulator mounted in the engine.
Key on, engine off is 35 to 45 psi
Key on, engine running is 30 to 45 psi
Test pressure at the fuel rail with a gauge.

Connect FP Relay (terminal shown below to any ground to force the fuel pump(s) on when the key is in RUN.



Fuel Pressure Regulator (FPR) Test; "...Pull the red vacuum line & check for gasoline...There shouldn't even be the ODOR of gas in it."

Note: Maximum fuel pressure is obtainable at WOT or the vacuum hose removed from the fuel pressure regulator.

If fuel lines/systems have been drained or evacuated, it may take up to 15 seconds to obtain the pressure specified.

Run the fuel pump for 30 seconds minimum.
note fuel pressure on the gauge.
Verify whether the fuel pressure remains within the specified 5 psi for 1 minute after engine is turned off.
BY FORD
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Check spark plug routing:
Diagrams for 5.0, 87-93 & 94-96 5.0 HO - INCLUDES 5.8; MIESK5 NOTE; The firing order for 1987-1993 5.0Ls is 1-5-4-2-6-3-7-8. If #7 and #8, or #2 and #4 spark plug wires are routed next to each other at the separation bracket, an induction crossfire condition can occur. & The firing order for 1994 5.0Ls & all 5.8Ls is 1-3-7-2-6-5-4-8. On these vehicles the #1 and #3, or #5 and #6 spark plug wires must be separated to eliminate the possibility of an induction crossfire. To eliminate the possibility of the coil wire becoming disconnected, route the coil wire under the spark plug wires at the distributor cap. MIESK5 NOTE; Misfiring spark plugs may cause an unburned fuel air mixture to pass through the catalyst, which could cause higher than normal catalyst temperatures. Refer to the following procedure for service details. Check secondary ignition, hook the vehicle up to an engine analyzer and check for a secondary ignition misfire.
See diagrams by Tank92
***

Posting this next article for posterity because I see that you know this procedure.
How to properly set the timing on a 302 or 351
By sackman9975
 

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These EFI systems in these trucks look more intimidating than they actually are. In fact, at one point these EEC-IV systems were used to teach the basics of fuel injection to high school kids in some states.

Just get yourself a decent autoranging multimeter and you'll find it's rather easy to diagnose issues for the most part. You need one anyway, if you're going to diagnose any other electrical issues on a truck like these.
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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3,403 Posts
Discussion Starter #12
Good info - thanks sackman9975! I have not checked for spark plug wire crossfire either, and the coil wire under plug wires tip is a good one. I'll repost when I get this done - probably later this week.

Thanks for the tips everyone!
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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3,403 Posts
Discussion Starter #13
I did get a nice little shock the other day when turning the distributor to set the timing, haha. It looks like, by the harness of wiring attached to the distributor, the high rev advancing of timing is done electrically? I don't see centrifugal weights for mechanical nor do I see a vacuum regulator for vacuum advance.
 

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Correct, advance and retard is electric (actually, *electronic*) and occurs not just at higher RPM but at all times. EEC-IV includes a knock sensor in most iterations and the system can pull timing if it hears the engine knocking to avoid engine damage. It can also advance the timing to just before the engine starts knocking for better fuel economy and performance. EEC-IV isn't just a basic fuel injection system, it's actually a full engine management system where it also controls the ignition.
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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3,403 Posts
Discussion Starter #17
I am beginning to think that there may be more going on here than just bad timing or fuel starvation. I checked the fuel pressure and all looks good at around 40 psi. I am starting to think more about the valves and/or loss of a cylinder. The number 8 cylinder is suspect in that the plug doesn't show the look of one that is experiencing combustion, I have an exhaust leak on that side (likely number 8), and I am getting a bit of spitting backfire as I drive. Acceleration is sluggish, and WOT doesn't do much when driving.

I'm thinking maybe a bent push rod, rocker stud broken, rocker came off of valve, something along those lines. Hopefully, I don't need a new cam or have to remove the head(s).

Thoughts?
 

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The #8 plug looking fouled my be because the PCV vacuum line reroute has not been done. Look to see if the PCV (located toward the back of the passenger side valve cover) vacuum line is routed to the back of the upper intake manifold. If it is, then you should investigate rerouting it.
One method is to take the vacuum line to the brake booster and route it to the back of the intake, and take the PCV line and route it to the center of the upper intake.
Having the PCV vapors directly above the #8 cylinder seems to excessively load up that cylinder with combustion byproducts and can lead to #8 valve and ring issues.
Search for PCV Reroute.

(If #8 is already carboned up, or the valve(s) are leaking, the rerouting of the PCV line may be too late to for your engine.)
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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3,403 Posts
Discussion Starter #19
Hmm, ok. Well, I just finished taking another look at this situation. The plugs that are in there now are new - maybe 50 miles or so, and I pulled number 8 and it looks pretty good, but there was a little oil on the plug threads. I cranked the engine and pulled the number 8 wire from the distributor, and it drastically lowered and roughened the idle, so I guess the cylinder isn't dead.

I will be getting some hose to do the PCV/brake booster vacuum line relocation today, but I have a feeling there may be a vacuum leak somewhere. I have found several tiny vacuum lines that were broken or not attached, but there may be something bigger leaking. I noticed one "cut" hose on the back of the right bank that I assume went to the CAT? I would hope that whoever removed the CAT would have plugged that hose, but maybe not?

Maybe I'll try the cigarette smoke into the intake test to pinpoint any more leaks? I'm still wondering if the timing chain is stretched or jumped a cog, or if an exhaust valve isn't opening due to a broken rocker stud or something else like that.

It seems to idle OK, a little rough, but there is just no power. I test drove it yesterday and was able to get it up to about 60 mph, but that was like 0-60 in about 45 - 60 seconds, and on level ground. Up a hill it struggles. Oh, and there is a significant vibration on acceleration too - from about 5 - 35 mph range.

Zeroing in on this issue is getting difficult.

Any more thoughts on anything I am overlooking? Thanks!
 

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Yo,
Did you see my vacuum leak testing post #11 @ http://www.fullsizebronco.com/forum/21-noobie-bronco-tech-questions-flame-free-zone/206824-help-dtc-codes-idle.html
Includes hvac system.


Air Inlet Tube Location pics at Catalytic Converter in an 89 5.0; w/High Temperature Silicone Hose by rcracerx

Air Injection (AIR), Secondary Air Injection Overview "...And for the fuel that wasn't burned in the combustion chamber, we need extra airflow pumped into the exhaust system. This air with the heat of the exhaust creates further break down of HC, CO, and Nox into CO2, H2O, and N2. The catalytic converter can accept all of the airflow without fear of over heating during cruise. We need hot exhaust gasses to help complete combustion and converter operation. Air is pumped into the converter, but will dump to the atmosphere after several minutes to prevent overheating the converter. The converter is cooled by air passing under the vehicle..." READ MORE
by Ryan M
 
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