88 Oil Pressure Issues? Help!

[Art5]

I just bought a 1988 Bronco XLT 4x4 with the 302 and the AOD trans. I drove it around town for a day and it ran really well, but when I drove it 15 miles to where I work I ran into problems. First, I noticed that at a steady speed of 50mph intermittently I was getting a check engine light, and it felt like she wasn't all there at the pedal when that light came on. I pulled over at a gas station, put gas in it and checked my fluids, and I was about a half a quart low on oil. There was nothing on the ground under the truck, so I bought a quart of oil and left for work. Then when I came to a stop at a red light with the truck in gear the oil pressure gauge dropped and I got red light that said 'ENGINE'. When I gave it gas again and took off, the oil pressure gauge came back up, and the light went away. But every time I came to a stop the same thing happened. When I went on break I took my supervisor on a test drive b/c he used to have a bronco and is pretty good with cars. We drove it down the street and the first time I came to a stop the oil pressure gauge dropped to nothing, the red engine light came on, and the truck stalled and would not start again. There were no fluids on the ground under the truck. We dragged it back to our lot with a chain, and I was able to get it started so I backed it into a spot and parked it. I have no clue what's wrong with it so I thought I would ask the forums. Any and all help would be greatly appreciated as I now have $10,000 invested in my two trucks and neither of them drive down the road. So this is my nightmare, give me your input.
    Thanks guys,
                        Art
 

 

[miesk5]

yo ART,

WELCOME!

Did you hear any metal on Metal Sounds before engine stopped and Red Lamp lit?

Circuit Operation 87-96 F Series & Bronco; "...In recent years, Ford Motor Company has been doing something I view as a bit sneaky. They have taken the oil pressure gauge and turned it into a glorified warning light. It says it's an oil pressure gauge, it looks like an oil pressure gauge, but in reality it is not. starting in 1986 a change was made on some models that altered the function of the oil pressure gauge as we knew it. The variable resistance sending unit was replaced with an open/closed switch and an in-line 20 ohm resistor was installed between the gauge and the switch. Anytime you have more than 4.5 psi of oil pressure, the switch closes, completing the circuit from the gauge (with the 20 ohm resistor in-line) to ground. This then results in a gauge that reads just above the middle. As you can see, there is no variation to the gauge needle in this circuit. It will either read no oil pressure or half-scale (normal oil pressure). On this style of gauge circuit, if the oil pressure gauge reads in the middle, it is telling you only one thing - you have more than 4.5 psi of oil pressure. How much more is anyone's guess at that point. When oil pressure drops below 4.5 psi, the gauge will return to 0 and alert the driver of a problem...Ford released a TSB (#88-5-14) for 1987-1988 F Series and Broncos that called for converting the variable resistive style oil pressure gauge circuit to the switch style circuit - if the customer complained of low or erratic oil pressure readings. The kit contains an oil pressure switch and an in-line 20 ohm resistor that is to be connected between the end of the existing sending unit signal wire and the new switch. The variable resistance oil pressure unit removed from the vehicle is then discarded. I want to point out some diagnostic problems that can arise from this circuit. First, if you are working on this switch style oil pressure circuit (with the in-line 20 ohm resistor) and install a variable resistive sending unit in place of the oil pressure switch, the result will be a gauge that reads lower than normal due to having two resistors in series, the fixed 20 ohm in-line resistor and the variable resistive sending unit. On the other hand, installing the open/closed switch on a vehicle that incorporates the conventional oil pressure gauge circuit will result in a pegged gauge needle after starting the engine. Sometimes you can tell that you need a switch instead of the variable resistive sending unit by the presence of the in-line resistor a few inches from the switch connector. This is not a good rule of thumb though, since many vehicles have the fixed resistor on the back of the cluster, and some of the digital dashes have that circuit built into the cluster. To determine what style circuit you have, simply ground the sending unit wire with the key on. If the gauge reads exactly half-scale, you can be fairly sure you need a switch-style sender. If you ground the sender wire and the gauge pegs, a variable resistor-style sender is needed..."
Source: by James M at asashop.org

Test & Installation Tips in a 90; "...My oil pressure gauge was reading on the "N" of the NORMAL range. After doing some research it seemed like it could be the oil pressure switch, also known as a sensor or sending unit. Disconnect the wire from the switch, ground it to the truck and turn the key on. If your gauge quickly moves to the left, the problem is most likely the switch. The switch on my 5.8 is located near the oil filter. It is in a difficult spot to work on so I advise that you go to NAPA and get an Oil Pressure Switch socket to do the job. The cost is about $7-$8, this will save you time and will help you reinstall the new switch. Wrap some teflon tape around the threads and install. Make sure that it is in tight, I don't know about torque specs, I just put mine in quite snug. Hook the wire back on and start your engine. For me it was the cure. My oil pressure now reads over near the "M" on NORMAL..." miesk5 Note; The stock gauge & Sender will drop off after pressure reaches a certain level. You might actually have 5 psi, but the gauge will read 0 PSI & "...Technically all you need is 10 psi of oil pressure per 1,000 rpms . I still would not feel comfortable with less then 20 psi at idle. If it is lower then that, you can also get a thicker oil." by 420nitro
Source: by Canoeboy146

Suggest Install of the mech oil press gauge and test pressure prior to starting eng again

Also

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
http://broncozone.com/topic/14269-code-reader/?&pid=74587&mode=threaded

 
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test
 
turn off all accessories/lights, etc.

Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.

Do Key On Engine Off (KOEO) portion

 

[Art5]

Ok guys, time for an update. So the bronco sat in the parking lot for 3 days while I tried to get it running. I was losing a lot of oil (a quart and a half in 20 miles). But I couldn't find any oil on the ground. That's not why it wouldn't start though. We thought it was a fuel issue so I put a new fuel pump in it in the parking lot. It started, but I put it in gear. tried to drive it, and she stalled after 10 yards. I hated to do it, but I called a flatbed and had her brought here. After we installed a new cap and rotor we were able to get it running yesterday before we started work. It ran for 10 minutes straight while we had the computer on it. We have been working on it nonstop from dawn to dusk for two days. So here's what I've found out. Blown out valve cover gaskets on both sides, leaking onto the manifolds so it was evaporating before it could run to the ground. So we replaced the gaskets. Also, we replaced the cap, rotor, plugs, wires, coil, pcv valve, fuel filter, fuel pump, oil sending unit, and fuel pump relay. This morning after we finished hooking everything back up, I started it and it ran for a couple minutes, and then shut off. We were not getting power to the fuel pump. The brown wire at the relay has no power. We kind of bypassed it with a piece of wire to get power to the fuel pump. Now we have 40 psi of fuel pressure at the rail with the key on, but the truck still won't start. If we spray carb cleaner in there it will start, and if we keep spraying it it will run but as soon as we stop she dies. We thought for sure that replacing the relays would fix it, but to no avail. My truck still won't start, and I'm out of ideas. Please help.

 

[Seabronc]

Check the inertia safety switch.  They have a tendency to go bad after years of non-operation.  It is only there to shut off the fuel pump in the case of an accident.

Good luck,

>-

 

[Art5]

Updating again as I have just now stopped working on her for today. We tested the injectors and they are NOT pulsing.  Replaced distributor module/ignition module on the side of the distributor. No dice. I've ripped the computer out. It's sitting on the kitchen table, it looks like it has water damage; there is corrosion all over one side of it. I've ordered another one it should be here tomorrow. I've got my fingers crossed because after this I am completely out of ideas for this darn thing. Still want to hear what you guys think, please reply. 
                                   Thanks,
                                              Art.

 

[Rons beast]

Hey Art,

You got some great advice from M5 and Seabronc there but you didn't say if you spent any time following their suggestions.

Loosing a quart and a half in 20 miles on the manifolds would result in your Bronc smoking like a fog machine at an Ozzy Osborne concert.  There must be another problem. How many miles are on the truck?  When the oil preaure drops do you hear a rattle, or knocking noise?  What did the plugs look like when you changed them? Oil fouled?  When the truck won't start , have you confirmed that you have no fuel?  Confirmed you have spark?

getting us factual info as to what is happening will help work to a logical solution.  Throwing parts at the problem is expensive and can be frustrating, as you already know.

 

[Art5]

yo ART,

WELCOME!

Did you hear any metal on Metal Sounds before engine stopped and Red Lamp lit?

No, no metal on metal sounds or anything like that, although the truck did seem to vibrate, but that was probably just from the motor lugging

 

[Art5]

Check the inertia safety switch.  They have a tendency to go bad after years of non-operation.  It is only there to shut off the fuel pump in the case of an accident.

After bypassing the relay, there was power at the positive connector on the inline fuel pump, indicating to me that the inertia switch is not the problem

 

[Art5]

Hey Art,

You got some great advice from M5 and Seabronc there but you didn't say if you spent any time following their suggestions.

Loosing a quart and a half in 20 miles on the manifolds would result in your Bronc smoking like a fog machine at an Ozzy Osborne concert.  There must be another problem. How many miles are on the truck?  When the oil preaure drops do you hear a rattle, or knocking noise?  What did the plugs look like when you changed them? Oil fouled?  When the truck won't start , have you confirmed that you have no fuel?  Confirmed you have spark?

getting us factual info as to what is happening will help work to a logical solution.  Throwing parts at the problem is expensive and can be frustrating, as you already know.

The odometer reads like 85XXX it is the five digit I am sure it has rolled over.

No rattle or noises accompany the pressure drop, although I do notice a vibration.

I have confirmed that I have fuel at the rail, 40psi with the key on, engine off. I have also confirmed that I have spark. Lastly, I have confirmed that I have no pulse at the injectors.

 

[Rons beast]

Hey Art,

since you said earlier that you could get the truck to run, but then it would stall out, I would think that the fuseable links to the fuel pump relay and EEC are ok. To verify, check that you have power to the red (hot) wires on the injectors, (while cranking)

Power there = fuseable link and circuits all ok.

The injectors are switched on by the EECM providing the circuit ground. If you don't get a ground pulse while cranking the most likely problem is your EECM (comp)

Good Luck

 

[Art5]

So I put the new computer in yesterday, hit the key, and she fired up! She ran like a champ for a few minutes, no misses, no struggling, nothing like that. And then she just quit. Didn't sputter or idle funny or anything was running fine one second, and the next she just died. And wouldn't start again.:***

 

[Rons beast]

DANG!!!!

When it wouldn't start do you know if you lost fuel preasure, spark, or injector signal?

Any codes?...Did the CEL come on prior to the engine dying?

 

[Seabronc]

So I put the new computer in yesterday, hit the key, and she fired up! She ran like a champ for a few minutes, no misses, no struggling, nothing like that. And then she just quit. Didn't sputter or idle funny or anything was running fine one second, and the next she just died. And wouldn't start again.:***

Does it start again after the engine cools down?

>-

 

[Art5]

I haven't posted in a while, so I'm going to update again. I've been going through this truck and replacing lots of things. So the reason the truck wouldn't run was a bad ground. I had it running and was going around checking the wires, I wiggled one and the truck shut off. So I fixed the ground and then it would stay running but was running really rough. I put a set of fairly new fuel injectors in it that came out of a 351. I made sure they all sprayed. While I had it apart I replaced the coolant temp sensor and the map sensor, and when I put it back together, the truck started with a shot of carb clean and stayed running and sounded pretty good. So I've been driving it to work every day since, but still having problems. So here's what I'm experiencing. First of all, the truck won't start when it's cold without a shot of carb clean. Then it starts, but it runs rough and smokes out of the tailpipes for up to five minutes. Then the motor jumps up to like 1800 rpms, and the truck smooths out and stops smoking out of the exhaust, but still misses occasionally on both sides. Earlier this week I checked all my fluids and I was a quart low on oil, so I added a quart, friday I had to add another half a quart. The truck seemed like it was having issues on friday because the miss that I'm having became much more frequent, and it's on both sides. So I parked it. I compression tested all the cylinders, and they were all between 165 and 180 psi. None of the spark plugs have oil on them I have put 500 miles on them. Oh yeah, I went out and bought a mechanical oil pressure gauge, and installed it. When the engine is hot, the mechanical guage shows 25 psi when i hold it at about 2500 rpm, then when I let it drop down to idle, the oil pressure drops to nothing. I'm curious what you guys think, particularly about it not starting cold, why it would miss like it does, and about the oil pressure issues. Thank you.

 

[Art5]

DANG!!!!

When it wouldn't start do you know if you lost fuel preasure, spark, or injector signal?

Any codes?...Did the CEL come on prior to the engine dying?

What is the CEL?

 

[Art5]

Does it start again after the engine cools down?

>-

Actually now that I've got it running, the only time it won't start is when it is cold. If it has ran that day, it will start on it's own, if it has been sitting overnight it won't start without a shot of carb clean.

 

[Art5]

Sorry about not replying for a while, broncozone for some reason wouldn't let me post anything for the past several weeks.

 

[Seabronc]

BZ was down.