Engine 1988 LX 5.0 shaking violently and popping under acceleration - video inside

lepryy

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This is ALWAYS the first step in troubleshooting not so obvious engine problems....

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

Did you get the engine running codes?
Yes, in the original post I stated I got codes 33, 44, and 94 during engine running test.
 
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lepryy

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At this point, you should probably run Jrichker's Surging Idle Checklist:


Aside from the jerkiness in the video ( I stated what that looked like to me ), the only other thing that raises an eye in your description is this:




I'm not sure what you mean by this exactly. If your TPS is slotted then it can be adjusted however, slotted/adjustable TP Sensors are not required on Fox Mustangs with an OEM EEC.
I followed this video to a tee: View: https://www.youtube.com/watch?v=T-T0Ry7VmA0


In the video he says if your TPS will not twist far enough to adjust the voltage properly, you can enlarge the screw holes on the TPS body to allow more adjustment. And that's exactly what I did.
 

lepryy

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First thing to do is reset the computer. You changed things that requires it to be done.
I shall do this next. I'm seeing in other posts on this forum that people suggest disconnecting the battery, then turning on the headlights to drain the ECU capacitors or hitting the brake a few times. Or just let it sit unplugged for like 30-45 mins. Or both?
 

lepryy

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You're right. My bad!

Just like the guy in the other thread, OP needs a smoke machine.
How about a big vape? I'm actually being serious unfortunately.
 

General karthief

wonder how much it would cost to ship you a pair
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Do the surging idle checklist, I know you don't have a surging idle but it will help you get it running right, start at the top and work your way step by step. Don't skip around.
 

Mustang5L5

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I followed this video to a tee: View: https://www.youtube.com/watch?v=T-T0Ry7VmA0


In the video he says if your TPS will not twist far enough to adjust the voltage properly, you can enlarge the screw holes on the TPS body to allow more adjustment. And that's exactly what I did.

I like his channel, but disagree with how much he emphasis the TPS.

It’s non adjustable. It takes baseline reading at key on, and anything 0.5–1.25 is acceptable. Once the cars running “adjusting” the TPS is indirectly changing timing which is why the car does change how it runs. Once you shut the car off all of that is lost.

My TPS is set to 0.85 volts or something like that. I refuse to set it at 0.99 out of spite
 
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Mustang5L5

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Left it unplugged for about 1 hour. I took it for a drive around the block and now it's idling super high at about 1500 rpm and still doing the same thing. No change.

I think you have a vac leak.

Unplug the IAC, adjust the screw down to a low idle (barely runs steady) and then unplug the battery.

Then come back and connect it and plug the iac back in. Should idle around 800-900.

If it idles up high unplug the IAC. If it’s still high...vac leak. Time to get the smoke machine
 
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jrichker

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Thanks, I will go try this shortly and let you all know what happens.
AS suggested, a cylinder balance test is recommended...


Cylinder balance test: use this to find dead or weak cylinders:

Revised 09-Sep-2017 Added reminder to write down the stored codes and engine running codes.

The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C, have the clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.


Here's how to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

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If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.
This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you dump the codes and then you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10
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Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader 3145.
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
Order it at Walmart for a better price and free shipping
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Write down the codes that the computer outputs since they will give you information on problems that are stored in the computer's memory


Cylinder balance test


If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1300-1500 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

Warm the car's engine up to normal operating temperature. With the test jumper in test position, start the engine and let it stabilize. It should flash a 10 and then a 4 and maybe an 11. If no 11, then there are other codes that will be dumped.

Write down the codes that the computer outputs since they will give you information that the computer found when it is running. These are often different from the stored codes.

One of the first tests it does is to open the EGR all the way, this will cause the engine to stumble and almost die. If the engine dies here then you have EGR problems.
To start the cylinder balance test, briefly floor the accelerator past 2500 RPM and let off the accelerator. The engine will stabilize at about 1300-1450 RPM and the cut off the fuel injectors one at a time. The engine speed will drop briefly and the computer will turn the fuel injector for the cylinder under test back on. Then it starts the process for the next cylinder. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

See View: https://www.youtube.com/watch?v=HDXrkKS4jTE
for a visual tour through the process. There is no voice narration so you have to listen carefully for the engine sounds. I posted the link for the benefit of Stangnet members who had questions about how to do a cylinder balance test. I do not own that video and I am not the creator.

Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark plug hole. The other type leaks too much to get an accurate reading. Your local auto parts store may have a compression tester to rent/loan. If you do mechanic work on your own car on a regular basis, it would be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the throttle wide open with a plastic screwdriver handle between the throttle butterfly and the throttle housing. Crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.

I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.

A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.
 

91GTstroked

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Can bad motor mounts cause crazy vibration like this only at certain rpms or mph? If put into neutral and revving the engine problem is gone? Only happens in gear?
 

lepryy

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Jun 4, 2016
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Hey everyone, I've been having some very concerning issues with my 1988 5.0.

For starters, the car has completely stock engine internals. Here's a short 30 second clip of the issue I'm having: View: https://www.youtube.com/watch?v=INJaNCEc_aE


The issue is almost always in a high gear running at low RPM. In the video you can see I'm in 5th going roughly 40-45 mph. The car will cruise relatively okay, but once slight throttle is applied, the entire car shakes like it's going to fall apart, has basically no power whatsoever, and occasionally backfires (95% sure it's backfiring through the intake not the exhaust).

This issue began about 2 months ago and completely at random. It got better for a couple weeks but recently it's become so bad I'm worried to drive the car for fear of damaging it.

Here's what I've already done:
  1. Adjusted timing to about right on 12 degrees. I tried to do the factory 10 but she seemed to run much smoother at 12. Previous owner had it at 16 for some reason?
  2. Local mechanic who owns at least 6 foxes suggested to delete the EGR. So I got the block-off kit from LMR.
  3. Visually inspected every spark plug. I did not notice any fouling. Gaps were consistent.
  4. Checked all plug wires. Cylinder #6's wire was reading about 16k ohms. The rest hover anywhere from 9-12k ohms. I replaced the one reading high with another I had of the same length that was reading 8k ohms. There is so much conflicting information out there about checking plug wires I have no idea what I'm doing. If money wasn't extremely tight I'd just order a new set of wires off LMR. But I can't afford to do that and not have it fix the problem.
  5. Adjusted the idle screw. TPS was crazy low (like 0.5 volts), I set it to 0.95. Performed a base idle reset. Didn't do the whole disconnect the battery for 30 minutes part though.
  6. Found the vacuum line that runs from the underside of the upper intake to the charcoal canister was super rotted. Replaced it with some fuel line I had laying around (only temporary but it works for now).
  7. Pulled codes. During KOER test I received codes 44, 94, and 33. I think 44 and 94 may be from my X-pipe that does not have the smog port. The smog pump is still on the car and has a belt on it but no tube to the exhaust. It's been like this for at least 3 years. Also I believe code 33 is EGR related (like I said I removed it) but also my kit came with the little plug that is supposed to tell the computer the EGR is functional. Idk.
That's where I'm at currently. If anything the problem has only gotten worse. I'm literally at a dead end here folks. My car is running like absolute ass and I've already entered it in the Foxtoberfest show. Any help and suggestions would be greatly, greatly appreciated!
Problem solved. Installed new plug wires and the issue disappeared.