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

lepryy

Member
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!
 
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Noobz347

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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!

Can you get to do the same thing in 4th or in 3rd with enough throttle applied? Does it seem RPM or torque dependent?

What was going on when you first noticed it?
 

lepryy

Member
Jun 4, 2016
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North Carolina
Can you get to do the same thing in 4th or in 3rd with enough throttle applied? Does it seem RPM or torque dependent?

What was going on when you first noticed it?
Yes I can make it do it a little bit in 3rd, 4th, and especially 5th.

And maybe I would say more torque dependent? I really don't know. It's almost like it's lugging but much much worse. Like I said, higher RPM's makes the insane shaking and popping stop, but you can still feel it's not running right at all.

I first noticed it driving to work about 2 months back. It's basically my daily, so I had driven it home from work the night before with not issue. Hopped in around 7 AM the next day and I thought my :leghump:ing wheels were going to fall off it was shaking so bad. Scared me so much I turned around and got in my mom's GT.
 

General karthief

wonder how much it would cost to ship you a pair
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Keep an open mind here. You may have two problems. I would check the drive shaft and the rear suspension, that's pretty rough on the drive train.
also that mechanic with all the mustangs? Are any of them running? Block off the egr? That's not gonna solve anything.
if the air pump is disconnected the cats may be clogged,
how long have you owned the car? Are there any modifications to it?
 

91GTstroked

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Jun 14, 2007
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My 90 coupe has similar symptoms. I recently bought the car in May. Only does it at low rpms (1500 rpms or less) in high gear. I can get it to shake in 4th and only sometimes in 3rd. But it's worse in 5th gear.

I've changed plugs, wires, coil, distributor cap, fuel filter, fuel regulator, and u joints. Checked tps voltage set it to .98 and verified timing which is at 12 degrees.

I had a mechanic friend drive the car and he said I'm lugging the motor. I'm running 3:55 gears and he said the motor likes the higher rpms. He mentioned going with a steeper gear.

I'm just not sold on it though. My old stock 92 coupe never did it. It's quite annoying, but I've learned to drive around it.

If you find out the cause please share. I'm still tinkering on mine.
 

General karthief

wonder how much it would cost to ship you a pair
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Ok, lets try something.
hook a volt/olm meter on the tps, koeo watch the meter as you move the throttle very slowly. The reading should rise steady without jumping around, pay attention just off idle that would be in the rpm area that the car bucks around. I had a simular problem in the 1500-1800 rpm and it was a bad tps, the readings in that area would bounce back to 0 and would not hold a steady volt reading.
 

jrichker

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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?
 

91GTstroked

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Ok, lets try something.
hook a volt/olm meter on the tps, koeo watch the meter as you move the throttle very slowly. The reading should rise steady without jumping around, pay attention just off idle that would be in the rpm area that the car bucks around. I had a simular problem in the 1500-1800 rpm and it was a bad tps, the readings in that area would bounce back to 0 and would not hold a steady volt reading.

Wouldn't the problem happen while in neutral too? What if it's only with a load on engine, meaning driving the car?
 

Noobz347

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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:

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.


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.
 

Mustang5L5

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This is a good one. Looks like you are misfiring or dropping some cylinders under load. I've driven on a dead cylinder, and with only 7 firing the car still makes power, so i'm assuming you've lost 2 here...possibly HG popped between two cylinders and the issue appears under load?

Anyway, you performed the idle reset, but didn't clear the ECU. You should do this. Set the TPS to ANY value within 0.5-1.25 volts, and then check for full sweep and exceeding 3.5 volts at WOT. If it does clears this. set your idle RPM, and then disconnect the batter for 30 mins.

After this, go for a drive. Come back and pull codes. You'll want to run engine off, and engine running codes and THEN run the cylinder balance test. Report what you get.

You didn't need to delete the EGR. In fact, on a mostly stock car it can sometimes be more trouble than it's worth.

You may want to do a compression test here as well. Pull the plugs and have a look. While this may be sensor related, it could also be mechanical.

With speed density cars, the MAP sensor is probably the most important sensor. It looks at manifold pressure and adjusts fuel trims accordingly. Under load, the pressre in the manifold can change which needs to be properly read by the MAP and translated to the ECU. If this sensor is failing (not enough to trigger a code) or a bad vac leak on the vac port to the sensor, it can cause major issues as well.
 
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Blown88GT

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'88 is speed density, so any vacuum leak will cause big problems.
Mustang5L5 stated it has a MAP sensor, it's actually a BAP sensor. Close, but not identical.
In #6, you found one; you probably have others.
You will need a smoke machine to test for leaks.

Check your motor mounts. If they are original, they are probably shot.
 

Blown88GT

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Speed Density = Manifold Absolute Pressure
Mass Air = Barometric Absolute Pressure.


Unless i'm missing something. It has been a long week :shrug:
You're right. My bad!

Just like the guy in the other thread, OP needs a smoke machine.
 

lepryy

Member
Jun 4, 2016
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North Carolina
Ok, lets try something.
hook a volt/olm meter on the tps, koeo watch the meter as you move the throttle very slowly. The reading should rise steady without jumping around, pay attention just off idle that would be in the rpm area that the car bucks around. I had a simular problem in the 1500-1800 rpm and it was a bad tps, the readings in that area would bounce back to 0 and would not hold a steady volt reading.
Thanks, I will go try this shortly and let you all know what happens.