Engine 1990 Fox wont rev over 3500 RPMS

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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,174
12,091
224
Massachusetts
Those aren’t the right spark plugs for those heads, they will thread in, but look at the difference in thread lenght. The autolite 25s are likely not sitting deep enough into the chamber, if they even fit properly.

please pay attention here. This is important for you to realize. It appears very likely your car has had the long block from a non-HO 5.0 swapped into it. This is due to the incorrect firing order and the incorrect heads. This combo of parts is found on common passenger car engines like a crown Vic or an ‘88 thunderbird. It’s possible the upper intake manifold; and throttle body are also from the same non-Mustang car, but we haven’t gone searching for casting

if you borescope the cylinders, you’ll prob see the Pistons lack valve reliefs.

As you proceed with troubleshooting the car, keep that in mind. It may change the parts you end up using, like spark plugs, or it may present as evidence that the previous owner hacked the car together to kick it off to the next owner.
 
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AydenTv

Member
Nov 19, 2020
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Alabama
Those aren’t the right spark plugs for those heads, they will thread in, but look at the difference in thread lenght. The autolite 25s are likely not sitting deep enough into the chamber, if they even fit properly.

please pay attention here. This is important for you to realize. It appears very likely your car has had the long block from a non-HO 5.0 swapped into it. This is due to the incorrect firing order and the incorrect heads. This combo of parts is found on common passenger car engines like a crown Vic or an ‘88 thunderbird.

if you borescope the cylinders, you’ll prob see the Pistons lack valve reliefs.
i actually went with the cheaper motorcraft ones but ima go outside right now and pull a plug really fast and see exactally which kind i have and take a pic of one right next to an old one which was in the car when i got it and both are same thread length.. i have said this before im not a mechanic and if it fr dont require money im willing to try anythij ng but will also say this the further you dig into this car the weirder it gets.. like example it wants to hook like way too good.. may be the tires or the aod cuz im use to t5s but it will launch for a mustang
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,174
12,091
224
Massachusetts
Well with E6 heads it’s likely down on power. Those heads were pretty weak. Non-Ho 302s were typically in the 180-200HP range. Throw an AOD behind that and it’s down on even more power.

what exactly is wrong with the car? This thread has gone all over the place.

take a photo of the spark plug hole with the plug removed. I can tell from the thread hole depth which plug it will need. But seeing as it is an E6, that info is already known
 
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AydenTv

Member
Nov 19, 2020
63
1
18
30
Alabama
iyWell with E6 heads it’s likely down on power. Those heads were pretty weak. Non-Ho 302s were typically in the 180-200HP range. Throw an AOD behind that and it’s down on even more power.

what exactly is wrong with the car? This thread has gone all over the place.

take a photo of the spark plug hole with the plug removed. I can tell from the thread hole depth which plug it will need. But seeing as it is an E6, that info is already known
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,174
12,091
224
Massachusetts
You're last message didn't post.

More info if you want to identify parts. The upper intake on the 5.0 HO and non-HO differs as well. It's possible the HO intake was installed though as the lowers are the same but the upper is different.

Easiest way to tell is to remove the intake plate. Under the plate, you will see the HO cast into the manifold. If this is missing, it's not the HO intake.
06FCAC92-F68F-4C31-96F6-6631B904DB9F.jpeg



Part number for an 1989 HO upper intake is RF_E8ZE-9425-E4A. The 1990 HO intake started with an F0ZE part number.
93107D58-8B6A-4D67-90E9-116DDB455EE6.jpeg


Other info on what should be on the car

Upper intake: RF-E8ZE-9425-E4A
EGR spacer: E7ZE-9H474-AC 62mm TB side/64mm manifold size
TB: E7SE-HB (stamped on lever) 60mm

That's what should be on your car. You can compare to see how it matches. If the sizes differ, or the part numbers differ, then it's a good sign there are more non-HO parts on your car. I beleive the upper intake manifold part number for a non-HO is RF-E6SE-9425-



Just to be clear on the implications of this. It does appear that in some point of your cars life, the original engine was removed, and the long-block of a non-HO engine was installed. The reasons for this are unknown, but someone did repin the ECU to make it work along with most of the correct parts needed to get it running well. Maybe it was done out of necessity (the only long block they could afford) or maybe it was done to flip the car as cheap as possible. If it was known, it should have been revealed to you. WIth the E6 heads and non-HO cam and possible other non-HO parts, your engine might be making 180-200HP rather than the 225HP it should be making. E6 heads also tend to fall out of steam at higher RPM. They typically offer good low end torque, so they feel peppy on the street.
 
Last edited:

AydenTv

Member
Nov 19, 2020
63
1
18
30
Alabama
You're last message didn't post.

More info if you want to identify parts. The upper intake on the 5.0 HO and non-HO differs as well. It's possible the HO intake was installed though as the lowers are the same but the upper is different.

Easiest way to tell is to remove the intake plate. Under the plate, you will see the HO cast into the manifold. If this is missing, it's not the HO intake.
06FCAC92-F68F-4C31-96F6-6631B904DB9F.jpeg



Part number for an 1989 HO upper intake is RF_E8ZE-9425-E4A. The 1990 HO intake started with an F0ZE part number.
93107D58-8B6A-4D67-90E9-116DDB455EE6.jpeg


Other info on what should be on the car

Upper intake: RF-E8ZE-9425-E4A
EGR spacer: E7ZE-9H474-AC 62mm TB side/64mm manifold size
TB: E7SE-HB (stamped on lever) 60mm

That's what should be on your car. You can compare to see how it matches. If the sizes differ, or the part numbers differ, then it's a good sign there are more non-HO parts on your car. I beleive the upper intake manifold part number for a non-HO is RF-E6SE-9425-



Just to be clear on the implications of this. It does appear that in some point of your cars life, the original engine was removed, and the long-block of a non-HO engine was installed. The reasons for this are unknown, but someone did repin the ECU to make it work along with most of the correct parts needed to get it running well. Maybe it was done out of necessity (the only long block they could afford) or maybe it was done to flip the car as cheap as possible. If it was known, it should have been revealed to you. WIth the E6 heads and non-HO cam and possible other non-HO parts, your engine might be making 180-200HP rather than the 225HP it should be making. E6 heads also tend to fall out of steam at higher RPM. They typically offer good low end torque, so they feel peppy on the street.
ok sorry been busy past few days but this is all great info and i got under the car and started to dig around even brought a good wire brush and stuff to get some cakee up oil and see parts numbers clearly... and i have learned that the fords parts code system likenE is for 1980s decade.. then the year and is mustang etc.. well tldr.. motor mounts look untouched.. like inches of crude thats as old as i am..lol born a year after this model... also got some money and time to kill.. got intake manifold gasket kit, plug wires, valve cover gasket, permatex, 8.8 rear end gasket and 75w 190 gear oil, and a timing light.. well i never used one.. till yesterday.. but my feeling the engine and ear was right..12 btdc tps is at .998... and i replaced coil with a spare one i had previously tested.. cleaned up engine bay even more took apart most of dash gonna replace heatercore nd radio isnt working again.. bad grounds i nelieve.. wiggling the radio ground to dash frame behind the radio.. changes idle... ive had random fuses blow before my headlight switch sometimes needs to be wiggled to have running lights and headlights on at same time.. when i cleanedbthe engine bay yesterday i cleaned off battery to side of motor ground.heard a noise like a snap looked at wire.. looked fine.. and hours later after i took pics and cleaned car.. ita acting up bad again.. idles fine.. 900 rpms.. will idle all day.. but go to take off.. even with a lil throttle it is acting like its out of gas.. well gas station is like 1 mile away so i madenit in 5 cranks lol filled it up (held 4 gallons) with regular unleaded.. barely made it back home..
things to note.. pcv valve screen is prob clogged.. and i found another vac leak on pcv hose to pcv valve.. my charcoil can is dleleted along with egr valve.. the egt is still there and pluged into plug but i capped vacc hose and taped the back holes for security.. and now thinking its either the pcv, it having not enough gas ventilation so i loosened cap..the grounds prob are "thr issue... and here are pics
 

AydenTv

Member
Nov 19, 2020
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passenger lock says e3 so to an 83 something besides standlg
 

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AydenTv

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kk
 

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alex.sweitzer

Member
Oct 27, 2020
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Installed a wideband to monitor AF. When under load, it hangs out in the mid 14s and then right at ~3500 rpms, boom high 24s on the gauge and falls flat on its face. Almost seems like something is just turning fuel off completely.... any thoughts?
 

Trogdor

Member
Aug 30, 2018
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Anna, TX
Installed a wideband to monitor AF. When under load, it hangs out in the mid 14s and then right at ~3500 rpms, boom high 24s on the gauge and falls flat on its face. Almost seems like something is just turning fuel off completely.... any thoughts?
It could still be spark. The wideband will read lean if there is no combustion occurring. Did you put a timing light on it with the spout connected and rev it up to see what the reading is?
 

alex.sweitzer

Member
Oct 27, 2020
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Can’t seem to get an accurate reading on timing with the spout in going through RPM range but it’s easily evident that it is pulling timing, just at this point not sure how much
 

Trogdor

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Aug 30, 2018
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Anna, TX
Can’t seem to get an accurate reading on timing with the spout in going through RPM range but it’s easily evident that it is pulling timing, just at this point not sure how much
With the key on engine off do you see 12v at the third wire from the top of the TFI connector on the distributor? That wire should only see 12v while the engine is cranking.
 

alex.sweitzer

Member
Oct 27, 2020
15
2
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23
Centreville, MD
With the key on engine off do you see 12v at the third wire from the top of the TFI connector on the distributor? That wire should only see 12v while the engine is cranking.
Third wire from the top is reading 4.8V with Key on engine off. This is the red and blue wire going into the distributor.
 

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Trogdor

Member
Aug 30, 2018
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Anna, TX
Third wire from the top is reading 4.8V with Key on engine off. This is the red and blue wire going into the distributor.
That wire should only have voltage when the starter is engaged. It allows tining to be pulled while cranking to make it easier to start. If it has voltage while the engine is running timing will be pulled. I had this issue on my car, so I cut it 2-3 inches from the plug and using another piece of wire I extended and tied it into the red and blue wire on the starter solenoid, the little one that is on the small post in the top. Once I did that all my problems went away. I'll find the short when I replace the heads, cam and intake.
 

alex.sweitzer

Member
Oct 27, 2020
15
2
13
23
Centreville, MD
That wire should only have voltage when the starter is engaged. It allows tining to be pulled while cranking to make it easier to start. If it has voltage while the engine is running timing will be pulled. I had this issue on my car, so I cut it 2-3 inches from the plug and using another piece of wire I extended and tied it into the red and blue wire on the starter solenoid, the little one that is on the small post in the top. Once I did that all my problems went away. I'll find the short when I replace the heads, cam and intake.
Ding Ding Ding we have a winner! I had a couple free minutes and there we go, rolled straight through 3500 rpms. Same issue though, as I can’t seem to find where the short is but for now this will do just fine.
Thank you to all that have weighed in on this lovely adventure! Now we can get back to putting the fun parts on the car!!
 

Trogdor

Member
Aug 30, 2018
34
21
18
43
Anna, TX
Ding Ding Ding we have a winner! I had a couple free minutes and there we go, rolled straight through 3500 rpms. Same issue though, as I can’t seem to find where the short is but for now this will do just fine.
Thank you to all that have weighed in on this lovely adventure! Now we can get back to putting the fun parts on the car!!
I'm glad it got figured out! Please post up if you ever find where the short in that wire is as most likely it will be where mine is.