Engine Engine misses badly during acceleration.. help!

markinms

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Mar 1, 2018
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90 5.0L, EFI, HO Heads, mild cam, AOD trans, A9P ECU. Has had a compete tune-up including new Accel coil & distributor, plug wires and plugs (changed to platinum plugs this time). Timing is set at 12 deg BTDC. Vacuum is at 20 and no leaks detected. Fuel pressure is 39 psi and remains so even when running the engine up to 4000 rpms.

Engine idles ok, hot or cold, but does fluctuate 30-50 rpms. Accelerates pretty well up to 2000 rpms then starts to miss. By the time I get to 3000 rpms the missing/cutting out is pretty bad.

Pulled codes:
KOEO - 81,82, 81,82, 10, 11. Codes 81 & 82 are smog related and are expected.
KOER. 94,44, 94,44. Once these complete I press the accelerator and more testing. This time I get 90,90 (cylinder balance test passes). 94 & 44 are smog related and are expected. What I'm not getting here are additional error codes (yeah!) or a code 11 like in the KOEO test.

I've run through most the troubleshooting checklists I've found on this site.

I'm at at a loss here. Is it possible the Platinum Plugs could be causing this? This is the first time I didn't use stock plugs. The Platinum are supposed to last much longer and since I have to pull the wheel wells on my vehicle to change the plugs I thought it was a big plus.

Any help is appreciated. Thanks!
Mark
 
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markinms

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Update:
Installed a new Throttle Position Sensor. Initially I set the voltage to .98 using the green wire on the connector and grounding to the intake manifold. This is the procedure demonstrated by LMR on one of their how-to videos.

Upon further checking, I find procedures that say I must use the both green wire and ground to the black wire on the connector. So I did. The voltage showed .56. Big difference of .42 volts!

So, is just one or both procedures correct? If just one, which one? Due the huge difference in voltage is it possible I have a grounding issue?

If this indicates a grounding issue, any suggestions where I should starting looking?

Your help is greatly appreciated!
Mark
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Pretty much everything you need to know about the TPS
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
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You should not use vehicle ground and use the sensor ground in the harness instead. You will get a different value. Also, 0.56 volts is an acceptable value. Anthing from 0.5 to 1.25 is within spec as the ECU just uses that voltage as a baseline to set WOT reference.

Accel ignition parts don't have a stellar rep. Some folks have had misfire issues with them from time to time. I myself had a Accel coil cause a misfire above 3000 RPMs that I pulled my hair over over for a year before I found it because there were no codes and i has having trouble troubleshooting the issue. Swapped a good used coil on and the problem went away.

Platnium plugs also seem to cause issues, but I don't think it's the cause here. These 5.0 motors do run noticeably better on copper plugs however, anecdotally speaking.

I'm leaning coil. Do you have one you can try out?
 
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markinms

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Thanks for the feedback!

Great write-ups on the TPS. I did have to drill out the mounting holes to get to the .98 volt reading. I see now that wasn't necessary.

I do have a spare Motorcraft coil that I'll use to replace the Accel coil. Perhaps that will help. I can get back to troubleshooting in a few days.

Once again, thanks!
Mark
 

markinms

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Mar 1, 2018
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Finally able start troubleshooting again. Replacing the coil did not help. Going to move on to checking plugs & plug wires.

I'm currently running MSD Street Fire plug wires. I'll pull the wires and ohm check each wire for resistance. If I run into some issues, I'll replace the wires.

I'm currently running Autolite Platinum Plugs. First time I've gone with these. I'm going to go back to original style plugs. Parts store sold me "Autolite 25" spark plugs stating these were what was originally installed in the 1990 5.0 Mustang. Is this true?

Anyway, just a short update.
Mark
 
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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Parts store sold me "Autolite 25" spark plugs stating these were what was originally installed in the 1990 5.0 Mustang. Is this true?

They are equivalent, but technically not true. The OE plugs were Motorcraft SP450's which are discontinued and replaced with SP-450A
 

jrichker

StangNet's favorite TOOL
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lowendmac.com
90 5.0L, EFI, HO Heads, mild cam, AOD trans, A9P ECU. Has had a compete tune-up including new Accel coil & distributor, plug wires and plugs (changed to platinum plugs this time). Timing is set at 12 deg BTDC. Vacuum is at 20 and no leaks detected. Fuel pressure is 39 psi and remains so even when running the engine up to 4000 rpms.

Engine idles ok, hot or cold, but does fluctuate 30-50 rpms. Accelerates pretty well up to 2000 rpms then starts to miss. By the time I get to 3000 rpms the missing/cutting out is pretty bad.

Pulled codes:
KOEO - 81,82, 81,82, 10, 11. Codes 81 & 82 are smog related and are expected.
KOER. 94,44, 94,44. Once these complete I press the accelerator and more testing. This time I get 90,90 (cylinder balance test passes). 94 & 44 are smog related and are expected. What I'm not getting here are additional error codes (yeah!) or a code 11 like in the KOEO test.

I've run through most the troubleshooting checklists I've found on this site.

I'm at at a loss here. Is it possible the Platinum Plugs could be causing this? This is the first time I didn't use stock plugs. The Platinum are supposed to last much longer and since I have to pull the wheel wells on my vehicle to change the plugs I thought it was a big plus.

Any help is appreciated. Thanks!
Mark
High speed miss on a warm engine

Revised 24 June 2019 to add new source & part number for TFI removal tool .

The TFI module mounted on the distributor is one of the culprits for a high speed miss on a warm engine. The other suspect is the PIP sensor inside the distributor. If the problem does not occur when the engine is cold, the TFI module or PIP is definitely suspect. Dumping the codes may help determine which one it is. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

It is not uncommon that the replacement parts may be defective; TFI modules made by non Ford manufactures seem to have a high failure rate.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

10550469_lis_64650_pri_larg.jpg


Lisle P/N 64650

See https://shop.advanceautoparts.com/p...Z0kH8DTh2LmTcgnmc_E4aAuCIEALw_cB&gclsrc=aw.ds

attachments\.586550


diagram courtesy of Tmoss & Stang&2Birds

TFI_5.0_comparison.gif


tfi-module-troubleshooting-gif.586550
 

markinms

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Mar 1, 2018
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Finally, success!

TFI module checked out ok. I ran through the "engine surges at idle" checklist; all components checked out ok.

I ended up replacing the platinum spark plugs with copper plugs (Autolite 25), and found & replaced one bad plug wire. Got everything ready to go, fired her up, and damn; she ran and idled smoother than it ever has. Test drive was great. Smooth and steady up to 4000 rpms (I backed off then) and was up 80 mph in no time at all.

Thanks for all the feedback I got. This is a great forum to turn to when any help or advice is needed!!
Mark
 
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2000xp8

SN Certified Technician
Aug 8, 2003
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Glad you got it fixed.
I think the safe thing to do when tuning up a foxbody is to all real original (as possible) parts.
Motorcraft Cap, rotor, coil, TFI, spark plugs and i've had good luck with ford racing plug wires.
Once you venture into the aftermarket ignition products, things get unreliable.
There is no performance to be had with anything aftermarket either.

I personally have damaged a bunch of aftermarket plug wires, so i'm not a big fan unless it's absolutely necessary for boot angle.
 
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7991LXnSHO

wanna catch the space herp
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They are equivalent, but technically not true. The OE plugs were Motorcraft SP450's which are discontinued and replaced with SP-450A
I used platinum plugs before selling any of them. The electronic ignition is all that is needed to run them. (Points with a hot coil work, but they stay cleaner with Duraspark and HEI.) Replacing the bad plug wire and going through the checklist should have done it. I’d keep a TFI module at the ready anyway.
 
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markinms

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I like the idea of sticking with Motorcraft parts over aftermarket ones. Thanks!

Yep, I do have a spare TFI Module at the ready. Motorcraft item straight from the dealer.

Mark
 

7991LXnSHO

wanna catch the space herp
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I mean this to inform you, not to troll. Motorcraft does not mean Ford made parts. It might mean spec made parts by another manufacturer, often a parts supplier that also is aftermarket (or, gasp, an import, overseas brand factory!). It undoubtedly means re-boxed and re-labeled parts, especially for cars this old. Unless it’s NOS, do not count on it being Ford genuine parts.

“Many times, Ford will approach a contract manufacturer of a particular product (many times a supplier to the company already) and work with them to create a version for sale under the Motorcraft name. These products must meet quality standards set by the Ford Motor Company to be considered for retail sale. Other brands such as Mazda use Motorcraft products in vehicles which both partner when producing. Although Motorcraft can only be contacted through the Ford website, Motorcraft parts and products can sometimes be used on other non-Ford vehicles.”
 

mikestang63

SN Certified Technician
Aug 27, 2012
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I mean this to inform you, not to troll. Motorcraft does not mean Ford made parts. It might mean spec made parts by another manufacturer, often a parts supplier that also is aftermarket (or, gasp, an import, overseas brand factory!). It undoubtedly means re-boxed and re-labeled parts, especially for cars this old. Unless it’s NOS, do not count on it being Ford genuine parts.

“Many times, Ford will approach a contract manufacturer of a particular product (many times a supplier to the company already) and work with them to create a version for sale under the Motorcraft name. These products must meet quality standards set by the Ford Motor Company to be considered for retail sale. Other brands such as Mazda use Motorcraft products in vehicles which both partner when producing. Although Motorcraft can only be contacted through the Ford website, Motorcraft parts and products can sometimes be used on other non-Ford vehicles.”
if I recall,, MSD used to make their spark plug wires. Cardone distributors were the same. Mahle i think made pistons Crane made the Cobra rockers
 
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7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
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if I recall,, MSD used to make their spark plug wires. Cardone distributors were the same. Mahle i think made pistons Crane made the Cobra rockers
Even before buyouts and consolidations, many industries have somewhat incestuous relations, and it is difficult to keep track of who is making what for whom with so many buyouts. @markinms Please buy whatever brand you think will have best QC and stand behind their warranties. Just please do so with your eyes open. We are lucky anybody is making parts in the quantities they do for our cars. The Mustang II guys have it rough.
 
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