1990 302 running really rough, possible misfire - Ford Truck Enthusiasts Forums

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1990 302 running really rough, possible misfire

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Old 01-06-2008, 02:37 AM
zer0321 zer0321 is offline
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Exclamation 1990 302 running really rough, possible misfire

Okay, I've got a 1990 F-250 2wd. It has the 302/E4OD combo...lately it has been acting up. My issue started out as a small jitter at low throttle which occured mostly at highway speeds (no CEL) to a the situation now, where it feels like it is misfiring constantly whether I'm giving it gas or idling and has a hard time getting up to speed. I checked the codes-

KOEO codes:
11--System OK
32--Running; Continuous memory: (Trucks ONLY): EGR pressure feedback fault (1985-89 models)
41--Running HEGO (HO2S) sensor voltage low / system lean
41--Continuous memory: No HO2S switching detected
95--ENGINE OFF, Continuous memory: Fuel pump secondary circut fault

Things I've replaced recently-
Ignition Coil, New Spark Plugs & Wires, Distributor Cap+Rotor, MLPS Sensor, O2 Sensor, PCV Valve, Air Filter

I've made sure the spark plug wires were installed correctly, I'm pretty sure they are NOT crossfiring.

The misfire seems to get worse as the truck warms up...

any ideas?
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Old 01-08-2008, 09:44 PM
Old_Paint Old_Paint is offline
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Have you checked for vacuum leaks? Lean codes, dead miss, miss worsening after warming sounds like a vacuum leak that is getting worse as metal expands. I had similar symptoms, coupled with 7/8 crossfire. Look in my gallery and you'll see what I found after 3 dealerships couldn't fix my truck.

Even if the plenum gasket doesn't fail to the outside, if it leaks between the risers at the lower intake, you'll get some pulsating vacuum (which will drive the MAP bonkers), and LOW vacuum. Get a vacuum gauge, and disconnect the cannister purge line between the venturis on the throttle body. Connect the gauge, and see if you have at least 18 inches vacuum. These 5.0's don't like low vacuum at all. More importantly, they REALLY don't like pulsing vacuum. You can learn a lot about your engine that the EEC will not tell you with a vacuum gauge. Most vacuum gauges are combination vacuum/fuel pressure gauges, however, DO NOT use your vacuum gauge for pressure tests on a EFI engine. That combination is for mechanical pumps which only deliver about 5 or 6 PSI. The pressure in the rail will be upwards of 30 PSI at WOT (no vacuum), and upward of 40 PSI at idle (full vacuum). You will ruin the gauge if you use it to check pressure in that rail.

To check for leaks, use propane gas, like an unlit propane torch. If you have a vacuum leak, and you get the propane in the right place, the idle will smooth out and speed up.

Item next, just because your cap/rotor/wires are new, does not mean you have GOOD wires/cap/rotor. I've had rotors fail right outta the box within 100 miles. Make sure you have a good quality cap (MSD is working for me, but I still recommend OE Motorcraft parts) and rotor. Do not put Standard or any other cheap off-brand ignition parts on your Ford. It WILL EAT THEM. Make sure to use Motorcraft wires on that engine. I had a brand spanking new set of Accel racing wires fail on me in about 5000 miles. Check for ignition problems by starting the engine in a dark garage. If it's leaky wires, or loose wires, you'll see it. Make sure all the wires are securely down on the plugs and at the cap. You say they're routed right, but make absolutely certain 5 and 6 stay between 7 and 8 as long as possible. Keep 7/8 as far apart as possible, as long as possible, from the dizzy to the plugs. When you drop #7 down to the plug, make sure it crosses #8 at a right angle. (like a +)

The 95 can be caused by someone running a fuel pump test from the DCL. Did you do that, or has a dealer done it in the past? You have a lot of codes there, and to make sure that you ahve accurate codes, you should clear them first, and start from scratch. Having the 11 first sort of indicates there are no current sensor problems. The others are stored codes, and there's no telling how long they've been there. My 5.0 was spitting 11's at me, KOEO and KOER, but running like poopy. That's when I bought my vacuum gauge, and found the real problem. Any time you run a fuel pump test from the DCL, you WILL get a 95. That's a guarantee. The EEC senses zero voltage at the output for the fuel pump relay when it should be off (12V), because of grounding it from the DCL. When you test from the DCL, you bypass the output of the EEC, and it gets a little upset about something else controlling the fuel pump. Not a big problem. Start a KOEO, and when the codes start flashing on the CEL, pull the jumper to reset. You do not have to disconnect the battery to clear codes. Then, warm the engine, and check codes again. Don't even bother checking codes on a cool engine. You'll get a book full of 'em.

The 32 will be EVP on your truck as well, not pressure feedback. Either it works, or it doesn't work. Clear the codes, and check it again. If the 32 comes back, you'll need to check the EVP on top of the EGR valve. If that's been changed, and you don't have the right one installed, that too will throw a code. There are two versions of the EVP. A grey one, and a black one. I think your '90 should have the black one, but I won't swear to that.

Check the wires/cap/rotor/coil in a dark room first, then put a vacuum gauge on it and see what that tells you. Check back in when you've done that, and we'll see if we can help you out.
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Old 01-09-2008, 09:11 AM
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Conanski Conanski is offline
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Fix your EGR problem first, clear codes and test again. My guess is the lean condition will be gone.
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Old 01-21-2008, 06:01 PM
zer0321 zer0321 is offline
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Okay, so I replaced the EGR valve (re-used the EVP sensor) and It is still doing the same thing, now I'm only getting code 33 after it warms up?
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Old 01-24-2008, 01:41 AM
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Okay, I finally got this one figured out. There was a partially melted vacuum line going to the EGR Vacuum Regulator causing a vacuum leak. It runs much better now that I replaced the leaking vacuum line, but not quite 100%- more like 95%

I found another issue- the spark plug wires I just installed were crossfiring in quite a few places. With this remedied, the truck runs like new again....Thanks for all the help!
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