Bad miss at 30-35mph

[PushnFords]

Stock '87 CV with 130K except for a high flow fuel pump. I haven't been driving it for long but it has a bad miss at 30-35 and it seems to be getting worse. I don't notice it at speed...took it on a 375 mile trip yesterday and it seemed to run pretty good. No dash lights on...I've ordered a couple of manuals but they aren't here yet...where should I start checking first?

Thanks,

Derek

[johnunit]

plug wires, cap and rotor.

[1990LTD]

If I don't know the history of the car I would say a full tune up and see if your problem still persists.

[Smokestacklightnin]

Dont buy cheap plug wires if you replace them. I bought some from Crap Zone, and they caused me to have a miss. I went to Ford racing wires after that, and wont use anything else. If you replace the cap, get the one with brass terminals instead of the aluminum.

[johnunit]

yeah, should have said that. Ford Racing are generally considered the best value, and brass terminals.

[PushnFords]

Should have added more info...sorry. The plugs, wires, and cap were replaced not long before I got the car. I pulled the plugs last week to check the condition and gap and they were all pretty clean. I didn't ohm the wires but they didn't have any obvious damage. I believe they are Carquest wires. The cap is new but aluminum terminals and has some corrosion starting. I pulled a good used brass terminal cap out of my parts stash yesterday but I haven't had a chance to install it yet.

Would a bad IAC valve cause anything like that? It surged on me a couple of times two weeks ago so I picked up a newer used valve this weekend but I haven't installed it yet.

I have a vacuum leak somewhere too. My auto temp control goes full hot under load. I didn't get a chance to look it over tonight....

[johnunit]

definetely suspect wires and cap if they're no name and corroded.


A vacuum leak can cause all sorts of issues.

[trwp72]

I just replaced my wires, cap, and rotor button... cured my engine miss.... Seemed to start after the engine warmed up... I think a plug wire was breaking down, as the new plug wires finnally cured the problem. The cap and rotor button helped, but it staightened out with the new wires... (Autolite professional series. lifetime warranty...) I want to go to the Ford racing wires next time, does anyone know if they come in grey? Just want the car to look stock... Also, none of the wires looked bad at all... In fact, they all lookd new... but that was definently the problem!

[johnunit]

FRPP wires come in black, but not gray.

[91waggin]

Also, check for codes. Your EGR might be opening at the wrong time.

[PushnFords]

Also, check for codes. Your EGR might be opening at the wrong time.

Will these systems store codes without illuminating the CEL?

[sly]

some codes, yes. the CEL may be burnt out too unless you've seen it come on and go off.

[johnunit]

A fuel filter can also cause weird misses.

In general, you'll want to change the following if you do not know the history of the car for sure:

Plugs
Plug wires (good Ford stuff)
Cap and rotor (brass terminals)
Fuel filter
PCV valve
Air filter
Check base timing for about 10* advanced(spout connector unplugged, vacuum line to distributor pulled and plugged)
I'd also probably seafoam it through the brake booster vacuum line

[PushnFords]

some codes, yes. the CEL may be burnt out too unless you've seen it come on and go off.

The CEL is the outline of the engine on the top left of the CV dash...right? It lights up when I start the car so it should be good. I'll have to see if my code scanner has the adapter to work on the car...otherwise I guess I'll add it to my list of things to buy.

A fuel filter can also cause weird misses.

In general, you'll want to change the following if you do not know the history of the car for sure:

Plugs
Plug wires (good Ford stuff)
Cap and rotor (brass terminals)
Fuel filter
PCV valve
Air filter
Check base timing for about 10* advanced(spout connector unplugged, vacuum line to distributor pulled and plugged)
I'd also probably seafoam it through the brake booster vacuum line

I put a new fuel filter on when I replaced the fuel pump and pinched vent line when I bought the car. The plugs/wires/cap/rotor were all replaced by the PO. I've pulled the plugs to regap them (they weren't gapped on install) and are in good shape. I haven't ohmed the wires but they are visually in good shape and should be decent quality. The cap and rotor are a little corroded but not enough to cause a miss...I have a good used brass terminal cap I'll probably install tonight anyway. The air filter was also replaced recently by the PO...I haven't check the PCV valve but that wouldn't cause a miss anyway.

Right after I got the car I found the vacuum lines going to the park brake release switch were both unhooked...along with the radio's ground wire. Today over lunch I checked the park brake switch and diaphram and they are good so I'm not sure why they were unhooked. I did find out my vacuum can is leaking so I'll see if the local junkyard has a good one tomorrow. The hose going to my MAP sensor is also really soft and may be collapsing...and I can't get to the end under the intake...so I may end up pulling the intake to see how everything looks under there. I also found a thread on here about which switches are for the EGR and which are for the smog pump so my smog pump stuff will soon be coming uff. I spent quite a bit of time already trying to patch together all of the broken lines, swelled ends, etc. Plus some of the metal tubing is rusted out anyway. Fun stuff.

[sly]

yeah... that's the CEL. so yes, the CEL works. There is a way to one wire check the codes and just count out the flashes to figure out the codes... but I don't remember where to connect.