What to try next-erratic engine skip

[gadget73]

if you're swapping ECMs, I'd see about doing a Mark VII ECM and the larger injectors. Probably could use it with that cam and it would be the right firing order.


neutral safety switch does not affect running. The only thing that does is disable the starter relay when its not in park or neutral. It has some marginal tie-in with the ECM for checking codes, but the switch itself can be totally not present and it won't affect how it runs.

could be a fuel pump or ecm relay getting crappy on you and an off/on cycle gets the contacts a little better. Maybe try tapping the relays on the fender while its idling normally and see if it acts up

[Glen]

Is there a choke type thing on a EFI car? It was about 4 deg when I came to work and the car ran like crap. It missed all the way. It seems the colder it is the worse it runs.

[85MercPark]

Bah, switch to a carb or CFI..

<--scurries back in to the corner-->

[cld783]

I have a lopo eec if you want it.

go around and squish the rubber vacuum lines and see if they collapse or are kinked.. especially the one going to your map sensor from the back of the intake. if they are really worn they can suck shut while the engines running.

I also agree with gadget.

[87LongroofCP]

If I were to swap the ecm & injectors from a Mark VII, Wouldn't I run into trouble because I don't have the mass-air? I wouldn't mind doing a mass-air conversion, but I don't know if I could handle the expense and lack the expertice. Who much does that usually run?
I replaced the fuel pump relay last year, and it made no difference. I don't believe there is any choke-type device but I could be wrong. This also happens in the summer months. Thanks

[1987cp]

Mustangs from '86-'88 used the speed-density system. According to my reading, you'll need an ECU from an '87-'88 Mustang or Mark VII (keeping in mind that '88 Mustangs sold in California were mass-air). Any 19 lb/hr Ford injectors should work with the speed-density computer you select. I want to say I've heard of someone getting away with running stock 14 lb/hr injectors with a HO cam and computer ......

And you're correct, SEFI has no choke; startup fuel enrichment and fast idle are handled by the ECU via the injectors and the IAC valve (no "cold start injector" or whatever on Fords).

[87LongroofCP]

I had the upper intake off a couple of months ago, and checked the vacuum lines. They all looked like new, I replaced them all when I did the cam. cld783, what's the ecm out of? I may want it. I guess I should get a map sensor, it's never been changed. Over $55 on the Autozone site? Ouch! I don't mind spending the cash on the parts if I find the cure. I'll have to start making a shopping list for the end of the month, tax time.

[cld783]

I had the upper intake off a couple of months ago, and checked the vacuum lines. They all looked like new, I replaced them all when I did the cam. cld783, what's the ecm out of? I may want it. I guess I should get a map sensor, it's never been changed. Over $55 on the Autozone site? Ouch! I don't mind spending the cash on the parts if I find the cure. I'll have to start making a shopping list for the end of the month, tax time.

speed density 86 crown victoria. send me a pm or something if you decide to ever want it.

[1987cp]

A Vic ECM won't help the situation if he's needing a Mustang/Mark VII setup to match his cam. If I'm not much mistaken, the control module itself very rarely fails, although it's a convenient "black box" to point fingers at when something weird goes wrong. I'd instead try fixing the problem before swapping brain boxes.

I don't *think* the MAP sensor usually goes bad ..... all that 20-year-old wiring can be suspect, though. One (admittedly labor-intensive) suggestion you could run with without getting an EVTM would be to trace all the wires to their source and make sure there's good continuity. I've learned plenty that way trying to replicate various functions on my car after removing the majority of factory wiring underhood.

[87LongroofCP]

Thanks 1987cp Would the mark/mustang have to have the mass air? Forgive my ignorance. I have a lot to consider here. Your point makes a lot of sense. What size are the stock injectors versus the Mark? Thanks

[Pirate]

Having had similar problems before, with a few different Ford products, I would recommend doing the following procedure, to check whether or not the ECM is behaving badly:

While the car is shut off, disconnect the TPS, EGR sensor, and ACT. Try to start the car. If it starts, shut if off, and do NOT turn the key back on for any reason.
If you don't have a code checker, it's now time to buy or borrow one, btw.
Back to the car..
Do not turn the key back on, and now plug in a code checker, and scan for codes, KOEO (key on, engine off). It should read the codes for disconnected parts. If it doesn't, the ECM is bad. If it does, then proceed to step 2.
Connect everything back up, and start the car.
Shut it back off, connect the code checker back up, and scan for codes again, KOEO (above). If you don't get any codes, other than the 'all clear' signal, the KAM (keep alive memory) is dead, and the ECM is dead with it. The KAM is supposed to keep records of codes for 88 ignition cycles. If the KAM is not keeping a record of codes, it's a sign the ECM is on its way out, and this definitely would have been a problem before the engine work.
And to be frightfully honest, you really need to switch to a MK7 LSC ECM and 19-pound injectors, so timing and fuel curves better match the new cam.

[87LongroofCP]

Thanks Pirate, That sounds like a plan. As soon as it warms up a little here I'll do the checking for codes as you suggest. Do I need the mass air for the mark ecm ? Anybody happen to have one?

http://s264.photobucket.com/albums/ii183/87LongroofCP/

[1987cp]

Thanks 1987cp Would the mark/mustang have to have the mass air? Forgive my ignorance. I have a lot to consider here. Your point makes a lot of sense. What size are the stock injectors versus the Mark? Thanks

'89 and later HO engines got mass air. There are new piggyback harnesses you can buy from source such as Summit Racing if you wish to convert without getting salvaged wiring, but getting your ECM from a speed-density car ('87 or '88 non-California) is a simpler approach (especially if not many future upgrades are planned) because you won't really have to change anything other than the computer and injectors.

HO engines used 19 lb/hr injectors; lowpo used 14.

[cld783]

A Vic ECM won't help the situation if he's needing a Mustang/Mark VII setup to match his cam. If I'm not much mistaken, the control module itself very rarely fails, although it's a convenient "black box" to point fingers at when something weird goes wrong. I'd instead try fixing the problem before swapping brain boxes.

I don't *think* the MAP sensor usually goes bad ..... all that 20-year-old wiring can be suspect, though. One (admittedly labor-intensive) suggestion you could run with without getting an EVTM would be to trace all the wires to their source and make sure there's good continuity. I've learned plenty that way trying to replicate various functions on my car after removing the majority of factory wiring underhood.

well yea we've only been trying to explain this to him the entire thread.. he says its been happening even before the cam swap.

i've ran out of ideas at this point and until he swaps out the computer for one of these and a set of 19# injectors, I guess we will never know.

DA1 (1987-88 Mustang)
DB1 (1987-88 Mustang)
DX3 (1987 Mark VII)
VL2 (1987 Mark VII)
DY3 (1988 Mark VII)
D9S (1988 Mark VII)

[87LongroofCP]

Well, that's the plan of attack. Can't do anything untill next week cash wise. Anybody have a Mark VII ecm for sale? Thanks for the help everyone, I'll update as soon as it's changed over.