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85 won't idle runs rough

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donaldb

85 won't idle runs rough

I finished changing the timing chain cover and added a speedi sleeve to the harmonic balancer to fix some leaks. After finishing and taking a test ride everything was fine until about 5 miles from the house. It would surge and sounded like it would back fire through the carb. Wouldn't idle and hard to start. Any thoughts if this is the Duraspark unit or??

Thanks for any input.

1985 351W carbed and C6.

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 85 won't idle runs rough

Administrator

Sorry for the late response. Have you tried it after it sat overnight? Electrical problems, like the pickup in the distributor or the DS-II box, usually correct themselves when they cool off - until they get hot again. And your description of the symptoms do seem to fit with ignition problems.

Having said that, the trouble is usually associated with the last thing you touched. But in this case it doesn't seem likely since it ran fine for 5 miles. And just changing the timing chain cover and adding the sleeve shouldn't make a problem - at least not one with those symptoms.

Any chance you ran out of gas?

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

donaldb

Re: 85 won't idle runs rough

Yeah finally got out to look at it after the snow stopped. Won't idle still. What are the the symptoms of a bad box? Does it go out completely or will it let it run at high RPM, with a miss. If that isn't it, it may be something more dire, cause it sure has a bad miss.

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 85 won't idle runs rough

Administrator

There are two electronic parts that are possible failure points on your truck - assuming yours is the 5.8HO.

So, let's start there. Your signature says "5.8W", but there were two of those in '85 - the 2v version with a computer controlling ignition timing and, to some extent, air/fuel ratio. And the HO version w/a Holley 4bbl and a DS-II ignition box, which has a blue grommet where the wires exit.

Which setup do you have? And when we get that figured out you should consider upgrading your signature so we don't have to do this again.

And, with that answer we can delve into what's wrong.

Gary, AKA "Gary fellow": Profile

donaldb

Re: 85 won't idle runs rough

Thank you Gary, its a 4 barrel HO, and I updated my signature also.

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 85 won't idle runs rough

Administrator

Ok, that simplifies things. And, we won't have to ask next time.

So a hard-starting problem or a poor-running problem can be either ignition or fuel. Let's take fuel first. Check for fuel in the carb by pulling the air cleaner, climbing up and peering down the throat of the carb, and opening the throttle - with the engine OFF. You should see two streams of gas shoot into the carb. If so, you have fuel. If not, we need to diagnose why you don't have fuel.

Also, with the cold weather, is your choke coming on? You should have had to open the choke with your left hand to see the two streams of fuel when you opened the throttle with your right hand. If the choke wasn't closed we have a problem.

Now for the electrical side, assuming you have fuel and choke. The easiest thing to do is to check that you have spark. Pull the coil wire out of the distributor's cap and put it close to a ground and crank the engine. Do you have a hot, blue/white spark?

If not, we need to diagnose what's wrong with the ignition. The HO uses the simple DS-II ignition system. And the two failure points are usually the pickup in the distributor and the ignition box itself.
One issue with the pickup is that the insulation on the wires tends to fail and a short develops. So pull the distributor cap and inspect the wires inside the distributor.

That's probably enough for now?

Gary, AKA "Gary fellow": Profile

donaldb

Re: 85 won't idle runs rough

Yes thank you Gary, everything is good on the fuel side so I'll start on the electrical.

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 85 won't idle runs rough

Administrator

Don't be so sure. Did I fail to tell you about my favorite part of a Holley? The power valve?

The original Holley design was flawed, and yours is one of those if it is the original 4180C that came with the truck. The power valve, which is a fabric valve that controls the amount of fuel going in to the air mix, is easily blown in those carbs. (Holley later added a check valve that should have been there all along.) Just one backfire through the carb will frequently do it, and from there it runs horribly. It can be so rich it doesn't want to start if the choke is on, and it'll be so rich if it starts it'll water your eyes. Idle? What's that - it doesn't want to do it.

So, you still may have fuel problems. One way to test that is to prop/tie the choke open and see if it'll start. It may take some stabs with the throttle, but it should start with all the extra gas. If so, how does the exhaust smell? Can you drive it?

Gary, AKA "Gary fellow": Profile

donaldb

Re: 85 won't idle runs rough

Well I just got in from working on it. The more I work on it the more it seems to be a fuel issue. It has a new Holley on it so I don't think its the power valve. The carb is probably 500 miles old. What I've found as long as you keep the choke on it's ok, as soon as the choke starts to release it starts to give up. I found a pretty bad rubber line to the mechanical fuel pump and replaced it but still no difference. Guess the next is to isolate the fuel tank and get a fuel pressure gauge?

This is my first Ford is the distributor cap supposed to be so loose?

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 85 won't idle runs rough

Administrator

I had a similar problem several years ago that turned out to be fuel hoses. There are short hoses between the fuel tank and the hard line, and from the hard line to the fuel pump. And, if you have dual tanks, hose from the hard line to the switching valve and from the valve to the front hard line.

In my case the hose didn't like the new gas with ethanol and it was leaking right through the sidewall - leaking gas when stopped and leaking air when running. The air killed the fuel pump's vacuum after it ran for a while, and replacing the lines fixed it.

But, yours may be a vacuum leak. If you have a hose off to the intake manifold, or a blown brake booster, you could be sucking lots of air. That makes the air/fuel ratio very lean, and the engine doesn't want to run. However, with the choke on it will run.

So, before thinking about a fuel line problem or a weak fuel pump, you could look for a vacuum leak. Put a hose to your ear and poke around with the engine running and see if you can hear a hiss. Spray brake cleaner around and see if the engine starts running faster.

Gary, AKA "Gary fellow": Profile

grumpin

Re: 85 won't idle runs rough

In reply to this post by donaldb

donaldb wrote

Well I just got in from working on it. The more I work on it the more it seems to be a fuel issue. It has a new Holley on it so I don't think its the power valve. The carb is probably 500 miles old. What I've found as long as you keep the choke on it's ok, as soon as the choke starts to release it starts to give up. I found a pretty bad rubber line to the mechanical fuel pump and replaced it but still no difference. Guess the next is to isolate the fuel tank and get a fuel pressure gauge?

This is my first Ford is the distributor cap supposed to be so loose?

If it is the stock distributor, the cap should be held in place by the straps, and I don't think it should be loose.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

donaldb

Re: 85 won't idle runs rough

Turned out to be the Duraspark unit. Thanks for all your input.'

Donald

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 85 won't idle runs rough

Administrator

Glad you got it figured out. Thanks for letting us know.

Gary, AKA "Gary fellow": Profile