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Speed Density Issues

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Bruno2

Speed Density Issues

I am having issues with a 91 F 150 351W. It seems to act up when it's cold outside. Sort of like the fuel and air isnt mixing right. I know these trucks have an ambient air temp sensor, MAF and a MAP. I believe it is some sort of communication error with the PCM. Is there a procedure to ohm the above sensors out for diagnosis?

Symptoms are hard starts. Truck turns over, but doesnt like to catch and run. When it does finally run it has a horrible idle, smells rich and wants to die at stops.Requires a lot of throttle to clear it out and make the truck go.

Any suggestions would be great.

Whitey: 1996 F 250 XL CCLB 4X4 7.3 DI ZF5 (The Work Horse) Lots of power mods
Whitey Jr: AKA Jr 1982 F 150 CCLB 4X4 351W C6 (Jr Work Horse) respectable power, but not over the top
The Bronco: 1987 Bronco XLT 351W C6 (needs work) Lots of off road mods and plenty of power mods
The Dodge: 2006 Ram 2500 CCSB 4X4 5.9 HO Cummins (The reliable ride that cant keep an AC in itself) (5th AC go around almost complete)

85lebaront2

Re: Speed Density Issues

Administrator

There are resistance values for the sensors, ECT, ACT are resistance, the MAP is a strange one, it generates a variable frequency based on the manifold absolute pressure (amount below atmospheric). FWIW, the ACT and ECT values are the same for a given temperature. Here are the values, if you have a good multimeter you can check the values on the air and coolant sensors.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Bruno2

Re: Speed Density Issues

In reply to this post by Bruno2

So I thought we had it whooped after changing the MAP sensor. Then I decided it was an ignition issue. I put the spark tester on the coil and it was hitting just fine. So it's not the p/u coil or tje ICM.

I guess I need to pull codes now.

Gary Lewis

Re: Speed Density Issues

Administrator

Here's the video Brandon sent me:

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

Gary Lewis

Re: Speed Density Issues

Administrator

That sounds like late timing to me. Maybe the timing chain jumped a tooth?

Gary, AKA "Gary fellow": Profile

85lebaront2

Re: Speed Density Issues

Administrator

I agree with you Gary, definitely sounds like it is quite a bit retarded. Have you tried a vacuum gauge to see what you have for manifold vacuum with it running?

Bill AKA "LOBO" Profile

ArdWrknTrk

Re: Speed Density Issues

Administrator

In reply to this post by Bruno2

Without knowing a thing I replied to Gary's video asking if the truck had good fuel pressure and if the regulator vacuum line was dry.

I didn't get the first impression that the cam timing had slipped. I'm not hearing it spitting back, but that may just be because it doesn't have a carb.

I hope it's a simple fix!

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Bruno2

Re: Speed Density Issues

In reply to this post by 85lebaront2

It looks as though I am 9-10° before TDC WITH 15-16 Hgz of manifold vacuum.

Bruno2

Re: Speed Density Issues

Also, I believe the truck has two fuel pumps(one in each tank) and.it acts the same with either one selected.

ArdWrknTrk

Re: Speed Density Issues

Administrator

Don't you have a lift pump in each tank and a high pressure pump at the reservoir on the driver's side frame?

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

85lebaront2

Re: Speed Density Issues

Administrator

Jim, 1990 and up, a high pressure pump unit (called a Fuel Delivery Module) is installed in each tank. Each has two valves, one closes the high pressure line until the pump is running, the other does the same for the return line.

Bill AKA "LOBO" Profile

ArdWrknTrk

Re: Speed Density Issues

Administrator

Okay. I wasn't sure exactly when Ford went to the FDM's.

I thought it was after the Aeronose but I get it now that it was the Bricknose/Aeronose transition.

The cam chain can be checked for slop by rocking the crank.
Pulling the top end down or even a valve cover on these engines is work.

I have a pretty good understanding of how the FDM's work.
I asked Gary if I could have his dead one to dissect. 🤓

Still... checking fuel pressure is simple.
As would be seeing if it hits on a shot of ether while cranking.
If Brandon has a noid light he could check to see if the injectors are getting a pulse.
(I don't know if the plugs are dry or wet)

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

mat in tn

Re: Speed Density Issues

by all means, check the fuel pressure!
if the fuel pressure does read lower than spec. 35 psi min running /45 psi static not running. then the fuel filter being stopped up is very common. certainly, start there before condemning any mechanical parts. low fuel delivery will keep the injectors from responding well at all.

85lebaront2

Re: Speed Density Issues

Administrator

mat, go back and look at his frequency on the MAP sensor and see what that tells you against the table I posted.

Bill AKA "LOBO" Profile

mat in tn

Re: Speed Density Issues

i may just be tired but i do not see "his frequency" in order to compare. I did wonder about another point though. is the timing which was claimed 9-10 degrees with the spout removed? if not then it seems low

mat in tn

Re: Speed Density Issues

also, we are talking about ignition timing yet if the chain has enough play then it will be valve timing too of course. and compensating the ignition does nothing for the valve timing. this is assuming only slack and not jumped time which is an extreme. how many miles are on this chain is a big point. i generally call it on a chain around 150k for slack alone. it's cheap insurance for a mechanic. some may say "life of the engine" is what you should expect from a chain. I just don't take the risk .

85lebaront2

Re: Speed Density Issues

Administrator

In reply to this post by mat in tn

Sorry, He sent that to me on FB, he had a 15-16 Hz frequency at idle which extrapolates to well over 30 in of vacuum. Even in space I don't think that is even possible.

On most of the EFI Fords I have worked on, 10° BTDC is static setting with the SPOUT disconnected. 9-10° is close enough to run reasonably.

Bill AKA "LOBO" Profile

ArdWrknTrk

Re: Speed Density Issues

Administrator

In reply to this post by ArdWrknTrk

The first post (back in October) does have the symptoms of a clapped out timing set.
I came here from the video and didn't see the posts above that.

It seems he says 15-16 in/Hg manifold vacuum. Which is not good.... not terrible.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

ArdWrknTrk

Re: Speed Density Issues

Administrator

In reply to this post by 85lebaront2

If Brandon replaced the MAP sensor and is still seeing a reading off the charts low, perhaps he should find a 'shop' with an old school Rotunda tester or just pitch it in the bin?

I'd take a scope and feed the pcm what it expects and see if the truck starts and runs.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

mat in tn

Re: Speed Density Issues

In reply to this post by ArdWrknTrk

a fair "old school" test would be to lift off the dist cap with the damper set on 0 tdc and mark the rotor location with a sharpie on the cap base. then see how much play is in the chain from there. all the play that can be found this way is the amount which the ecu is having to deal with also. this seems like a foundational part of the problem solving to me. again, the mileage on this chain can be a major clue.

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