Here's an oddball one.

[Tedybear]

Every so often I drive the wife's car to save the gas money.

When I do have to start the BII (which is for about 15 minutes each day to keep the oil in the galleries...other wise I get dry start knocking) It either starts good...and then stalls itself out within a few seconds...It acts like the idle is to low to keep the engine running. Or if I start and drive it daily? It won't stall out.

Now it gets worse depending on the weather. Warm/hot day? It will pop start and while the idle is a bit low? It holds on and runs fairly good. On a very cold day? It starts....and then does the stall out thing.

Now I do tend to over think problems. When the engine is running in closed loop (at temp and after the warm up period is done).. It runs great. Shifts smooth, and holds about 19inches of steady vacuum. (yeah..I'm a geek--there's a vacuum gauge installed next to the ashtray)

Sense this problem happens when it's stone cold start... It seems like it might be either the air intake sensor--or the coolant temp sensor for the computer. If the computer thinks the engine--and the outside air is much warmer then it is? It won't maintain a higher idle during the cold start, and it stalls. The tach kinda reflects this...as it idles lower then it probably should when stone cold.

(The IAC is clean with the ports, and the IAC was replaced not to long ago)

The old girl runs good once it's warmed up. Just that hic-cup first thing in the morning is a bit annoying.

Any ideas?

S-
(computer came up clean--no codes)

 

[Matt77]

intake leak?

 

[Tedybear]

intake leak?

Nope.. (Wish it was..that would be simple)

We did the heads and new intake gaskets when the truck went on the road two years ago. No oddball hissing sounds, and when it's at temp? It's rock solid.

Strange...

S-

 

[adsm08]

What is fuel pressure after it has been sitting?

 

[Matt77]

Vacuum hoses? IAC motor? throttle body? Ignition timer? power brake booster? PCM not detecting it? intake manifold gaskets? Just throwing out possibilities

Matt

 

[Tedybear]

What is fuel pressure after it has been sitting?

That's one I'm going to check when I get my pressure gauges out of storage (family relocated a bit north of town...most of my tools and such are boxed still.)

I know the FPR was replaced 8 months ago. (fuel in the vacuum line, dead giveaway). It did have 34lbs with 20 inches of vacuum on the new FPR...and about 40ish when I removed the hose.

That's the next test. Because it does act like it has low idle when stone cold first thing in the morning---but the stalling out? Does sound like it runs out of gas. (The fuel pump runs all the time it's doing the stalling out bit...but the pump? I've seen pumps run great guns--but the guts are to badly worn out to really function.)

S-

 

[Tedybear]

Vacuum hoses? IAC motor? throttle body? Ignition timer? power brake booster? PCM not detecting it? intake manifold gaskets? Just throwing out possibilities

Matt

Vacuum hoses: checked and good.
IAC motor: Recently replaced.
Timing: Dead on. (that one cost me my timing light...damn cord got caught in the..never mind)
Brake booster: Oddly enough? It had a massive leak a few months ago. The check valve grommet self-destructed. Now that caused massive idle issues.
Intake gaskets: New and correctly installed

PCM not detecting? I'm thinking it might not be reading correct temps and thinking it is warmer then it really is. (problem gets worse the colder it gets)

I'm going to check the fuel pressure as per adsm08--I have the tools and such so it's an easy test. If that checks out? Onward to the next one.

It's not a big of deal...just annoying. I still get decent mileage and it runs like a top once it's in 'closed loop'.

S-

 

[Earl43P]

What is fuel pressure after it has been sitting?

I think what he is getting at is that the pressure is dropping off when it sits.

Prime it a few times before every cold start.
Key on, to Run, no crank.
Wait 3 sec, fuel pump primes.
Key to Off, repeat, repeat, crank.
Enjoy a smoother start, every time.

 

[Tedybear]

I think what he is getting at is that the pressure is dropping off when it sits.

Prime it a few times before every cold start.
Key on, to Run, no crank.
Wait 3 sec, fuel pump primes.
Key to Off, repeat, repeat, crank.
Enjoy a smoother start, every time.

Got it. So the pump might not prime itself up that great for the first start of the day?

I'll give that a shot. I'm driving it to work tomorrow. It's a test run after screwing around with the rear axle seals and bearings. It's had a few short runs around town and to the doc's..It'll be on the interstate tomorrow...(Weeeeeeeeeeeeeeeeee) I figure if the seals hold when I get home tomorrow night? At least that issue is resolved.

This one issue? I'll check that fuel pressure and report back in once I get my gauges out of the bin. Pretty sure first thing in the morning I should have zero, as the system really can't hold pressure that long...(short while? Yeah. Overnight? I'd expect it to drain back). I'll record the numbers as it goes...should be interesting.

S-

 

[adsm08]

Ok, say it sits for 36 hours or more. In a return type fuel system the pressure will naturally bleed out after a while, and is likely to be less than 10 PSI left after sitting for 36 hours. In cold temps like we have this time of year it takes a bit more fuel to keep the engine running. A single priming of the pump may bring the system up to 30 PSI or so. That is the bare minimum it needs to run, and it won't run all that well. If the injectors are releasing fuel faster than the pumps are putting it back into the lines, well it will stall.

 

[fyre82]

Ive been struggling with some similar problems with my '88 Custom.
Finally got it to run and warm up.
Codes indicated Air Charge Temp sensor and Coolant Temp sensor.
I have them and will change them when I get the opportunity as it
finally became winter here in Norcal.

So, you might try pulling codes if and when you can.

Rich

 

[a31ford]

Some where on this forum is the link to what the thermistors that are in the ACT and ECT, I ran across it, but can't remember where.

They are simple 2 wire resistors that change resistance with temperature, most never go bad (MOST....) and are simple to check with a DVM and a known temperature (the list on the forum gave a chart for resistance vs. temp.

I'd check them first, as the ECT is a bastard to get at...

Greg

 

[bobbywalter]

what i am hearing here is it does not stay at high idle for two minutes when cold??..??.


generally thats the ect or act giving a faulty reading and the damn thing thinks its warmed up already. usualy they fail and leave it rich over lean...its rare but happens.

like adsm said...it wants/needs more fuel when its actually cold and if its in a warm idle strategy that will cause stalling. the pump after the first stall should keep up fine but also it should high idle for at least a min or so...

with 19 in of vac i dont think you have a vac problem....

 

[Tedybear]

I managed to "plug" up the vacuum leaks when I redid things a few months ago. The worst one had to be the grommet on the brake booster. It had a small split directly under it, and it wasn't something you'd see. Thankfully it's something you can hear while doing a
wiggle test.

I let it prime several times today. (biting cold with ice and snow/wind). It seems to start---but the idle isn't high enough to keep it running. It just peters out....About 1500 RPM...and just goes down.................in a steady fashion. I'd expect that to happen if this was the middle of summer and all was nice and toasty. But in this crap? I'd think it would stay at about 1500 RPM and stay that high for at least a minute or two...and then dial back...

It's a puzzler. But then again? Once this truck starts and keeps running? Good as gold today. Ran smooth, shifted strong....(once it started and kept running? The idle was high enough for the transmission to slam slightly into drive and reverse....which is what I'd expect this time of year with a higher idle)

I'm still planning on doing a full tune up in the near future. I normally do the full ignition system about once every 2 years. (cap, rotor, wires, and NGK V-Power plugs).

It's so darn cold out now? I might not get to it for a while. It's gotta hit at least 40 for me to use the barn.

S-

 

[adsm08]

Buy better quality spark plugs.