454 cutting out

[choctawmel]

HELP! The 'Silver Bullet' cuts out. After about 40-50 miles I hit a bump, or even a dip in the road (but not everytime) and the computer 'check' light blinks on/off then the engine cuts out. I've replaced: plugs, wires, rotor, rotor cap, coil, distributor pickup, fuel pump relay, secondary relay, electric Holley fuel pump by the tank. I've cleaned and added ground straps. I've check (hot wired) the ignition switch. I’ve beat, pulled, push, kicked, and shaken on the computer, on the wiring harness, but can’t get it to miss a beat. The EFI guy said it may be vapor locking, to loosen the ‘fuel in’ line when it does it, but that is hard to do going down the road (also could make for FIRE!)
I might add, it hasn’t always done this, just one trip it started. Maybe after the transmission (545 Allison) got over heater, well after I installed the EFI. The engine is 77900 miles old.
mel

[garry]

OH MY this is a tough one.

What is the code stored from the Check Engine light ??

Does cut out = run rough or engine really quits?
Will it start right back up or have to cool down?

If vapor lock the engine will die and then start back up in just a min or so. You can install a temporary shield around the fuel line with extra heave tin foil.

The only hint I see in your post is the 40/50 miles which suggest it is heat related and I would suspect electrical but you have gone through that side pretty well.
Replaced and added ground straps does that mean between the engine and fire wall?

How about the EGR if it is only running rough.

[ronstory]

What year AS?

[choctawmel]

Originally Posted by garry

OH MY this is a tough one.

What is the code stored from the Check Engine light ??
>this I haven't checked. The Turbo City (who I bought the EFI from) guy said it wouldn’t tell me anything.

Does cut out = run rough or engine really quits?
Will it start right back up or have to cool down?
>this is at highway speed, it has never died, it 'cuts out' like for a second, like you turn the key off then on real quick, just like a 'back-fire'

If vapor lock the engine will die and then start back up in just a min or so. You can install a temporary shield around the fuel line with extra heave tin foil.
> I have plastic protector covering the fuel lines from the injector pump (mounted on the frame behind the step) to the throttle body.

The only hint I see in your post is the 40/50 miles which suggest it is heat related and I would suspect electrical but you have gone through that side pretty well.
>These are the ground straps from the engine to the frame, the battery box to the frame, and new battery cables.

How about the EGR if it is only running rough.

I need to check that.

> All the smog stuff came off when I installed the (early 90’s GM) EFI in 2004.
Note: the fuel tank pressures up when driving, but it was (cutting out) doing this while the fuel fill tube was leaking too.
What’s next? Replace the injector pump? Install a fuel pressure gauge? Drop the gas tank and check for trash in the tank?
When I replace the gas filter by the tank I didn’t have a fuel line clamp and I got a gas bath before I could get the line back onto the filter. Which told me: 1)go buy a fuel line clamp, 2)old filter had good flow, 3)don’t do this after a 6-pack.

[choctawmel]

Originally Posted by ronstory

What year AS?

'Silver Bullet' is a 1986 345 with early 90's EFI all GM parts with a wiring harness by Turbo City.
mel

[ronstory]

Cool... early 90's GM EFI. My guess would be a fuel supply issue. I would install the a fuel pressure gauge and check the pressure when you have the issue. I now just buy the cheap Summit Racing brand fuel pressure gauge and permanently mount it all on my my "modified" FUi engines. It's only $20 bucks has saved me lots of time and trouble diagnosing the normal stuff with modified engines.

Also, have you check the prefilter in the tank? If you hit a bump stuff could be collecting around the fuel inlet.

As for pressurizing the fuel tanks... it is normal to have a bit of pressure due to pumpiing back in fuel via return line at 40ish PSI but it should not be excessive. If it is excessive, it can gate the fuel return to the gas tank, which limits the FI pump ability to draw fuel form the gas tank, which causes fuel starvation, which leans the motor which can toss a fault and then the check engine light. Don't ask why I know this.


One last thing... I know it's a dumb thing... but unplug everthing, give it a swab of dielectric grease and plug it in and out a time or two. I've fixed a couple of weird behaviors on a Ford EEC-IV system by doing that. GM has better connectors (weather-pak) but every connector can have a bad day.

Good luck Mr. Phelps.

[HowieE]

Originally Posted by ronstory

One last thing... I know it's a dumb thing... but unplug everthing, give it a swab of dielectric grease and plug it in and out a time or two. I've fixed a couple of weird behaviors on a Ford EEC-IV system by doing that. GM has better connectors (weather-pak) but every connector can have a bad day.
Good luck Mr. Phelps.

If your problem is bump induced I would look for an electrical connection or broke wire.

Dirt in the tank would be all the time once started and would most likely show up as under powered first as the fuel began to be starved off not a sudden cut off. But still install the fuel pressure gauge for future trouble shooting of the fuel system.

If you are setting a Engine Light you should be setting a code. If you can't read the codes take it to someone that can. Do not got to a GM shop go to a private garage.

[Motoman]

ONe poster suggested looking at electrical connections that may be loose; that's one possibility. Another might be the fuel pickup in the tank moving. Does itdo it at all fuel levels or just when the tank is low?

[garry]

IMO it does not sound like a vapor lock normally you have to let it cool and then crank back up also more prone to vapor lock at low speeds.

I also don't think you have a fuel "flow" problem from a restriction but something could be shutting down the injectors or fuel pump.

Did you add any glass fuses when you upgraded to EFI? I have seen fuses that would bounce "open" and fuse looks OK(very hard to find). I assume the EFI is throttle body injection check the wires going to the injectors very carefully.

So hard to diagnose has to be fuel or electric but which one???????

FWIW my guess would be electrical based on the fact the engine has to heat "and" a jaring motion before the problem shows up.

You will have to trace every wire that you installed for a wire pinched buy a blot or rubbing where it is to tight a loose connection any wire to close to the exaust manafold something along that type of failure. But I bet you already know this.

Garry

[ROBERTSUNRUS]

Hi, I agree with some of the posters that it sounds more like an electrical problem, especially if it happens when hitting a bump in the road. While looking at the wireing in the engine compartment, look for tell, tell signs of Mickey Mouse. [droppings or chewed wire looms] Mice like to have a warm place to live and like to chew on wires. I have seen practically brand new cars and trucks with mouse chewed wire looms. They seem to like the intake manifold area so we have seen lots of injector wires chewed up.

[choctawmel]

Originally Posted by ronstory

Cool... early 90's GM EFI. My guess would be a fuel supply issue. I would install the a fuel pressure gauge and check the pressure when you have the issue. I now just buy the cheap Summit Racing brand fuel pressure gauge and permanently mount it all on my my "modified" FUi engines. It's only $20 bucks has saved me lots of time and trouble diagnosing the normal stuff with modified engines.

Also, have you check the prefilter in the tank? If you hit a bump stuff could be collecting around the fuel inlet.

As for pressurizing the fuel tanks... it is normal to have a bit of pressure due to pumpiing back in fuel via return line at 40ish PSI but it should not be excessive. If it is excessive, it can gate the fuel return to the gas tank, which limits the FI pump ability to draw fuel form the gas tank, which causes fuel starvation, which leans the motor which can toss a fault and then the check engine light. Don't ask why I know this.


One last thing... I know it's a dumb thing... but unplug everthing, give it a swab of dielectric grease and plug it in and out a time or two. I've fixed a couple of weird behaviors on a Ford EEC-IV system by doing that. GM has better connectors (weather-pak) but every connector can have a bad day.

Good luck Mr. Phelps.

First the EGR is there but not connected. I’m sure someone makes a plate/plug for that.
I haven't dropped the fuel tank. I was told to find a vented gas cap, but haven't found one yet. Before I replace the leaking gas tank fill hose I did have a 'water in fuel' problem requiring may bottles of 'HEAT'. I could have trash in the tank. The fuel return may not be big enough. I tied the vent and return lines together for the return from the TB. Replacing that would be a chore.
I did do the unplug/plug, spray with contact cleaner when I was kicking, pulling, pushing everything. I have/had some grease somewhere, I'll try greasing them up.
Think I'll get a fuel gauge. The fuel pressure (in the instructions from Turbo City) should be 9-14 PSI.
Then, maybe when I come back from Texas in March, I'll try and drive into the yard of fumes and drop the tank. Need to replace all the rubber hoses from the tank to the steel fuel lines anyway.
I do know that when I can put 74 gallon in the tank, she wouldn't take off from a stop without cutting out/back firing, but I can't remember if the computer light flashed as it cut-out or not. I guess the computer can sense fuel pressure drop.
mel

[HowieE]

Have you read the CODES yet?

You have an electrical problem and it should show up in the codes. Now that said it may show up as a bad sender for a given code but I would look to the WIREING of the sender that is setting the code before just replacing the sender.

Back firing indicates ignition failure while fuel is still flowing.

[ronstory]

Yes, codes will help. It will help to see if you have a wiring issue or something else that is causing the fault.

[choctawmel]

Originally Posted by Motoman

ONe poster suggested looking at electrical connections that may be loose; that's one possibility. Another might be the fuel pickup in the tank moving. Does itdo it at all fuel levels or just when the tank is low?

With a full tank, but not every bump is it noticable.
mel

[choctawmel]

Originally Posted by ROBERTSUNRUS

Hi, I agree with some of the posters that it sounds more like an electrical problem, especially if it happens when hitting a bump in the road. While looking at the wireing in the engine compartment, look for tell, tell signs of Mickey Mouse. [droppings or chewed wire looms] Mice like to have a warm place to live and like to chew on wires. I have seen practically brand new cars and trucks with mouse chewed wire looms. They seem to like the intake manifold area so we have seen lots of injector wires chewed up.

I've had mice feeding on my house wiring, cars, my tractor and mower. Butr no sign in the AS.
mel

[choctawmel]

Today I looked for a fuel pressure gauge but found only an in-line one. I can't see it going down the road at 60mph, did find one on the internet, but can't get it before I go south.
I check and lubed all the plugs, checked the pins, checked the EGR valve, they want $42 for a block plate, so, sealed it and put it back in.
I'm wrapping the headers just in cast.
I did find the vamuum tube to the MAP to be loose at the 'F Port' on the TB and put a clamp on it.
Also, after 4 years I read the installation instruction again (or maybe for the first time) and noted, "The MAP sensor is installed in the air cleaner or air track ahead of the TB unit." Which it is not. That will be Sunday afternoon job.
Thanks for the contiued help.
mel

[ronstory]

Where is your MAP installed now?

[choctawmel]

Originally Posted by ronstory

Where is your MAP installed now?

cable tied behind the air cleaner housing
mel

[HowieE]

I am going to go back 40 years to a problem I had with a VW. When the engine was hot it would cut out and then go without reason. Spent several days of our vacation in upper New York state until a farmer standing next to me in motor parts suggested the coil. The coil was cracked.

[choctawmel]

Originally Posted by HowieE

I am going to go back 40 years to a problem I had with a VW. When the engine was hot it would cut out and then go without reason. Spent several days of our vacation in upper New York state until a farmer standing next to me in motor parts suggested the coil. The coil was cracked.

I replace the junkyard coil with a new store bought one.
mel