No power, shuddering under load

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Buffalobill
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No power, shuddering under load

Post by Buffalobill »

Got the xr registered a couple weeks ago, ran great. I've got a big r motorsports hybrid turbo, a China header(I know it's going to crack, I just got it for temporary use while my manifold was getting the broken studs EDM'ed out), a kirban adjustable fuel pressure regulator, a walbro 255 in the tank, and 3 inch exhaust from the turbo back. I bumped up the fuel pressure a small amount, around 43 psi at idle with the vacuum port plugged.

Last weekend it ran great, no gillis valve, wastegate dumping at 18 psi. This weekend I fire it up, and it won't run right, like a severe misfire. All the ignition system looked old, so I put in new autolite plugs, new autozone tfi module, plug wires, cap and rotor, and coil. Still nothing.

Fuel pressure still looks good, I changed the fuel filters, it's full of 93 octane.

What are the symptoms of a bad injector?
my8950
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Re: No power, shuddering under load

Post by my8950 »

What kinds of plugs and wires did you use?
What gap on the plugs?
Why change the TFI, and I guess why change the coil too?
James Wieler
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Re: No power, shuddering under load

Post by James Wieler »

How is fuel being managed under boost? The factory FPR has a vacuum hose running to it that senses both vacuum and boost and compensates fuel pressure accordingly. Does your Kirban do the same?
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Buffalobill
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Re: No power, shuddering under load

Post by Buffalobill »

my8950 wrote: Sun Mar 28, 2021 10:21 pm What kinds of plugs and wires did you use?
What gap on the plugs?
Why change the TFI, and I guess why change the coil too?
Autolite plugs, duralast gold wires

.28

Why change the tfi? Looking up similar problems, it seems like a possible solution, especially with 35 year old electrical parts. Same with the coil.
Buffalobill
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Re: No power, shuddering under load

Post by Buffalobill »

James Wieler wrote: Sun Mar 28, 2021 11:23 pm How is fuel being managed under boost? The factory FPR has a vacuum hose running to it that senses both vacuum and boost and compensates fuel pressure accordingly. Does your Kirban do the same?
Yep, it's the kirban adjustable fuel pressure regulator that stinger sells.
my8950
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Re: No power, shuddering under load

Post by my8950 »

Buffalobill wrote: Mon Mar 29, 2021 3:41 am
my8950 wrote: Sun Mar 28, 2021 10:21 pm What kinds of plugs and wires did you use?
What gap on the plugs?
Why change the TFI, and I guess why change the coil too?
Autolite plugs, duralast gold wires

.28

Why change the tfi? Looking up similar problems, it seems like a possible solution, especially with 35 year old electrical parts. Same with the coil.
I guess I would back up and do just one or two.
What number of Autolite? Use only copper plugs, I think the autolites to use are 764 or 109.
I also would use only Motorcraft wires, not only, but I do.

Was the stock fuel pressure regulator bad? If not, I'd also use it.

Parts cannon doesn't usually pinpoint the specific issue, if you changed 10 random things and it fixed the issue, which one was it?
Buffalobill
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Re: No power, shuddering under load

Post by Buffalobill »

my8950 wrote: Mon Mar 29, 2021 6:17 am
Buffalobill wrote: Mon Mar 29, 2021 3:41 am
my8950 wrote: Sun Mar 28, 2021 10:21 pm What kinds of plugs and wires did you use?
What gap on the plugs?
Why change the TFI, and I guess why change the coil too?
Autolite plugs, duralast gold wires

.28

Why change the tfi? Looking up similar problems, it seems like a possible solution, especially with 35 year old electrical parts. Same with the coil.
I guess I would back up and do just one or two.
What number of Autolite? Use only copper plugs, I think the autolites to use are 764 or 109.
I also would use only Motorcraft wires, not only, but I do.

Was the stock fuel pressure regulator bad? If not, I'd also use it.

Parts cannon doesn't usually pinpoint the specific issue, if you changed 10 random things and it fixed the issue, which one was it?
I don't consider a full ignition replacement on 1980s tech components parts cannon. Imo, it's just cheap insurance, and rules out a spark problem. It was going to happen eventually anyway, just like a new air filter and new fuel filters. Would you consider replacing those parts cannon too?

I replaced the fpr because of the bigger turbo so it won't run lean. I know everyone says these cars run rich stock, but I want the ability to adjust the pressure.

I have the autolite 764s, already knew not to get anything else.the old plug wires were not motorcraft, and the cap and rotor were worn.

Now that the ignition system isn't the source of the problem, what are your next thoughts?

The injectors are triggered with a ground interrupt, with constant positive, correct?
my8950
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Re: No power, shuddering under load

Post by my8950 »

Buffalobill wrote: Mon Mar 29, 2021 7:24 am
my8950 wrote: Mon Mar 29, 2021 6:17 am
Buffalobill wrote: Mon Mar 29, 2021 3:41 am

Autolite plugs, duralast gold wires

.28

Why change the tfi? Looking up similar problems, it seems like a possible solution, especially with 35 year old electrical parts. Same with the coil.
I guess I would back up and do just one or two.
What number of Autolite? Use only copper plugs, I think the autolites to use are 764 or 109.
I also would use only Motorcraft wires, not only, but I do.

Was the stock fuel pressure regulator bad? If not, I'd also use it.

Parts cannon doesn't usually pinpoint the specific issue, if you changed 10 random things and it fixed the issue, which one was it?
I don't consider a full ignition replacement on 1980s tech components parts cannon. Imo, it's just cheap insurance, and rules out a spark problem. It was going to happen eventually anyway, just like a new air filter and new fuel filters. Would you consider replacing those parts cannon too?

I replaced the fpr because of the bigger turbo so it won't run lean. I know everyone says these cars run rich stock, but I want the ability to adjust the pressure.

I have the autolite 764s, already knew not to get anything else.the old plug wires were not motorcraft, and the cap and rotor were worn.

Now that the ignition system isn't the source of the problem, what are your next thoughts?

The injectors are triggered with a ground interrupt, with constant positive, correct?
If you're having an ignition problem, I'd only go through one item at a time, rather than changing all at the same time.
Regarding TFI module replacement, is there thermal compound in good shape on the back of the module between the distributor and TFI module?
I can't say that the fuel pressure regulator would be a cause of the issue here, but the stock one works fine, even with a larger turbo.

There are a lot of complaints similar to the issues you're having. Motorcraft wires are cheap insurance to bypass any questionable wires. Even if you didn't have them before, might be worth trying.
Buffalobill
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Re: No power, shuddering under load

Post by Buffalobill »

Tfi module came with new thermal compound.

I don't know if it's a spark or fuel issue, the new ignition components with the same problem lead me to believe it's a fuel issue.

It's at the shop now for a safety inspection, I asked the guy to take a look.

My next idea is to run it at high idle and unplug the injectors, one at a time.
Buffalobill
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Re: No power, shuddering under load

Post by Buffalobill »

Here's another question, how does an engine behave with a stuck open wastegate?
my8950
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Re: No power, shuddering under load

Post by my8950 »

Buffalobill wrote: Mon Mar 29, 2021 11:26 am Here's another question, how does an engine behave with a stuck open wastegate?
If the gate is stuck open, it won't make any boost.

I've had number of the original actuators blow out the diaphragm, this will keep it closed. Exact opposite of what you're asking.
my8950
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Re: No power, shuddering under load

Post by my8950 »

my8950 wrote: Mon Mar 29, 2021 11:32 am
Buffalobill wrote: Mon Mar 29, 2021 11:26 am Here's another question, how does an engine behave with a stuck open wastegate?
If the gate is stuck open, it won't make any boost. It will run and drive the same when in vacuum, so idle conditions and anything in vacuum should be the same, or very close to the same with everything functioning "normal".

I've had number of the original actuators blow out the diaphragm, this will keep it closed. Exact opposite of what you're asking.

Stuck open is a leak, so no boost.
Stuck closed is closed, meaning no leak, so it would overboost if you keep in the pedal.
Buffalobill
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Re: No power, shuddering under load

Post by Buffalobill »

With no boost, is it still drivable?
my8950
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Re: No power, shuddering under load

Post by my8950 »

Buffalobill wrote: Mon Mar 29, 2021 11:56 am With no boost, is it still drivable?
Sure, as long as you have everything else still connected. I wouldn't try to run it with the intake charge piping off.
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Re: No power, shuddering under load

Post by Buffalobill »

Ok, that's what I thought.a friend of mine is convinced that it's the wastegate, it can't be.

I drive a truck for work, it's a high mileage cat c15. Obviously no ignition system. I think it's got fuel issues as well. When it cold, it bucks and shudders like my merk. But it goes away after it warms up. I literally just noticed it this morning. This is why I'm leaning towards the fuel being the issue on the xr. It's like I'm running one cylinder as an engine brake....
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