Stumbling at 3k +

gdushkin

New Member
Nov 6, 2019
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I am having some stumbling at high rpms. The car starts jerking pretty hard once it passes 3,4k.It idles well . I have rebuilt the engine it pretty much stock except for longtube headers x-pipe and a bbk cold air intake. I have replaced maf, put in a better fuel pump, fuel tank , ignition coil, wires spark plugs, 02 sensors and some other minor parts. I have recently purchased a remanufactured ecm due to the old one having some water damage, the car ran a lot better but it still stumbles not as bad but still does. I am thinking i need to tune it because I ran out of options. And how can I tune it.? I also don't have an egr i have a plug for the connector and a plate on the intake and I don't have a smog system i plugged the back of the heads during the rebuild. I live in a state that doesn't check emissions once the car is 25+ yrs
 
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revhead347

Apparently my ex-husband made that mistake.
15 Year Member
Jun 14, 2004
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The distributors are known problem areas in these cars. Is the engine modified? Are you running an ignition box? What spark plugs are you using? What are they gapped to?

Kurt
 

gdushkin

New Member
Nov 6, 2019
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Check for codes, check fuel pressure and what is your timing set at?

I am running at 11 degrees and I am not pulling any codes because I just got the computer installed this morning but before that i had solenoid codes for smog but nothing else. And the fuel pressure is good since it is a brand new fuel system tank pump regulator injectors etc
 

gdushkin

New Member
Nov 6, 2019
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[/QUOTE]
The distributors are known problem areas in these cars. Is the engine modified? Are you running an ignition box? What spark plugs are you using? What are they gapped to?

Kurt
I have brand new cap and rotor the engine is barely modified as i stated above. I am also running bosh spark plugs they are gapped to stock specifications and a motorcraft coil the distributor is original.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
Flowmasters? Really? There is your problem!!!!!
No, seriously, we deal in real information, I like to see actual data, not 'I know it's got fuel pressure because it has a new fuel system'. Computer controlled cars need systematic diagnosis. Like what is your fuel pressure?
And I don't like bosch plugs but that is me.
Oh, and what does barely modified mean?
 

gdushkin

New Member
Nov 6, 2019
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Massachusets
Flowmasters? Really? There is your problem!!!!!
No, seriously, we deal in real information, I like to see actual data, not 'I know it's got fuel pressure because it has a new fuel system'. Computer controlled cars need systematic diagnosis. Like what is your fuel pressure?
And I don't like bosch plugs but that is me.
Oh, and what does barely modified mean?
Ok i just checked the fuel pressure is 38 psi while running. Barely modified is i have a bbk cold air intake and long tube headers that is pretty much it. I just checked timing it is at 10 degrees. And what is the deal with the flow masters ?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
18,481
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polk county florida
I'm just pushing your leg on the flowmasters, they are ok.
When you check the fuel pressure you need to pull off the vacuum line and plug it, the pressure should be around 42-44 lbs. Then put the vacuum line back on and it should be 32-34 lbs, then rev the engine up slowly beyond the trouble spot, this being over 3k and see it the pressure drops at any point, no drop in readings the fuel system is good and we need to look at something else.
 

gdushkin

New Member
Nov 6, 2019
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I'm just pushing your leg on the flowmasters, they are ok.
When you check the fuel pressure you need to pull off the vacuum line and plug it, the pressure should be around 42-44 lbs. Then put the vacuum line back on and it should be 32-34 lbs, then rev the engine up slowly beyond the trouble spot, this being over 3k and see it the pressure drops at any point, no drop in readings the fuel system is good and we need to look at something else.

Ok thanks I will look in to that tomorrow what vacuum line are you talking about ? the fuel pressure regulator ?
 

gdushkin

New Member
Nov 6, 2019
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Ok thanks I will look in to that tomorrow
I'm just pushing your leg on the flowmasters, they are ok.
When you check the fuel pressure you need to pull off the vacuum line and plug it, the pressure should be around 42-44 lbs. Then put the vacuum line back on and it should be 32-34 lbs, then rev the engine up slowly beyond the trouble spot, this being over 3k and see it the pressure drops at any point, no drop in readings the fuel system is good and we need to look at something else.
One more thing it usually doesn't do it when the car is not driving. On idle it can rev up to the redline it is only when it is under load like getting on to the highway flooring it is second or third and it starts to sputtering. But I will definitely re test the fuel pressure tomorrow
 

RichC93

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Jun 15, 2020
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So what did you figure out. My 93 does the same thing and I am about ready to pull what hair I have left out. 5.0, E cam, 70mm throttle body, 70maf 19lb, new 19lb injectors, cleaned lines, new pump, new distributor, plugs, wires, adjustable regulator 40lb, coil, tps ..... no codes besides the egr which is blocked off. I got the car as a basket case which I have been putting back together slowly but this stumble is driving me crazy. What's odd is as I rev the engine and watch the pressure gauge the pressure drops 5-8lbs....
 

gdushkin

New Member
Nov 6, 2019
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So what did you figure out. My 93 does the same thing and I am about ready to pull what hair I have left out. 5.0, E cam, 70mm throttle body, 70maf 19lb, new 19lb injectors, cleaned lines, new pump, new distributor, plugs, wires, adjustable regulator 40lb, coil, tps ..... no codes besides the egr which is blocked off. I got the car as a basket case which I have been putting back together slowly but this stumble is driving me crazy. What's odd is as I rev the engine and watch the pressure gauge the pressure drops 5-8lbs....
Well it looks like you have a different problem. But my problem was the distributor. Mine was still from the factory which my car is almost at 200k miles. I just bought a new distributor and it fixed it. Pressure of what drops? What kind of distributor do you have have you adjusted the timing ?
 

RichC93

New Member
Jun 15, 2020
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Codes.. Just the egr and canister codes.

155 fuel pump, tank was cleaned and is still clean. Also blew out the fuel lines and new filter.

Took the computer out and checked for bad caps also.

It's crazy because all the stuff is new... I have even tried the old ignition and downloaded the t/s guide from this website.

Runs and idles perfect but once you go to get on it, it starts to stumble and hesitate. The plugs are a nice shade of coffee color just off of white.

I just cant find the problem.
 

Foxslider

im not that much of a idiot
Oct 25, 2019
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It was the fuel pump on mine. My symptom was more severe though. Floor it and its just like fuel cut off completely. Over 3k also.

Which sucks if you have a new one and need to try another one cause they probably arent returnable. Just b/c its new doesnt mean its not faulty in someway. Call the company and tell them you have a new one you think might be faulty and see if they'll work with you.

Could be timing related as well. But i dont think it is by guess. I didnt use a timing light, i just go by feel. Ie: drive the car, pullover, adjust, you know when its better or worse and when ur in the sweet spot.
 

gdushkin

New Member
Nov 6, 2019
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It looks like a fuel problem definitely because of the color of the plugs. It is definitely leaning out. Do you still have the stock fuel pressure regulator. You can probably buy another one for under the $20. Do you still have your smog system. I saw on some other forums it could be a balancer if it is going bad it can throw off timing. How many miles do you have on it and if you can see if any rubber is coming off. It could also be a timing chain. That is really easy to check take the cap of the distributor and rotate the engine and see how much does it take before the distributor rotor moves if it Doesn’t move after a slight tug than you have to replace the timing chain. As for slider said it could honestly be your new pump Which one did you buy who is the manufacturer?