Ok guys heres the deal, 86 302V8 FI, starts up like a dream (plenty of fuel), drives great until you floor it or get on it. When you do and the RPM's get to the point where it should shift it chugs. Thought the fuel pumps were going but the fuel preshure regulator i put in is reading great preshure(37PSI) when it starts to chug.

The ENTIRE ignition system is brand spakin new!
Trans Flushed.
To many brand new parts to count.

This was the reason i rebuilt the enigne in the first place but its still doing it.

It's been to three shops two with dynos and no one can figure it out. Maybe one of you guys has had this problem. If so please drop a line.

Thanks Ryan

 

What RPM does it start to chug at? I gather you are at wide open throttle and before it shifts up it acts up.

 

is 37psi the right pressure? I'm sry, mines different since i'm supercharged.......but it still seems a bit low.

Check your spark plugs, you could be getting a missfire.

Your fuel injectors could be plugged. Dump in some strong injector cleaner, i know there is some good stuff out there...but i forgot the name of it, and see what that does.

 

When you say chug, does it hesitate and/or backfire?
Does it happen only with the motor under load or does it happen
when you rev the motor to the same RPM while sitting in nuetral?
Have you converted to mass air by chance? Ive had simmilar problems with my 90 mustang 5.0, had a dirty fuel filter one time and another time the mas air sensor was dirty, after doing a complete tuneup (which didnt help) I got a tip about cleaning the MAF and the difference was like night and day (but that might not apply to you if your not mass air).

 

Cat pluggin up?

 

That would be my guess as well. Get a vaccuum gage and take some readings.
Jes

 

I would also guess the cat as well.

 

Sounds kinda corny I know, but had a 87 Econoline 302 last week did the same thing.. I put a fuel filter outta desperation on it and it fixed it.. The thing was VERY heavy when I took it out..
Worth a shot!!


Good Luck


Keep us posted


FordMasterTech

 

rclay11541; Now I know this vehicel is not the same as my lincoln 4.6 32 valve but if you follow some of thes ford basic tips you will probally find some in this article, it was very helpful on a dtc code po 171 & po 174 that was driving me insane. Just use what you need to apply to the obd1 system that you have but alot of it can be applied both ways. I also had a stumble at high rpm's 6500 in my case that of course was WOT & in my case it was just the throttle bodie gasket & the fuel filter. Well here it goes FUEL SYSTEM MONITOR
Diagnostic Trouble Code Description Possible Causes
P0148 - Fuel Delivery Error At least one bank lean at wide open throttle. Fuel System:
· Severely restricted fuel filter
· Severely restricted fuel supply line

P0171 - System Too Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The code is set when the adaptive fuel tables reach a rich calibrated limit. Fuel System:
· Contaminated fuel injectors
· Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
· Vapor recovery system (VMV)
Induction System:
· MAF contamination
· Air leaks between the MAF and throttle body
· Vacuum leaks
· PCV system concern
· Improperly seated engine oil dipstick
EGR System:
· Leaking gasket
· Stuck EGR valve
· Leaking diaphragm or EVR
Base Engine:
· Exhaust leaks before or near the HO2S
· Secondary air concern
Powertrain Control System:
· PCM concern

P0174 - System Too Lean (Bank 2) Same as DTC P0171, but Bank 2. See Possible Causes for DTC P0171

F4.) Tips Related to the Fuel System Monitor
HO2S sensors are not likely to be the cause of adaptive DTCs P0171, P0172, P0174, P0175: Most warranty-returned HO2S sensors (replaced for these DTCs) are found to function normally. Additional related DTCs will normally be present if there is a concern with the HO2S sensors. Do not replace an HO2S sensor unless verified through pinpoint diagnostic tests found in the PC/ED Service Manual.
DTCs P0171, P0172, P0174, and P0175 are not related to downstream HO2S sensors: When diagnosing a vehicle with a MIL On and DTC(s) P0171, P0172, P0174, and/or P0175 in continuous memory, do not replace the downstream HO2S sensors. These DTCs have no connection to the downstream HO2S sensor function nor its diagnosis for faults. Always verify the vehicle concern, then perform the pinpoint diagnostics from the appropriate PC/ED Service Manual.
Diagnosing lean conditions and lean DTCs P0171, P0174: Freeze Frame Data can often help to identify the type of lean condition, even if the fault is intermittent, by indicating how the vehicle was being driven when the fault occurred. Diagnosis of lean conditions and lean adaptive DTCs can be difficult, especially if the concern is intermittent. Verifying the concern is extremely important. There are different types of lean conditions. The ability to identify the type of lean condition causing the concern can be crucial to a correct diagnosis. When DTCs P0171 and P0174 are both present, there is a strong likelihood of another concern being present:
Vacuum leaks/unmetered air: In this type of condition, the engine may actually run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is typically caused by air entering the engine through an abnormal source (opening), or due to a MAF malfunction. In this situation, the volume of air entering the engine is actually greater than what the MAF is indicating to the PCM. Vacuum leaks will normally be most apparent when high manifold vacuum is present, during idle or light throttle. If Freeze Frame Data indicates that the fault occurred at idle, a check for vacuum leaks/unmetered air when the engine is cold might be the best starting point.
Examples: Loose, leaking or disconnected vacuum lines, intake manifold gaskets or O-rings, throttle body gaskets, brake booster, air inlet tube, stuck/frozen/aftermarket PCV valve, unseated engine oil dipstick, MAF reading lower than normal, etc.

Insufficient fueling: In this type of condition, the engine may actually run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is typically caused by a fuel delivery system concern that restricts or limits the amount of fuel being delivered to the engine. This condition will normally be most apparent when the engine is under a heavy load, when a higher volume of fuel is required. If Freeze Frame Data indicates that the fault occurred under a heavy load, a check of the fuel delivery system (checking fuel pressure with engine under a load) might be the best starting point.
Examples: Low fuel pressure (fuel pump, fuel filter, fuel leaks, restricted fuel supply lines), fuel injector concerns, etc.

Exhaust system leaks: In this type of condition, the engine may actually be running near stoichiometry (14.7:1 air/fuel ratio), but the exhaust gas mixture will be lean. This condition is caused by oxygen-rich air entering the exhaust system through an external source. This condition will cause the exhaust gas mixture to be lean, even though the actual combustion in the engine may not be.
Examples: Exhaust system leaks upstream or near HO2S, malfunctioning Secondary Air Injection system.

MAF concerns: If a MAF concern is suspected, see TSB 98-23-10 .
Checking fuel pressure: Check fuel pressure with engine under a load when diagnosing a lean concern. A partially plugged fuel filter can be difficult to detect and can be easily overlooked if fuel pressure is only checked at idle. The same is true for other types of fuel supply concerns (e.g., bent or kinked lines, degraded fuel pump).
At idle, an engine requires only a small volume of fuel. Due to the fact that there is a small volume of fuel needed at idle, a restriction in the fuel supply line in many cases will not cause the fuel pressure to be low. When the vehicle is under a load, the engine requires much more fuel than at idle. Under a load, a restriction in the fuel supply line will prevent the high rate of fuel flow that is needed to maintain the correct fuel pressure.