b4wheeler

iTrader: (1)

Little back story....

Driving today and all was fine. Ran as great as always.
Came to a stop light and when going again, the truck would not accelerate. Sorta fell flat and stumbled and would not go...

If I shifted to a lower gear and revved the engine to get the rpms up, and let the clutch out , I could go better. Not great but better.

I had a spare AFM and swapped it. No change.

Checked all plug wires at cap and coil. All good.

Got home, Finally and changed plugs, cap and rotor......

All the old plugs looked fine, no oil or coolant on them. No oil milkshake....

I have done all the searching and just need to know if someone has an idea.....

This is not a specific cylinder problem, but feels like a general ignition problem.....

If I hold the accelerator down, the engine will clear up and run fine, until I try to put it in gear and go.. Seems like it will run free but not under load....

All ideas will be accepted.

scope103

Ignition timing is set to ...?

b4wheeler

iTrader: (1)

Factory.. according to manual.. Not sure really... !2-15*

That hasn't changed....Unless a cam jumped time all of a sudden... But it will "clear" up and run fine if I keep the accelerator at a constant position.. Usually right around 4K is where it stay clean and runs fine .

courtgordon

well youve already addressed fire so sounds like fuel issue

b4wheeler

iTrader: (1)

I think I am going to do the fuel filter next... Not sure it has ever been done....

Truck will idle just fine... Just wont run when put in gear and trying to drive....

crazytexan

iTrader: (1)

I had something similar to this, But With an Auto all i could do was coast off the road, shut off, and start up again in a minute or two. It held idle, but could not rev past 1500. After doing tests the Fuel pump WAS good, But rail pressure would not hold after engine stop. Someone told me the check valve in the fuel pump was bad. All I can say is i put a gauge on the rail, And changed the pump from a donor parts truck, had not had the problem come back again.

scope103

Sorry, I'm not following this. Do you mean that you DID check the timing, and even though you don't know now what "factory" timing is, that is what the timing was? Or do you mean that so far as you know no one has changed the timing since the truck left the factory, and you don't believe the timing could change without you doing it?

Valve timing and ignition timing are not the same thing. Ignition timing can be off due to simple wear in the distributor, and it can slowly get worse. It doesn't require a "cam jump."

This may not be your problem (though the symptoms do match), but checking timing is a whole lot easier than trying to measure fuel pressure.

b4wheeler

iTrader: (1)

What I was trying to say is, I put his engine in last spring and when I did that, I installed all new service parts (timing belt, water pump, oil pump, rear main seal, rebuilt injectors.....)
Any part that could be replaced while out of the vehicle has been replaced.

At that time, the valve timing was set and ignition timing was set to factory specs according to the factory service manual.....

I am not sure what the factory ignition timing is, but I believe it to be set to 15* BTC

Sturmcrow

My odds are on fuel filter or pump. Your symptoms are exactly the same as the couple of times that I let the fuel filter go too long without changing.

b4wheeler

iTrader: (1)

Fixed with new fuel filter...

New issue... ->
Truck ran awesome before the filter problem. Now it seems to be sluggish, and have a kind of flat spot in the rpm range... It still runs well, idles fine... just does not pull the same. Need to run in fourth gear more often and cannot accelerate just buy hitting the gas... Need to down shift a lot more.....

Only difference from before the filter problem is a new cap, rotor and plugs.....
I installed a set of NGK platinum plugs.. Original set were NGK coppers... Thinking of going back to coppers, because it always ran great with them....

RBX

You never mentioned if you have checked for any codes, unless i missed that.
I had a bad spark plug after putting the new heads on, and it ran terribly. I couldn't figure it out, I took a timing light to each plug line to make sure they were getting spark(they were new before I tore the top end down).
Could be an O2 wire issue. As I understand our engines only really sniff at low RPMs, which would explain why you get decent performance when revved up.

Hope that helps, not sure what you are experiencing exactly(not there).

b4wheeler

iTrader: (1)

I have had codes for a while and it never effected the way it ran...

I have o2, knock and egr codes.....

I have a new o2 for it, but havent had time. KNock will not get done because I dont want to go into it.. Dont know why I get EGR, I have replaced the entire system and no change....

All these codes existed before I had the fuel filter problem and it ran fine, so I have to conclude that they are not a problem now......

Only difference is the cap rotor and plugs.....

So thinking of changing the plugs back to copper and get rid of the platinums....

scope103

I can't explain why your truck ran "fine" before replacing the fuel filter, but the knock sensor code is supposed to be coupled with severely retarded computed timing. Which would make the truck run like crap (or at least make it seem like it lost a lot of power).

If your "O2" code is for the heater, that would only have an effect near startup or at low rpms, so it would not be a too noticeable effect. Your EGR code would mean you are putting out a lot of NOx, but would probably not have a big impact on performance.

Good luck trying to get the power back by changing the plugs.

RBX

If you have some known good plugs laying around, I'd swap them in first to see if its the plugs.

I have my EGR removed, and NONE of the emissions crap hooked up except the evap and O2, and I have no codes, ever. My rig is an 88 also, maybe you have an EGR vac line leak? Maybe you have a California emissions model? I do not, but I understand the Cali models have finicky ECUs.
The knock sensor will make the truck run terribly, I had that when I first go the the truck. That was one of the first things I fixed. Yes, it is a PITA, but I understand it is an unavoidable issue that will need attention. How you have been getting away with it contradicts everything I've ever read, and experienced. Not saying it can't happen, just saying.
Wait, you said you just rebuilt this engine 2 years ago? Did you fix the knock sensor then? I'm guessing you did. So did it go bad in 2 years? The pig tail can easily get messed up during reassembly.
I'd get the O2 on there, clear the codes, drive it, check again.

I wouldn't want to get into the knock sensor either.

b4wheeler

iTrader: (1)

RBX..

I put a newer engine in a couple years ago, while I was there, I replaced everything on the engine that I could... New front end(water pump, oil pump... blah blah blah....)
Knock sensor is in and rewired, but getting a 51 or 52 code... Never had a problem with the way it ran, maybe it will run even better...
21 O2 code... Don't know why, same o2 as old engine.......
EGR code... WHY??? same egr as old engine... replaced entire EGR system and still get code....
PAIR system removed. Headers. No Cat.

All not a problem. Never had a performance problem before the fuel filter problem..

Replaced fuel filter, now runs different....
Has flat spots, but can down shift and run it at about 3000rpm's and it is fine.
Previously could run in 5th gear and just accelerate up hills. Now I need to downshift and run 4th and find myself leaving it there often.....

If I still had the old plugs, they would go in..... Maybe I need another fuel filter... (bad filter)

[Also..... riddle me this..... also have a drive-line load/unload issue when getting on or off accelerator..... Don't know when this started.. Totally unrelated, i know, just wanted to throw out there... Hoping rear is not going... .Don't have new housing for e-locker yet]

RBX

Load unload driveline sounds like slip joint needs grease or is worn. When it doesn't have grease it feels like the spare tire wasn't cranked back up tight, kinda clunkish feeling.

I guess a bad fuel filter is possible, you did install it properly (in - out) I'm assuming.

I'm home from work today, if you like, I could swing down and take a look at it. Not guaranteeing anything, but sometimes it helps for another set of eyes.

b4wheeler

iTrader: (1)

FIXED!!!

Turns out it was the connection at the TPS.

I had read something online about a Mazda running poorly and when they disconnected the TPS it ran better.....

Well I checked that and found the little spring that holds the connector on the TPS was missing. So my TPS has been disconnected for a week now and it is running a lot better.
Still need to get it connected properly to make it run the way it should, but for now I can drive it and just have a little laziness below 2000rpm....

RBX

Glad to hear you fixed it, sorta.