Hesitation thread #3,302,183. Searched and have come up with nothing
 

Hello again,

My car seems to have a really odd hesitation. When I first start up the car and begin to drive it, it doesn't really hesitate at all, but after it warms up, it starts to hesitate real bad, like it has no power and won't accelerate. An odd observation, and maybe negligible, but the oil pressure gauge works sometimes when the car is cold and then stops after the car warms up...around the same time when the car begins to act funny. Odd, huh?

This is what the hesitation is like when I'm driving: In first gear from a dead stop, I have to ride the clutch to about ~2k rpms just so it won't buck extremely bad and make me look like an idiot. I have to also shift at 3k+ so it won't buck and allow me some power to accelerate in the next gear, because if the rpms are too low, the car will just buck like crazy and not go anywhere. I also seem to notice when I begin to give it a big more gas, you can hear and feel the bucking a lot more. It sounds like it's going "put put put put" really fast.

Also, every time I go uphill, the car will just slow down big time, and when I try to give it a bit more gas, it won't go anywhere and just give me an odd "pop" sound. I don't give it a lot of gas so it won't boost, but when I begin to feel it transition, I just back off and go slow as hell up the hill. Oh, and during the entire time I'm going uphill, the temp gauge begins to creep higher and higher.

What i've tried so far:
Pulling engine codes- My check engine light isn't on, but I still tried doing the TEN and GND and no codes come up.
Unplugging the o2- Nothing.
Adding extra grounds- Intake manifold- Body, Starter body- Battery ground, Alternator body- Battery ground, Battery ground- body, Alternator positive- Battery positive, Starter positive- Battery positive.
Setting the TPS- TPS is perfect. Car idles 100% perfectly.
Checked if cat is clogged- Nope.

I guess I could check the fuel pump relay to see if it goes on high, but the problem exists below 2k rpms as well, so that would rule that out.

Engine is freshly rebuilt, rebuilt injectors, new fpd, silicone vac lines, new plugs, wires, oil/filter, etc

Mods: Downpipe :)

Thanks.

-Andrew

Alright, I'll offer $20 bucks to whoever can figure out my problem :p: So start throwing out ideas. :D

new fuel filter?

Here are a couple of ideas. Some of these are common sense, but I'd rather cover all the bases...


-Check ignition coils (test resistance when warm)
-Replace engine thermosensor
-Check "crankshaft sensor" wiring, be sure sensor is securely mounted (sorry I don't remember what this sensor is called on a rotary)
-Swap in another ECU
-Check for vacuum leaks (use carb cleaner)





Good Luck,
-s-

I suggest you check fuel pressure. If that's ok, then take it to someone with a wideband O2 sensor. Then figure out if you have a fuel problem.

Bad injectors can cause the problems you have and be hard to detect without a wideband. Even if they are/were just cleaned or rebuilt.

Dave

Well it obviously sounds oil related...what kind of oil are you using? Have you noticed any leaks? Are your coolers working? Do you know the oil temp? Seems liek you definitely have a loss of pressure? Whats your vacuum read when you warm up?

It sounds as though he is loosing all oil pressure in the car when it warms up...Thoguh this does somewhat fuel related as well, but I think the real problem her eis his oil pressure...have you checked your oil level? Are you loosing coolant? THoguh the ECU wouldnt surprise me at all....who rebuilt it? What are your MODs?

If you don't have any bucking under full acceleration then buy a PFC and you'll be fine. This sounds like a case of standard electrical issues with the FD and stock ECU. When driving at low RPMs on a flat road in 4th gear do you feel a slight pulse in acceleration? If so just buy a PFC and you'll loose everything but the pulse and I bet if you replaced the engine harness and battery side harness this would go away as well.

However if it bucks when you floor it then I'm betting it's your injectors, fuel pump or something electrical related to fuel.

A messed up ECU would cause the oil pressure gauge to just stop working when it warms up?

seems like the exact problem i had.. turned out to be shit in my fuel tank clogging up the fuel filter. id definately change that and remove the fuel pump and check inside.

Oh I see what your saying. When the engine is cold it pumps extra hard fuel wise to compinsate for cold start so hes able to drive it kind smoothly becasue the ecu is loading extra fuel thuse allowing the fuel. When ti warms up it back off on the fuel. thus a drop in oil pressure becasue its not loading as much. I get it. Its not that it stops workin its that it isnt using as much oil pressure due to poor combustion and fuel amounts?

The oil pressure IMHO is a red herring - the factory sensors typically read lower after they heat up once they get some miles on them. The OEM oil pressure senders just aren't that good - mine lasted 20-25K miles before it started reading low.

Once things get warmed up, the heat in the sender alters the resistance making it read low.

I'm also all for checking fuel pressure on this problem - with intermittent problems like this, you need a clean slate on the maintenance items - plugs, wires, fuel filter.

Dale

I am assuming the fuel filter is still original, so it has ~57k miles on it. I will look through the receipts to see if it was recently changed though.

Ignition coils- Will do. Can the harness going to the ignition coils be a problem too? Reason being is the plug going to the battery harness to the plug from the ignition harness melted (don’t ask :p: ) So I had to cut both ends of the plug off, get another plug, and match the wires back up. I matched them all right according to the fsm, but I just wanted to throw that out.
Engine thermosensor- Coolant sender? Sorry, I’m not sure what you mean.
CAS sensor plugs/wiring- Secure.
ECU- I bought a good condition ecu because my original one was bad. The previous owner had no problems with it, so I should be able to rule that out.
Vac leaks- None.

Fuel pressure was fine when I was testing for leaks a few weeks ago. Can my a/f really be off that bad on a stock car?

Castrol GTX 20w50. No leaks. Not sure if coolers are working and not sure on temp. I think it might be a sender problem, even though it’s the second one I’ve tried. Vacuum is ~16 in-hg.

Just changed the oil yesterday, oil level is fine. Coolant level is fine. Rebuilt by myself and Tony Lucky 7 Racing. Only mods are a downpipe.

I really don’t want to modify the car at all. I want it to be as close to stock as possible. So I really don’t want a PFC. I’ll try the 4th gear thing tomorrow. I haven’t gone full throttle yet because it’s a rebuild. Engine harness and battery side harness were replaced.

I think it might be a loose connection at my gauge cluster, or I need to clean the connection to the sender.


I’m starting to think it might be the fuel filter clogging up. I got the car with a pd fire and it might have sucked some crap through the fuel lines, because when I opened the block there was a bunch of small crap (plastic and rubber) inside. Or the fuel pump sock.


Mdpalmer hooked it up with a good oil pressure sender because I thought mine was originally bad, but I still get the weird gauge reading- It won’t go up in pressure smoothly, but just straight to a certain amount. It’s weird…
I checked the fuel pressure a few weeks ago and it was fine, so I don’t think it is that, but I guess I could check again. I do have new plugs and wires though. I just need a new fuel filter now.

Looks like my incentive program works :p:

Change the fuel filter. Pull the fuel pump and make sure that's clean too. If there is any doubt about these do them first.

Then if the problem continues, consider the injectors. Injectors can stick open or stick shut, causing hesitations and misfires.

Dave

andrewdruiz,

Have you removed or messed with your double throttle?

I have the PFC and the pulse in acceleration when i'm not at WOT. It drives me nuts- not as bad as the OEM ECU hesitation though.

Who did the injectors? Wasn't RC was it?

Sounds like maybe your Engine Coolant Temperature Sensor has gone open, or the connector has become disconnected. Are you getting black smoke? Tap into the voltage with a voltmeter probe between your ECU terminal 3E (green wire with white stripe, middle connector, 3rd wire in from one end) and chassis ground. When cold, it should read about 2.3 volts; when hot, about 0.4 volts. If it is stuck at a high voltage (like 5 volts) or if it does not drop down as the coolant heats up, the problem is there.

These cars have three devices that are reacting to a change in coolant temperature.


I'd check the 2-wire sensor in the thermostat housing that the ECU connects to: just measure across the terminals and make sure you don't have any crazy voltage spikes, and be sure it's actually changing when the temp changes. I'm pretty sure this sensor is called the thermosensor in the Mazda service manuals, but I don't have an FSM handy to double-check this.


The other two "coolant sensors" are the sensor in the rear iron (which is only used by the temp gauge on the dash), and the 1-wire thermoswitch which is also in the thermostat housing (the thermoswitch switches the fans to a higher speed at a certain temperature).

To check ignition coils, search for "ignition coils" and my username; I created a thread asking for help a couple of years ago, and people posted some very helpful info.

-s-

I checked the fuel pump today and the sock and tank seem to be pretty clean, so I can rule that out. I still haven't gotten a new fuel filter yet, but I'll try to get one today. Here are a few pictures.

Nope. Should I?

Witchhunter did them. I have the before/after flow sheets and everything looks good.

No black smoke. I'll check the connector and voltage later today.

The 2 wire sensor you speak of, is this the same one in the post above yours except a different way of measuring it?

The 1 wire sensor on the t-stat housing might not be working, because my fans don't go on at all. I have to turn the a/c on and even then only one works and it's on "low" speed. They worked fine before I started driving it, but for some reason they stopped working normally. I'm guessing the sensor in the rear iron is negligible because it's only for the gauge.

Alright, well here is my current "to-do" list:

Change Fuel filter
Test Ignition coils
Test Engine coolant temp sensor

Thanks.

Yes, wstrohm and I are talking about the same sensor; if you're not able to get to the back of the ECU, you might be able to measure the back side of the connector in the engine bay. Be sure you're measuring things while the sensor is plugged in.

If the ECU doesn't know the correct engine temperature, weird stuff will happen.


-s-

Alright fellas,


I tested the 3E connector at the ECU. This is what I got:

Cold- 3v (FSM specs- 2.5 volts) FAIL?

Warmed up- .3v (FSM specs- .5 or below) PASS


Next I tested the resistance between the two wires on the thermosensor. This is where it got WEIRD...

I first started by unplugging the plug on the back of the wp housing for the thermo sensor and just for "fun" I put my multi meter on the plug (coming from the ecu) and guess what happened? The right e-fan turns on low (my left one stopped working for some odd reason) and the two lower relays (that sit right next to the passenger's side shock tower where there are a total of 4 relays- 2 top and 2 bottom in rubber protectors on a mount) clicked. So I kept messing around with my multi meter and the e-fan kept turning on and off as well as the relays clicking on and off. The measurements were all over the place, so I won't bother giving them. Isn't that weird? What does this mean? Is it shorting somewhere? What are those relays for? :confused:

Next...

I started blipping the throttle slightly to see what it would do when I'd give it more gas, and when I began to give it ~50%-75% throttle off-idle, the engine would either: 1. Shake for a second then die 2. Shake, rev up to a few thousand rpm, then come down and die 3. Shake, rev up, and not die. Could this be fuel filter related?

And finally I tested the coil packs and this is what I got (measured in ohms):

Leading- A-B connection ~.9 (FSM Spec- Below 1) PASS
-L1-L2 connection- ??? Unable to get reading. My multi meter isn't long enough to touch the ends or something like that. How did you guys measure it?

Trailing 1 and 2- A-B connection~1.1 ohms (FSM Spec- Below 1) FAIL
-A-T connection for both T1 and T2- ??? Same result as L1-L2 connection

No local places had FD fuel filters, so I have to order it from Ray. I think the problem might lie with that "short" at the coolant thermosensor.

Andrew,
Any luck with this problem yet?

I'm still leaning toward fuel if it's pronounced and ECU if it's mild.

Keep us posted if and when you figure it out.

Thanks,
Fritz

i would think it's the fuel pump's problem...
i previously had this issue when i switch ECU.... my car has a seperate fuel pump relay... the grounding of it wasn't hooked up...

the car idles well.. but never able to put more gas... once more gas is given.. the car hesitates like crazy....

try looking for some connection inside the bunch of ECU wires for any breakage.. or the ECU's grounding point isn't good enough.

It was the trailing pack.