Hesistation/load up under light throttle, can't figure it out!
 

I bought my 87 turboII at the end of november off of a member on this site, it had a hesitation or load up under light throttle at 3k rpm's and under. After 3k rpm under light throttle it runs how it should, and mid-wot it runs how it should as well.

I tested everything on the car, did a tune up, tested everything I could with my DMM and I couldnt find anything wrong besides the tps wouldn't read past 2k ohms.

So I had it towed to JPR Imports Dec 2nd. He sent out the injectors to get cleaned, thought they could of been it but they were not the problem. He tested out another ECU and that wasn't it either. Jim said after that he checked all of the wires on the wiring harness and they are all fine.

He said he doesn't know what it is but it's not electrical, so he's going to do a compression test, he thinks maybe a seal is stuck.

I only got to drive this car for one day, the motor pulled very strong and pulled good vacuum as well and only had that problem under light throttle so I figured the motor was perfectly fine and it had to be something electrical.

What do you guys think?

The TPS not going beyond 2k ohms is an issue that should be addressed and could very likely have a lot to do with it. With the TPS not going over 2k ohms the car would likely get stuck in closed-loop under moderate throttle.

From what Ive read the slightest problem with your TPS can cause these problems.

He replaced the TPS from what I understand cause I made sure he knew about that before he started working on it.

It only exhibits this problem under 3k, but could it possibly be a ground cause I remember seeing the ground on the engine looked a little rusted, or could it be the wiring at the fuel pump?

I just don't understand how it could be the motor, it idles even, no smoke, pulls extremely hard under wot and pulls good vacuum

I'd check the TPS and it's sweep range to make sure it's within spec (just for giggles). Grounds can sometimes be an issue as the secondaries come online, but that's usually not right at 3k rpm.

Just to add to the theories...I wouldnt think it is fuel pump wiring because you would really know if it was messed up there. Id definitely check all the grounds because that would be good for the car in general.

As for the TPS again, he says he replaced it, but Ive heard they are fairly hard to acquire. Maybe he told u he replaced it but didnt. If it isnt reading as it should then fix it

The car is still at the shop otherwise I would be able to check the tps and clean the grounds.

I just talked to him 2 hours ago and thats when he said I tried another ecu and checked the wiring harness and everything is fine then said he thinks it could be something in the motor like a stuck seal.

Its been in his hands since dec 2nd. It idled even, 0 smoke out of the exhaust, good vacuum, and pulled hard under wot, so I don't get how it could be the motor.

I figured it would of been a simple fix and would of had it back by now since its currently suppose to be my daily driver.

I just don't know what i'd do if he says its the motor even though I don't see how it could possibly be the motor since the only problem the car showed was a hesitation or load up on light throttle under 3k rpm.

I made a post on here before I put it into the shop, told you guys id update you guys on what was wrong after it got fixed.

I am just trying to think of anything that could be causing this besides the tps, ecu, injectors and the ecu wiring since he said he either checked all of those or replaced them.

Id have to agree with you, sounds like a logical pattern of thought...But that doesn't address the fact that your TPS only read less than 2k ohms. Is that WOT or idle or what?? From what Ive learned its supposed to be up at 4k to 6k @ wot.

before I put it in the shop I set it to 1k at idle while opening the throttle it went up to 2k ohms which was almost at wot then at wot I would get no reading from the DMM

It should move from ~1k ohms to ~5k ohms, if it goes open (or to infinity) on your MM it's a short in the TPS and will cause all kinds of silly hesitations and trouble. Have you driven the car since the new TPS was installed? I'd figure a new TPS (that tests fine, at both the TPS and the ECU) would've resolved the issue after saying that. Also, the S4 TPS is narrow range, it typically reads from 1k ohms at idle to a max of about 5.2k ohms at around 35% throttle, afterwards from then on to WOT it just reads it's highest value. It shouldn't be linear all the way to WOT, it should max out pretty early.

When you tried to check your tps was it disconnected?

No I havent driven it since he said he put in a new tps, the car is still in the shop, I havent went to the shop at all yet since I had it towed there.

I checked it when it was connected and disconnected after I had the car warmed up. JPR said it was faulty and said he replaced it.

I think at this point, if your TPS really was faulty originally it was very likely the cause of your problem. I'd have the new TPS tested to verify it sweeps from 1k-5k (or around there) from closed throttle to about 30-40% throttle. If it takes full throttle for it to sweep, or it's not sweeping there's possibly something wrong with the linkage that's attatched to the throttle plates. Have them check the TPS operation, if it checks out my guess is your problem would be resolved.

Ok so your saying when I go to get the car check the tps. It should sweep from idle (1k ohm) to 30-40% throttle(5k ohm), if it takes wot to get to 5k ohm or if it doesnt go to there then I should look at the linkage connecting to my throttle plates and see if its damaged correct?

In short, yes. Or even ask your mechanic to verify that the cars having problems with the new TPS installed. I would think that given what you said previously about your old TPS, this would've solved the problem completely. An engine issue would result in idle/power issues, usually not have much to do with light throttle at all. I usually find it's either because the vehicle sticks in closed-loop too long, or there are 'blow-opens' in the TPS sweep.

If you check the TPS and the new one is having issues (either only reads to 2k at 30-40%, or takes all the way to WOT for it to sweep up to that value), look at the TPS plunger itself, you'll see it rides on a metal cam which slides against the plunger and pushes it in as the throttle closes. If that metal cam is in contact with the plunger throughout the entire range, it's either been damaged, or tampered with.

I've seen people intentionally modify it to do this for use with aftermarket ECU's or even SAFC's so that they have full throttle feedback, but on a stock ECU it'll introduce trouble.

I will call tomorrow and ask, I remember when I was checking the tps and the cam that rests on the plunger would move way further then the plunger at wot.

The plates being out of spec does seem like that may be it because the engine might be getting more air then its thinking causing the hesitation on light throttle under 3k rpm.

I have a quick question, if I bought a rtek 2.1 ecu installed it and tune the fuel and timing tables wouldn't that be a way to rid of this hesitation since the maps are based off of load and the tables are programmed into the ecu? It would know how much fuel and timing to deliver at each rpm point so I would imagine that would resolve this issue that can't be figured out.

I decided not to call today cause I really don't want to bother him since he said he replaced the tps, cleaned the injectors, tried another ecu, and checked all of the wiring on the harness.

I just thought that this would of been a simple fix like replacing the tps since it seemed like something minor due to the hesitation only occurs under 3k rpm only under light throttle.

Never did I think that I would be without a vehicle for over 6 weeks and there would be something wrong with engine.

I'm just hoping my luck will turn around soon and not have to deal with so much stress.

Have the guy check the injector clips to the Injectors.Primary injectors.(for the hell of it.)
I had a slight Misfire/bog on my car and it was a bad connection at the injector.It was just "on there" but not totally connected,when the engine starts 'vibrating' due to Revving it would shake the primary injector clip and create that scenario.

When he calls me I will ask, I would imagine that he tested them with a DMM since he said he checked all of the wiring and said if the ecu swap doesnt benefit at all then he would check the injector wiring to see if its bad at any point in the wiring.

I talked to him this past wensday, he said the car is all apart and since he has so much time into it he said he has to fix it. He asked if I had a wiring harness for it which I don't so I said no, so I guess hes going to try another harness and see what happens. I am hoping this will be finished soon.

Ok JPR imports called me yesterday, he said he replaced everything around the motor like the coils injectors etc and said the car still showed the hesistation/load up under light throttle below 3k rpm.

He said hes tried everything and it must be the wiring harness cause thats the only thing he hasnt swapped out for a different one, so he wants me to find a harness and get it to him so this thing can be fixed i hope.

He even tracked down the original owner of the car, said the original owner said when he dropped in the new engine it showed the problem and he couldnt figure it out and thats why he sold it, and im guessing thats why the forum member on here sold it to me.

I really would of never thought that this car would be in the shop for over 2 months, figured it would be a easy fix for JPR and I couldnt figure it out. Figured he would of had it fixed within a week but instead seems like it turned into a nightmare.

Damn this really sucks, I feel like im screwed and def got screwed. Getting this thing to run correctly on a stock ecu/wiring harness correctly isn't going to happen :(

Well, lets start from the very begining again. Can you better describe exactly what's happening? For example, if you're at a stop sign/light, cars idling at 750rpm, you rev to about 2k, ease the clutch out and roll forward @ about 20-30% throttle or so, does it kind of hesitate/buck/surge around 3k rpm? Describe exactly what it's doing and I'll toss some more idea's out. I'm afraid to know what this is going to cost you, especially since they kind of went at it from the 'lets just randomly replace everything' approach.

Also, it's going to be a real pain to help when you don't have the car in your posession. Like it'd be useful to know if the car goes lean/rich at this area, and it'd go a long way to having a passanger with a DMM to do some tests while you're driving around reproducing the issue.

at light throttle trying to accelerate it would act like it is really loaded up bucking yea in 1st gear it bucks real bad.

I know I dont want to see this bill, he said only thing he can think of is that there might be a break somewhere in the harness.

BUCK makes me think LEAN.

Stepping on the pedal and the car bogging sounds like too rich. Like stepping into a bowl of mush.

A messed with afm can cause your problem. That can not be determined with any FSM check outs.

Screw the B.S with resistance of the TPS. Go to the ECU and read the TPS output with a fully hot engine. The reading should be approx one volt dc. Then slowly step on the pedal and the voltage should slowly rise to 4.5 to 5vdc once the throttle pedal has moved far enough to start opening the secondary throttle plates. From then on it should remain at 4.5 to 5vdc til you hit wot.

Your problem with reading the resistance of the TPS sounds more like an operator problem than anything else to me. Like the meter isn't set on the right scale.

Go to the FUEL AND EMISSIONS section of the FSM. Go the section called CONTROL UNIT. Then backprobe each pin of the ECU plugs with a digital meter and compare the results to the readings on the CONTROL UNIT page.

YOu might even try just disconnecting the TPS's connector and go for a ride to see if the problem has changes or not.

BUCK sounds like LEAN to me. Got the right fuel injectors in the primarys? Look at the numbers on the injectors to see if they're the right ones or not.

When I got the car, the first thing I did was check the numbers on the injectors. The primarys are the factory 550cc injectors and the secondaries are the 1st gen secondary 680's.

I did disconnect the tps plug to see if that would change how it would run, disconnecting the tps didn't change how the car ran it still produced the same exact problem.

Jim wants me to get him a ecu wiring harness cause he thinks mine has a break in it somewhere, and he said he tried replacing everything around the motor to see if the coils, injectors, ecu, afm, etc. were faulty but the car still produced the hesitation so he believes its the harness since thats the only thing he hasnt swapped out for another.

I got tired of waiting on this to get fixed so I called a few weeks ago to see if I could just take it out of the shop since I need something to drive and I would of just dealt with the hesitation but he said he has so much time into the car that he has to fix it.

The forum member that I bought the car off of on here sells second gen parts, I asked him if he had a harness on hand and he said he didn't so I got to wait till a harness in good condition pops up. I thought Jim at JPR Imports would have a spare but I guess he doesn't so I got to wait to get one, then hope the harness thats in the car does have a break in it and the new one will fix it. Then I will be able to work again finally.

Thank you for the advice HAILERS, I really appreciate it!

Are you running anything along with the original ECU to modify flow for the secondaries? Did someone wire in resistors for the secondaries or do you have an original resistor pack installed? I'd be weary of leaving it at a shop any longer because like I said before, it seems like a random replace whatever approach that I can only imagine is going to cost you an unimaginable amount in the end. Is the RPM exactly at 3k? Have you verified with a more accurate gauge that this is where the hesitation is? Has someone checked the ohm reading on the 4 injectors vs the ohm reading @ the ECU?

This will sound stupid, but try disconnecting your O2 sensor or o2 sim wire if you're running a wideband. I had the exact same problem as you, but only after i installed my wideband. Unplugged the o2 sensor and it was gone. Mine was getting confused and kept cutting fuel sporadically. I have an o2 sensor DTC all the time but the car runs fine

also you should check for vacuum leaks, like the TID where it meets the turbo compressor housing inlet for a crack. Also, make sure the injectors have the correct clips on them, look in the FSM to verify that you have the primaries and secondaries connected to the right wires. Mine has been having a problem almost exactly like that and I haven't put my car back together yet, but I did find I had the primary injector clips on one primary injector and one secondary injector, and vice versa for the secondary clips. Also, one more thing I plan to look into if that doesn't solve my problem is my lack of a 'restrictor pill' in the vacuum line that runs to the boost sensor. GL.

Totally stock ecu, no resistors for the secondaries that I have seen. I tried taking it out but he said he has so much time into it that he has to fix it. It will produce the problem at or below 3k rpm. He said he checked everything at the ecu then at the other end of the wires and its all within spec.

Previous owner removed the o2 sensor wire/plug and there is no bung in the downpipe... Its a custom made downpipe. So I have no o2 sensor in the car.

JPR did a vac leak test and he fixed the leaks that he found. If the clips were not on correctly I am sure he would of corrected it, I dont believe I have a pill in my boost sensor line as well.

I'd check to see if you have an OEM resistor pack installed (it's underneath the AFM, bolted on the front portion of the inner fender). If you don't see anything there, check resistance of the injectors @ the ECU. If you're running low/high it's could cause some issues. Infact, I'd probably remove the 680's entirely for now until you have some method of adjusting them, that itself can be causing all kinds of issues. Is this a 100% stock ECU?

Ok... I just found a picture of your engine bay. I can see you don't have a stock injector resistor so you NEED to check the resistance @ the ECU to see if someone installed them inline. It's possible to damage the injector drivers firing them without. Next, move you pressure sensor's location off of that silly plastic line that goes behind the manifold and connect it to either the nipple @ the ACV (if still installed) or to the nipple coming off the UIM (somethings connected to it already but I can't tell what it is or where it goes, i think it might be the long hose that goes to the BOV). Next, you've got a S5 engine and some s5 externals. Is the intake/TB s5? Is it using a S4 TPS attatched to a s5 bracket or is it a normal s4 tps? Have you verified that the TPS range goes from 1v @ idle to ~4.5-5v at 35-40% throttle like it's supposed to? I know it has S4 TII primaries. Also, check to see if the restrictor pill still exists in the boost sensors line (you should feel it where the white dot is painted). I also don't see a sticker on the pressure sensor, are you sure it's a TII sensor?

Does the stock injector resistor effect the primary injectors? ACV was removed by prev. owner. I asked JPR if the TPS swept through its proper range and he said it did. If I had the car in my possession I would take more pics so you can have a better look at things.

If the stock injector resistor effects the primarys then this might very well be the problem.

100% stock ecu yes

I'm not sure if it can screw up the primary injectors circuit or not, I've never really examined how the internals work. I'd try to move your boost sensor if you can (and verify it's the proper one, I couldnt see the model #). I'm unsure if it's using a S5 TB with a S4 TPS attatched to it, or if it's a S4 TPS. They could've put the S4 TPS on the full throttle sweep, which could cause some issues. It should go full at ~35-40%. Also, have them locate/check the resistance value of the O2 sensor wiring (making sure it's not touching anything giving false reading back to the ECU). Depending upon what RPM you're reaching, it could be the secondaries being too large (and uncorrected) having something to do with it, but that usually happens later in the RPM range so I don't think that's it. Have they made sure the right injectors are connected to the right plugs? I've seen some people hook up the primaries to the secondaries before... Given that it's kind of a mix/match engine with some unusual things it's hard to come up with ideas to suggest without having something to look at/results.

Test the injectors, make sure they're all 12+ ohms @ the ECU (I'm guessing the secondaries won't be which would be bad), install an O2 sensor & wire so you can monitor the O2 value when it does this (even if it is just the horrible narrowband for now). Check TPS sweep voltage to make sure it's not doing a full sweep, then backprobe all of the ECU values and look for things out of the ordinary.

If they've tried another AFM/ECU/Pressure sensor it would eliminate having to check that stuff. Also verify your thermosensor values are showing up properly @ the ECU.

Thank you for your input, I was told its a S5 engine. I don't know how to check if the manifolds are s5 or not, same with the throttle body. I would hope the tps is a s4 and not a s5 since its running on a s4 ecu.

If I could find a s4 t2 harness for sale and get it shipped to jpr I would be happy cause then we can figure out if the harness is the culprit or not.

I will update you guys when I get more answers, I can't really give out much more info since the car is a hour away from me and I think all the possible causes and troubleshooting ideas have been stated.

Just need a ecu harness and go from there. I really hope thats the cause, I would be so happy to finally be able to drive a 7 again and be able to get a job and work. This whole thing and other crap in my life has me super stressed and depressed and I would like things to turn around for the better

Well, the problem with that is you're going to end up dumping money on a harness that really isn't all that difficult to check in place. There's not a whole lot of sense behind replacing the engine harness on a whim to see if it takes care of the problem. The manifolds won't really matter much, nor the TB, it's just how they attatched the TPS if it's a S5. They could've put it on the narrow range or the full range, which would cause problems. It's almost sounding as if you may be better off trying to diagnose it yourself.

Its a narrowband tps, I should of written down the numbers myself so I could of verified if its a s4 tps or not.

If I would of known it would of been stuck in the shop for this long I would of never put it in there and would of continued to diagnose it myself. I know I could of probably figured it out since everything I need to know is in the FSM, I have a DMM, and this forum.

Only thing I would of done after checking everything myself is checking the voltages at the ecu write them down then check them in the engine bay, write them down. Then compare with the FSM, and go from there. I would of also cleaned the engine grounds since the ground on the motor looked kind of rusty. Motor pulled great vacuum, and pulled very hard so I know the motor is in good shape, and I did a tune up on it as well to rule out bad plugs.

Now I have no clue how much longer I have to wait till its finished, its been in the shop for over 2 months now. I would of just dealt with the hesitation while I tried to figure it out so I would have something to drive atleast.

I really hate calling him and asking him questions like if he checked the voltages since hes the mechanic and I feel like I piss him off by doing so.

The whole reason why I put it in the shop is because I went as far as I could the tps tested faulty, I found a few vac leaks and sealed them off, but I wanted to have JPR go over it real quick cause I thought he'd know exactly what was up with it and it would of been done within a week or 2 then I would be able to have something to drive.

Did you ever get this resolved?

Sounds like the guy who installed the engine did something wrong. It may be that there is a fundamental incompatibility between the engine and the harness or ECU. Thats not to say you cant fix it.

Is the ECU really the correct one for the engine?

Check for the obvious: are the ignition wires (especially the leading ones) hooked up correctly?

Is there spark on all 4 hi test leads?

Are there any codes?

Does it show a good closed loop test (ECU crossovers from rich to lean abt 8x per sec at steady, non-idle rpm)?

I suspect a sensor is bad, or not wired up correctly (short, ground, open). If none of the obvious things work, I would get down to the ECU and check the voltages on every pip vis a vis those published in the manual. I bet one of them is missing or wrong... top suspects would include the boost sensor, water thermo sensor, mass air flow sensor, crank angle sensor, O2 sensor.

I wouldn't go replacing the entire wiring harness until or unless you find out exactly what signal is not getting to or from the engine, in which case you can just fix the one circuit...

This is a must and will cause your hesitation problems. The vac/boost signal is choppy and pulsing all the time, Without this your pressure sensor won't be able to interpret what is going on. I would recommend installing one, there $2.75 from mazda. Also verify that your MAF is sitting on a correct plane, I have seen ones on a bit of an angle throw off the readings and cause a choppy acceleration on partial throttle. My bet would be on the restrictor pill and or a faulty MAF. Try these or tell your mechanic to try these first before replacing a harness.

+1
Swapping parts gets nothing done. If he cleared the electrical system then why dose he want to replace the harness? After you replaced the TPS did you set it?

Whats S4 and whats S5 for parts on this car? Are the S5 parts propery hooked into the harness? Is it an S4 Harness?