I've been having a hesitation problem with my 88GTU. As it turns out my hesitation problem is due to the secondary injectors not firing. They work sporadically, causing what feels like hesitation but is actually the injectors coming on briefly, causing small bursts of acceleration.

So far, I've checked the TPS, CAS, injectors, boost sensor (found that I grounded it unnecessarily and removed the ground), and replaced the injector connectors (the originals were cracked and bits broken off). Apart from this issue, it starts right up, with no flooding, and will pull to redline.

I'm planning to tear apart the engine harness and build a new harness, retaining the needed wiring for the factory components in a way that would be easy to pare down later. This will pave the way toward a MegaSquirt, where I'd simply lope off the OE ECU connectors and create a pigtail harness.

The fuel injectors were originally 460cc high impedance. At some point in the car's life, someone replaced the secondaries with low-impedance--which I later corrected with 10ohm 10-watt resistsors inline. Later, I replaced the primaries with low-impedance injectors with resistors soldered in-line.

Two of the injectors are reman units (the primaries, which are perfectly fine). and the remaining two (the secondaries) are the older units that were cleaned back in 2006 by Marren Fuel Injection. All Ohm values are within factory spec.

Here are my questions:
1. As the car was ran with two incorrect injectors until 2006, could the incorrect values have damaged the ECU's injector drivers causing sporadic operation under load? If so, how could I test the ECU?

2. Could old wiring be the cause? I tore apart the harness years ago, cleaned up the wires, replaced all the unsealed 1/4" female quick disconnects with new ones and re-wrapped the harness. Could there be a break in the wiring leading to the secondaries?

3. Are there other sensors that, if they are bad or have no connection, cause the problem? I have yet to test the water temperature sensor or the atmospheric sensor in the interior.

 

maybe a long shot but check the current from the alt to the battery and whats your voltage on your dash board?

 

Pin 3H of the ECU is the front secondary and the wire is Light Green/White. Pin 3F is the rear secondary injector which is Light Green/Red. Disconnect the smallest sized plug on the ECU which houses these two wires and also disconnect both secondary clips/wiring and do a continuity test on them.

To see if the ECU is sending the proper signal to the secondaries to fire them you will need an LED light. Take the light to the battery first to determine which is the positive wire and negative wire to the LED. Then with the smallest plug to the ECU plugged in, place the negative LED wire into the back of pin 3H, front secondary, and then place the positive wire of the LED into the back of pin 3I, Main relay which supplies voltage, and with the car running rev the engine to 4000 rpm or so while the Pressure sensor vacuum tube is disconnected and plugged, and in addition to the TPS being disconnected to simulate load and the LED should blink repeatedly in a rapid manner to indicate that the ECU is firing the injector. Do the same for the rear secondary as well.

 

Before I put the car away, voltage appeared to be at normal charging level. The alternator is a GM CS130 140AMP unit that I adapted to fit (and working perfectly).

Thanks for the advice satch, I'll be checking on that.

 

Has anything come of you problem? I have the same thing going on and was wondering the outcome of the two suggestions. Has your problem been fixed and what fixed it?

I am trying to find anything I can to get closer to the problem I am having. It's doing pretty much exactly what you are describing. It's totally random firing of the secondary injectors under load. Sometimes they work, sometimes they don't. So far the best I have to explain this is hitting hard bumps or taking corners sharp tends to change whether or not they function.

Thanks

 

Currently, the car is in storage, and I'm not going to be working on it until January. I have other unrelated projects, and the work I have planned for the car is going to take some time gathering up parts and supplies. The plan is in January (or sooner), to do the continuity test on the harness, and, if the wiring is okay, run the engine to check the ECU.

If it's not the injector wiring, sensors, or ECU, it could be wiring for another sensor. If you unplug the boost sensor, the secondary injectors will not work at all.

 

Okay, I finally did a continuity test on the ECU harness. Both secondary injector wires (LG/W and LG/R) tested fine, including the supply (B/Y). So, the next step is to check the ECU, which means running the engine.

Also check continuity on the boost pressure sensor and it checked out fine too.

When the engine is running and I do a load test out of gear, above 3500RPM, both injectors will fire very intermittently. They'll go on for maybe less than a second at a time and at different RPMs.

I should also add that I had incorrectly grounded the boost pressure sensor ground--and removed the ground later on. Could this grounding had damaged a sensor or the ECU?

 

Another update: I pulled the MAF sensor from the car and checked it per the FSM. Everything was within spec, but then I tested the flapper door. While it is within spec open (260) and closed (67), I noticed that it would go out of range, past 500 ohms, as I opened the door. Plus, the value would fluctuate as I opened the door.

 

Actually, the Air Flow Meter is completely within spec. When testing the pointiometer, using an ohmmeter only, it's normal for it to fluctuate.

Following this test http://www.nopistons.com/forums/topi...w-meter-check/ using a DC voltmeter and a 5V power supply (a 5V AC/DC adapter for a circa 2002 Linksys Router), I found the AFM was within spec, 4V closed to 0.40V open. So, the AFM is fine.

 

Another update. Checked continuity on the AFM wiring, fuel pump check connector, water thermo temp, intake air temperature sensor in the UIM, and the CAS (as well as ohm values on CAS itself). It all checked out. Although I'm starting to think that a continuity test on a 22-year-old wiring harness means less and less to me.

Question about the IAT in the Upper Intake Manifold: when an ohmmeter is attached, what reading is expected? I couldn't find anything in the Fuel and Emissions, Body Electrical or Wiring Diagrams sections of the FSM.

 

Okay, I pulled the ECU to check for cold solder joints and damage. Turns out, resistor 951, which is connected to the port air solenoid valve, has burned out. No reading at all. The traces on the circuit board still have continuity. I checked the solenoid for damage, and at first though the wires had melted, but after pulling off the old plastic sheathing, the wires appeared fine.

It also looks like some burning, or simply discoloration on what appear to be the injector drivers. Can anyone explain what the green rectangular components are? All four are marked 334K100 NCC A. Are they the injector drivers? Is there a way to check them without running the engine?

So, it seems the problem is with the ECU.

 

Usually if you turn the key to ON and then check each pin on the ECU by backprobing the individual wires, you can determine if the inputs/outputs to the ECU are good/bad. See CONTROL UNIT in the FUEL AND EMISSIONS section of the FSM.

Port air solenoid does little to nothing in life. Take my word for it.

How did you do the LOAD test you described? In detail please. Sitting in the driveway and did a LOAD test is what I read.

Also...........have you ever thought about doing this. Connect your meter to either of the secondary wires at the ECU (backprobe them). Then go for a drive. The secondarys should read batt voltge when not under load. When you step on the pedal all the way and go over 3500-3800 rpm the voltae should make a dramatic drop down to ???? depends. Usually around seven volts showing they are firing .

 

Before I put the car into storage, I did the load test by warming the engine up to operating temperature by driving it. Then, I disconnected the TPS and the vacuum hose from the boost sensor.

I ran the engine and used a sound probe to check if the secondaries fired or not. They fire intermittently, like there's a short or a faulty component, or maybe a sensor feeding incorrect information. When driving, the problem manifests only at high-RPM, and like it was hesitation. Only, it actually gives you short sudden bursts of power because the secondaries suddenly come on for maybe a second at a time.

I do take your word for it, but I wasn't sure about the port air solenoid, hence the reason I asked. One of the systems that you check in the FSM is the air control valve.

Unfortunately, right now, it's winter, the car is in storage, and I really don't want to run the engine until I've eliminated as many other systems and wiring as I could. The burned out resistor in the ECU makes me think that there may be other damage. The car also ran with incorrect impedance injectors (only one pair, though, which turn out to be the secondaries) for who knows how long until I had them out for cleaning during an engine rebuild and put in 10w10ohm resistors in-line.

The problem started at some point after installing a CDI ignition box while in storage during another Winter years ago. I mistakenly thought it was hesitation and lived with it until I realized I was wrong.

Correction: The primaries were the wrong impedance, the secondaries were the correct high-impedance ones.

 

I've made some progress. After eliminating the major parts of the wiring, the CAS, the AFM, and various other sensors, I finally looked at the ECU.

First, given that I found a burned-out component in my original N327 ECU, I decided that I should have another ECU as a spare and to a provide a point of comparison. I found one on eBay for really cheap, found that it had no sign of damage and showed no codes upon turning the ignition on. I plugged the N327 back in and it showed a code, but I couldn't figure out what it was.

Hailers, I followed your advice and checked the ECU pins per the FSM (note, checked with ignition ON and the engine COLD, not warmed up).

I started with the N327, and noted any readings that seemed suspect. One reading in particular stood out: pin 1U - output, Coil with igniter (Trailing IGs-T (Select Signal). The N327 read 0.00 volts, whereas the N326 replacement read 4.29V.

After double-checking both ECUs, and the N326 otherwise showing the same values as the N327, I decided to button up the interior.

Now, as mentioned previously, I haven't test run the engine, and won't until April at the earliest, but I think that the problem in my case turned out to be a damaged ECU, which was caused by crossing the battery cables many years ago. Now, how the car still ran or not blow the engine despite this I don't know.

 

is there a stock resistor pack on the wiring harness(under the air box)?
.also,have you checked to see if the auxiliary ports(5th/6thports) are actuating?

 

86-87 have the resistor pack, mine is an 88 and had high-impedance injectors from the factory. Oddly, when I got the car, I found the two primaries were low-impedance, but only learned about that after sending them out to be cleaned back in 2004. 10-ohm, 10-watt resistors are now spliced in-line between the injectors and the ECU.

The Auxiliary ports do work. One side was seized, but I pulled, cleaned and sorted out the problem long ago.

 

Any update?

 

Only that I've decided the ditch the factory system and put in a MegaSquirt3. Either there was a sensor that was faulty that looked ok or I had another bad ECU. Either way, I got to the point where I couldn't justify spending more time and money fixing a 20+ year old system whereas I could put in a new one that could be more easily diagnosed.

 

I just found something when I removed the LIM to install the Atkins Designed Six Port Actuator Valve Kit. You should be able to operate the 5th/6th port actuator valves with your breath; well, they didn't budge. I tried my air compressor with a low PSI, and still nothing.

So, I pulled off the actuator valves and found that their air passages were clogged with silicone sealant. I used too much sealant -- or sealant where I shouldn't use it -- to install the actuator valves. So, the engine never had a chance to run lean, but rich.

Therefore, here's what I think the problem was: with the auxiliary valves not able to open, the engine didn't get enough air at high RPM, so the air/fuel mixture was rich. The ECU cut fuel from the secondary fuel injectors to keep the air/fuel mixture from getting too rich.

So, there's my problem, which I found too late after tearing down the motor and committing to installing the MegaSquirt.

 

Figured it out! Turns out the JSPEC ECU was bad! I swapped my N332 in there an now it revs to 7k! thanks for the help everyone.

 

I am wondering the same thing.

I am about to buy a Turbo II and the secondary injectors do not open, the owner is running a stand alone ECU (Micro Tech.) Would a good tune fix the problem?? I can't have this be anything serious