Bert87

Hello all,

After Googling a lot and mainly searching through these forums for weeks, I've finally decided to post about my problem, since nothing I've found really describes my problem precisely enough.

My problem is this: when the car is cold (open loop mode), all is well. As soon as it warms up and has been in closed loop mode for a while, it will begin to "hold back" at WOT, almost as if there's a rev limiter but the RPM limit shifts to a lower value as the engine heats up more. Speeding up is possible, but only if you don't push the gas pedal down too much. Also, it will occasionally stall at idle (very unpredictable when exactly… one moment it runs fine and the next it suddenly stutters and dies).

Now recently, I've replaced my ECM, since the car would die on me at very random times (symptoms were very different to my current ones, also happened on a cold engine). My distributor complete with cap, rotor and ICM had already been replaced by brand new parts (Spectra) and ignition timing was set to no avail in my quest to solve that problem. The new ECM did seem to fix it for a while, but after a few long drives, my current problem came up.

Now as I search for my current symptoms, I find a lot of possible causes. The ones that strike me as likely, are:
-TPS failure (mainly for the idle stalling problem)
-MAF failure (could also be MAF power/burnoff relays, but those are quite new. Sadly, they are Chinese versions by Airtex/Wells…)
-Problem in ignition system (although my coil is a new NGK one and my entire distributor is also new. Besides, wires and plugs are no more than 4 years and 10.000 miles old...)
-EGR problem (although I'm getting no fault codes at all)
-Failing fuel pump or fuel pump relay (although both parts are no more than 1.5 year old. Sadly, relay is again an Airtex/Wells)

I'm really just posting this here hoping that some of you will recognize my situation and tell me about causes and fixes they know may work.
Any advice is welcome!

Some additional info that may help:
-As long as I've had the car, it's been harder to start in warm condition than in cold condition. I've already replaced the coolant temp sensor (not the sender for the gauge, the ECM sensor) and that didn't change anything.
-Since this problem started, I can smell fuel from my exhaust after turning the engine off. This smell can also be perceived from the intake after taking the flexible boot off the throttle body and opening the throttle a bit. Seems to be running rich, but I've not had any codes indicating this. My O2 sensor was replaced 3 years ago.


That's all I can come up with for now… so… yeah… please

mmadden55

Think the o2 sensor might have gone, a rich mix will kill them , you may have a injector sticking open and flooding the engine.

Bert87

I thought the same at some point. However, I doubt that this is the problem, because at WOT, the O2 sensor is ignored as far as I understand. Additionally, why would a leaking injector only occur or cause problems after running with a warmed up engine for a while instead of immediately?

Additionally, I get no error codes relating to the O2 sensor/mixture quality. When my O2 sensor failed a few years ago, it did trigger these codes (don't remember the code number).

Bert87

...Anyone? There's so much knowledge on these boards, surely someone could point me in a likely direction...?

Tuned Performance

iTrader: (92)

You might want to check the fuel pressure leakdown when warm. Typically it takes 5-10 min for bleed down. If it’s faster than that I’d suspect the injectors

Bert87

Right. I just bought a pressure tester (Actron CP7818). Too bad they don't sell those in my country (the Netherlands), so I had to order one from the states. Should be here in about a week... I hope.

I also heard that if a leakdown does occur and it's caused by the injectors, it should be relatively slow. If it's relatively fast, it may also be the check valve in the fuel pump. My fuel pump is relatively new, but still... does this information hold any truth?

I took the car out for yet another test drive yesterday, as well. I can now say that the problem worsens as the car heats up further. Eventually, I couldn't rev further than 1900 to 2000 rpm. If I pushed the gas pedal down too much, the engine would sputter and almost stall. Also, when idling, I could rev the engine once, but upon attempting a second rev close to the first, the engine hesitates badly as well.

Does this new info give anyone an additional clue?

Tuned Performance

iTrader: (92)

Is this the right eBay for the Netherlands ?
https://www.ebay.nl/itm/US-PRO-by-BE...UAAOSwVVRaes8K
The fuel rail fitting is an4 which should come in the kit
Sounds like your running rich but I’m not sure why. Or you catalytic converters could be plugged.

79Daytona

Well this maybe a long shot but what about the fuel pressure regulator .

Bert87

All right, well it's been a while since I last posted but I have an update. I bought a fuel pressure gauge and performed a few tests. First, I connected the gauge and primed the fuel pump. It showed a nice 42 psi and held it for 5 minutes. Then, I started the engine. Pressure dropped to 35 psi and climbed to 42 when revving, which fell back to a steady 35 when kept at a constant rpm.

I allowed the engine to heat up and turned it off. Fuel pressure was kept for 5 minutes. However, after 10 minutes, suddenly the pressure dropped to 20 psi!
I primed the pump again and carefully watched the gauge. Now the pressure was very slowly decreasing and after 5 minutes it had decreased from 44 psi to 40 psi. 5 more minutes and it was well on its way to 30 psi. It was now clearly dropping and the longer I waited, the faster it seemed to drop.

After another identical test cycle confirming the same results, I ran the engine again. Behaviour with the engine running was identical to before: 35 psi, when revving up to 42 and then slowly back to steady 35.

After shutdown, the pressure seemed to hold for a while longer... but then proceeded to drop down again, all within a time span of about 15-30 minutes.

I checked the vacuum line on the fuel pressure regulator for fuel. There is no fuel in there. So... leaking injectors? Or maybe fuel pump check valve (which I doubt, since my pump is only about 1.5 years old and it's a Carter replacement, which should be of decent quality).

Any thoughts at this point?

Tuned Performance

iTrader: (92)

Bert87

Yeah, although me being in the Netherlands isn't going to make sending the injectors to Southbay very financially efficient
However, I'm also getting to the point where I think the only way to really check is to remove the fuel rail with the injectors still attached and simply see what happens.

One thing I can't wrap my head around just yet is why one or several leaking injectors would cause this problem that only occurs in a hot engine and gradually gets worse as you drive along/warm up more. Does that even make sense? Will a leaky injector leak more when warm (possibly due to lower viscosity of the fuel...?), to the point it screws with your mixture so badly you can't rev past 2000 rpm? And if so, why on earth doesn't this trigger an SES light for O2 sensor or something else?

Another possible cause I'm finding a lot is the ICM. I even found a post on these boards where a user called "FSTFBDY" wrote described an identical situation to mine in his buddy's car: runs fine cold, after heating up eventually won't rev past 2000 rpm. It's the 4th post in this thread:

https://www.thirdgen.org/forums/tech...on-module.html

My ICM is new, but I have had a failed alternator recently (rectifier broke) which I have replaced. Perhaps this took out the ICM before I replaced it...?
Might order a new one since they're not too expensive, see where that gets me.

I'd love to get some insight on how the injectors could cause these symptoms, too. Has anyone got a good explanation for me?

southbay08

you can pull the plugs as well...if any of the cylinders are wet your injector/injectors are leaking

Street Lethal

iTrader: (16)

Bert, you may not want to hear this, but you have to datalog. Suggestions are great, but a datalog will underline what the problem is. You need to invest in tuning equipment, or a datalogger, otherwise you're going to chase your tail doing every little thing to try and fix the issue. A simple datalog will tell you what each and every sensor is doing at any given point, as well as your air/fuel ratio, and spark. It will underline it.

- Rob

Bert87

That sounds like an excellent suggestion, but to be honest I do not know where to find the equipment to do that. Could you point me in the right direction?

Tuned Performance

iTrader: (92)

Bert87

Thanks! That's reasonably affordable considering it'll help me troubleshoot this car for the rest of my ownership.
I think I'll actually invest in this cable before ordering any other parts (sorry for now, southbay08, who very kindly replied to some of my email inquiries really fast today...).
No point in asking for advice if you're unwilling to take it, right?

Edit: I just ordered the datalogger. It'll probably take quite a while to get here, but it's a start. I'll keep you updated.

Macarchie

As a data point... I have a blue '87 Formula, 305 with a 5-speed. Last year I had the stall / no power issue and it turned out to be the vacuum lines under the fuel canister. The canister is behind the right headlight. The vacuum line that passes under the canister had dissolved over the years. Easy to fix. Hope this helps.
- Jimmy

Bert87

The very interesting to know! But are you sure there is a vacuum line that passes under the canister? I only know of the lines on top.
This picture shows the lines I'm familiar with (not on my car, but mine is the same):

https://www.thirdgen.org/forums/atta...7-dsc02552.jpg

Is there an additional one?

On another note, your reply has given me another idea for a possible cause of failure. As my old vacuum lines seemed a bit worse for the wear about a year ago, I replaced a lot of them.
Since rubber lines like the originals are hard to come by here in the Netherlands (I asked several autoshops, none still had them in stock) I opted for silicone replacements.
I ordered them from a website known for supplying parts for higher-performance and track cars, as these hoses seemed to be thicker walled, thus minimizing the chance of them collapsing.
However, what if one of the lines is collapsing under heat anyway? Might explain my problems... hotter it gets, the easier it collapses and the more I press the gas, the more it collapses as an effect of the additional vacuum.

I may have to order some new rubber vacuum lines from the states to try if that makes any difference.

79Daytona

Well you may want to check the vacuum line on the EGR valve. On my 92 z28 5.7 I found that my was not hooked up and it made it kinda run weak and idle weak from time to time when in drive.

Bert87

Checked it, along with all vacuum lines. All are connected just fine. No apparent leaks anywhere.
Man I wish overzeas shipping would go faster. I can't wait to start datalogging and hopefully get to the bottom of this problem.

79Daytona

I understand how you feel.

Bert87

The datalogger has arrived! Sadly, I've been unable to take the car out for a drive due to bad weather, but I logged during idle. Here are some results:
Screenshot of sensor data before revving, engine not warmed up.
Screenshot of flag data, engine warmed up. Note the rich flag, which intermittently occurred.
Screenshot of sensor data after revving, engine warmer.

Now I've noticed a few things, myself:

-I needed to use the 10K mode on the datalogger to be able to get data. However, this clearly had an effect on the operation of the engine.
The RPM's increased and it seemed to start to run a bit more irregular. As soon as the datalogger was disconnected, this effect stopped, and it came back just as quickly upon reconnecting.
Is this supposed to happen? I imagine it will seriously affect the quality of the logging!

-I kept getting a rich flag, even when closed loop was obtained.

-The O2 signal was constantly moving between 0.3V and 0.8 V. I don't know what voltage rich or lean is, but it was very unstable.
This happened at idle and while increasing rpm to about 2000 by applying the throttle.
I'm not sure if this is normal (I'd think not) and if it's caused by the datalogger being connected or not, as this did cause audibly more irregular engine operation.

-Apparently, my TPS was maladjusted. I adjusted it quite recently and haven't checked it since. My DVM confirmed what WinALDL was telling me: it needed adjusting. So I adjusted it back to 0.54 V.
Could that be (part of) the explanation for my troubles?

I'll be taking the car out for a driving while logging soon and report back after that. If any of you can already see or determine something based on these results, please let me know!

Bert87

OK, busy day today. I've done the following things:

-Replaced the ICM, distributor cap and rotor for Standard Motor Products parts. I was shocked how much bulkier the contacts inside the distributor cap were in the new SMP one!
I figured with this, the ignition parts should be functioning properly.

I took the car for a drive. After confirming that all seemed well, I started a log as reference point. I accelerated at WOT to have some reference data. Then i stopped logging as my car really doesn't seem to want to run nicely in ALDL mode (at constant cruising it seems to misfire a bit, which stops the moment I remove the ALDL plug). Then, I drove until, alas, I encountered my problem once again.
Under acceleration, the engine would just stop revving higher at some point. I reconnected the datalogger, started a new log and made sure to accelerate a few times at WOT, triggering the problem while logging.

All this has resulted in some datafiles than I can share. I've put them into Excel and isolated the data that was stored during the accelerations for comparison purposes.
I must say I'm a bit disappointed with the logging interval of the system. I was expecting more data points per second. As a result, I feel the behaviour doesn't show itself quite as clearly as it should.
I am definetely going to need some help in analyzing these files as I'm new to it, but here are my 2 cents on what I see.

Signals that seem in order
-TPS signal seems OK, although it never goes higher than 90%.
-MAF signal seems OK, as well. It increases as engine speed does. Highest value is around 150 g/s.
-Coolant temperature seems to be in order.
-MAT, for as far as I can tell, seems OK too.
-EGR goes to 0. I reckon that's as it should be.
-There are no error codes. Of course, I already knew that as I'm not getting an SES light.

Signals that I'm not sure about
-O2 goes to 0 mV under WOT. I suppose this is the ECM ignoring this signal... can anyone confirm?
-BLM is all over the place. During one troublesome acceleration, it was around 84 (so shortening injection time), but during the second it was around 214 (so enlarging injection time).
-the BLM table shows more data over 128 than under it, and mostly in the wide area. The narrow table stayed quite empty. Am I right in assuming this means my injectors are probably not leaking, as there is not constantly fuel being removed (BLM/INT lower than 128)?

All in all, I haven't found anything obviously wrong with my datalogging.
I could very much use the help of someone with more experience in this area to take a look at my data and tell me if there's anything else than can be deduced from all of this.

So, could you guys please give me a way to provide you with the data and take a look?

Edit: managed to take a picture of the important part of my Excel sheet. The green lines are from an acceleration when the fault was not present.
The red lines represent 2 accelerations where the fault was clearly present. Especially the second one shows the RPM "locking up" around 3650.
This could very clearly be felt in the car as bogging down. It seems to "want" to accelerate more, but is blocked somehow.

Again guys, I'm in dire need of help now. I feel like I will not be able to proceed anywhere on my own from here.

Bert87

So I've been looking through the data, searching online for the meaning of each signal.
What I've find is there are some vast differences in INT and BLM for RAW and Sensor type data.
BLM RAW data seems to be on the high side, averaging out at about 135. The Sensor data for BLM doesn't show this.
Strangely, it does drop back down to 128 during the troublesome accelerations.
Besides the O2 dropping to 0, there are no other strange things I can find in my data, myself.
I've been using ALDLview to go through all of the signals, as well.

Still hoping for one of the previous contributors to help me check the data!

T4Turtle

T4Turtle

T4Turtle

I was looking information up on my issue on Identifix.com and they show a confirmed fix was injectors with your issue and they also saw 0 voltage at WOT on the O2 sensor. Might want to get a good look at the injectors here.

Bert87

Thank you T4Turtle for your feedback.

Since my last post I've actually been doing some things.
I've found that our cars have a problem with the fuel pump overheating and therewith having cavitation occur, leading to loss of fuel pressure.
Since my pump is relatively new, I decided to root around the car to look for anything that would make the fuel pump run hotter than normal.

For one, I found a piece of fuel supply line right before the fuel filter that was very clearly pinched. It was probably twisted at some point when the fuel filter was replaced.
This would add significant resistance to the fuel pump and, as my pump is quite new, it makes sense to me that the cavitation would eventually wear a pump down, leading to an increase in severity of this issue.
I replaced this fuel line with a new one thus eliminating the pinch.

Second, I took my fuel tank breather valve (vent) off. It was very dirty, so I took it apart and cleaned it as shown in this wonderflly clear video:


After all of this, I took as test drive (the fuel pump is still the same one). Last time the complaints started within half an hour or about 30 miles of driving. This time, I drove for over 2 hours and about 80 miles altogether and only noticed a very slight hesitation at full acceleration at the end of the RPM range (around 3700 til 4500). This happened after I drove through town for a bit at lower speeds. Data logging showed that MAT rose during this time.
After some driving at higher speeds, this hesitation lessened to the point of almost disappearing. And wouldn't you know it, the MAT dropped again, too.
On a side note, O2 still fell to 0.000 at WOT (or close to it, let's say TPS signal above 85%)

Since the fuel pump problem is temperature related, I decided to take a look at those.
During my previous, more problematic drive, I noticed that my MAT would rise to about 160 degrees Fahrenheit. Coolant temperature averaged at about 200 degrees Fahrenheit.
During this new drive, I couldn't get it higher than 125 degrees Fahrenheit, except by idling exceptionally long, but upon driving again the MAT would quickly fall back to this 125 or below. Coolant temperature averaged at about 195 degrees Fahrenheit.

I don't have a full explanation for this difference in temperature. During my last drive, it was daytime, outside temperature was about 73 degrees Fahrenheit and the sun was shining.
During this new drive it was evening, going on nighttime, with temperatures going from about 60 to 50 degrees Fahrenheit.
I don't think that difference in ambient temperature fully explains the difference in MAT.
I am theorizing that my engine might have been running so lean last time that the combustion in the engine ran hotter, thus heating up the MAT sensor and of course coolant more, as well.

Next weekend, some nicer weather is in the forecast, similar to the last time I drove. I intend to take the car out for a drive again, datalogging and all.
I hope I'll see similar succesful results to last time. I think my engine still has some trouble getting enough fuel at times, but if I can at least cruise indefinetely without problems, revving until approx. 3500 rpm without hesitation, I would deem the car properly driveable for now.

I will keep you updated!

P.S.: My engine runs somewhat crappy in ALDL mode. I've had it stall at idle and sputter while cruising at lower speeds and overall just feel that the added ignition advance in ALDL doesn't make the engine run smoother. I wish GM hadn't implemented this behaviour!

T4Turtle

Your welcome Bert87. Still worth a quick resistance test on the injectors, they might test good or there may be some that are obviously off, they all should be close to one another around 12-15 ohm range. This will not be conclusive as they could be bad ad still ohm out OK as is the issue with mine now. I had to run a scope to be able to see the lack of fuel type of misfire. My car runs and drives great with decent part throttle power then falls flat when I go WOT.

Bert87

I forgot to mention that I already tested that in the past. They were all around 16.5 ohm with no more than 0.1 ohm spread between the 8 injector coils.
You mention they should be 12-15, but I've found several sources that state 16-17 is where they should be for stock injectors.
Some aftermarket injectors do seem to be more in the 12-15 range.

Example source: https://www.thirdgen.org/forums/tpi/...injectors.html

Again, considering the complaint and datalogging (BLM increasing as engine warms up, O2 dropping to almost 0 under WOT while oscillating normally under lower load) it seems lack of fuel is still somewhat of a problem for me.
Because the replacement of the restricted fuel line brought on such a difference, I'm under the assumption that my fuel pump running warm and having cavitation issues due to the restriction was part of my problem.

My current fuel pump is a CARTER P74006, which is a rotary vane type, which is a positive displacement type of pump. These are known for failure under higher temperatures and susceptibility for cavitation.
Because of this and the fact that it may already be damaged from cavitation, I decided to replace the fuel pump with a BOSCH 69218, which is a turbine type pump.
This type should be more durable and less sensitive to higher temperatures. Also, I didn't pay too much for it on Rockauto.com, so it's better safe than sorry.

When I get the new fuel pump I'll install it and take the car out for another test drive. I'll let you know what happens.

T4Turtle

If the fuel pressure at WOT matches at idle with vacuum line to regulator disconnected then it should be fine, this is the best way to test this under full load. Have you done this?

If you have a pressure tester that has a purge line you can also do a fuel volume test to make sure the volume is there as well.

If that all checks out then it is down to ignition or injectors. Can you borrow a lab scope?

Tuned Performance

iTrader: (92)

Bert87

I read that idle RPM goes up and timing advances (you say it locks, though?), but since there seems no other way of datalogging (I get no datastream without the 10k resistor, not even after switching it off on the Moates cable after communication has already been established). If I can't drive the car with datalogging on, then what good will it do me? My complaint occurs only while driving, so that's the data I'd want to see. And considering the fact I've seen several people's WinALDL logs on various forums that were all taken while driving their TPI cars, I figured that's simply the way to go.

Should I be logging in another way?

Tuned Performance

iTrader: (92)

Bert87

I think I got it! For now...

So, in a nutshell, this is what happened

-In my data logs (taken in ALDL mode, which I have now learned is not the correct way but that's how I did it at this point), I saw BLM increase over time as I drove. Conclusion: apparently the engine is keeping the injectors open longer as everything heats up, so for some reason it is getting more difficult to inject sufficient fuel.

-I found information such as this website: http://fuelab.com/what-is-cavitation-how-to-avoid-it/ and suspected fuel heating up might have something to do with my problem

-I found a restriction in the feed fuel line right by the fuel filter under the car. Resrictions in feed lines are possible causes for cavitation/vapour lock conditions. I replaced this section of fuel line.
*Result: a much more succesful, problem free drive, with only some missing power in the higher RPM range after idling and driving slow a lot (thus, heating everything up).

-I replaced my Carter fuel pump by a Bosch turbine style fuel pump. I feared my Carter unit might have been damaged by cavitation somewhere in the process.
*Result: I took a loooong drive in higher temperatures with the sun beaming down, made sure to cruise and idle a lot to heat the system up well.
Even at the very end of this drive I had no more bogging or missing power anywhere in the RPM range!

For now I'm very happy with this result. I'm probably going to risk going to a car show or two sometime soon to put it to the test even more.
I will keep you all posted.

I'd like to thank everyone that has contributed or tried to contribute to solving my problem in any way, shape or form.

Bert87

Back again with a final update!
This weekend, I went to no less than 2 car shows. I drove upwards of 300 miles altogether, drove in a slow-moving parade and even had to let the car idle for a while as I nearly drained my battery (did I mention I have a KITT replica? Those halogen scanners sure do drain a battery! )

And what do you know? No more engine trouble. None. All it took was the removal of a restriction in my fuel line and a new fuel pump.
I would've never found this out if it wasn't for datalogging (even though I did that in ALDL mode, which I'll try not to do anymore in the future...)
I'm still rooting for this improvement to stay intact, but for now it sure does seem like this issue was solved.

Again, thanks to everyone who helped or at least tried to do so. You're all wonderful people.

And to end on a positive note: here's some footage of me driving in the parade: