Hesitates, running rich and what I’ve done so far. Any other ideas?

[Crispyc21]

Car: 1990, auto, 73k.

I’m thinking injectors might be the next thing for me to check. But before I go replacing them I would like to hear some ideas.

I’ve been fighting a hesitation while accelerating. It’s fine at WOT and idles smoothly. The hesitation has been getting worst over time. At first there were no codes. So I had the IAC and TPS adjusted to stock settings. I checked fuel pressure..42#, but then drops to around 30#s in 20 min. Sometimes it drops quicker and sometimes slower. So I changed out the fuel filter and pump (they really did need it). It idles nice and smooth now but still hesitates. Finally while driving it starting hesitating badly and the SES light came on then went off after about 30 sec. I was actually happy because now I had a code to work with. It was code 45, running rich. I threw in a new O2 sensor because it was quick, easy and cheap, but it didn’t help anything. The code is not always there. It only showed up that once when it got real bad. But the severity of the hesitation varies from time to time.
I am thinking injectors because of the fact that I’m still losing pressure and running rich at the same time. Yes those could be two different problems, I just don’t know how likely that would be. I have an adjustable fuel pressure regulator (previous owner installed) and I’ve played a little with the fuel pressure but nothing helped.

My next bright ideas!!

I’m looking into my TPS a little more because when I was checking the voltage, making sure it sent smooth numbers while the throttle opened it wouldn’t go back to .54 right away. At WOT it was about 4.05. When I let go of the throttle it would hold at .7? for about 15-20 sec. then go to .6? for another 20 sec. then finally back to .54. Plus I checked the bottom wire that is supposed to be 5v (I think) it only registered 4.45v.

One other thing I’m going to do is clamp up my return fuel line to see if the pressure still goes down that quickly.

I’m also going to try to remove the spark plugs to see how they look. I think that will give me some indication if the fuel injectors are leaking.

I'm open to other ideas. Just remember I'm not a mechanical expert and need things explained very simply. I have a shop manual but I’ve never done this stuff before.

 

[DRTH VTR]

I would be surprised if buying injectors would do anything besides empty your wallet. I think a proper diagnosis would keep you from randomly throwing parts at it. I have found that using a professional is cheaper in the long run. Just my $0.02

 

[Crispyc21]

I would be surprised if buying injectors would do anything besides empty your wallet. I think a proper diagnosis would keep you from randomly throwing parts at it. I have found that using a professional is cheaper in the long run. Just my $0.02

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I'm not buying the injectors just yet but I'm open to ideas of what to check. I've been trying to diagnose things the best I can with my very limited tools. That's the big problem is my lack of scanning/testing tools. I haven't taken it yet to a professional yet because I am trying to learn as much as I can about this stuff. I don't mind replacing the little stuff for cheap as long as I learn something while doing it. But I will not replace anything that expensive before I get a professional opinion. With the injectors it's usually cheaper to replace them all then to pay for the labor for testing, cleaning and all that jazz.

 

[MoeJr]

Change TPS. Sounds to me like it is getting lazy.

 

[JOliver]

Car: 1990, auto, 73k.

I’m thinking injectors might be the next thing for me to check. But before I go replacing them I would like to hear some ideas.

I’ve been fighting a hesitation while accelerating. It’s fine at WOT and idles smoothly. The hesitation has been getting worst over time. At first there were no codes. So I had the IAC and TPS adjusted to stock settings. I checked fuel pressure..42#, but then drops to around 30#s in 20 min. Sometimes it drops quicker and sometimes slower. So I changed out the fuel filter and pump (they really did need it). It idles nice and smooth now but still hesitates. Finally while driving it starting hesitating badly and the SES light came on then went off after about 30 sec. I was actually happy because now I had a code to work with. It was code 45, running rich. I threw in a new O2 sensor because it was quick, easy and cheap, but it didn’t help anything. The code is not always there. It only showed up that once when it got real bad. But the severity of the hesitation varies from time to time.
I am thinking injectors because of the fact that I’m still losing pressure and running rich at the same time. Yes those could be two different problems, I just don’t know how likely that would be. I have an adjustable fuel pressure regulator (previous owner installed) and I’ve played a little with the fuel pressure but nothing helped.

My next bright ideas!!

I’m looking into my TPS a little more because when I was checking the voltage, making sure it sent smooth numbers while the throttle opened it wouldn’t go back to .54 right away. At WOT it was about 4.05. When I let go of the throttle it would hold at .7? for about 15-20 sec. then go to .6? for another 20 sec. then finally back to .54. Plus I checked the bottom wire that is supposed to be 5v (I think) it only registered 4.45v.

One other thing I’m going to do is clamp up my return fuel line to see if the pressure still goes down that quickly.

I’m also going to try to remove the spark plugs to see how they look. I think that will give me some indication if the fuel injectors are leaking.

I'm open to other ideas. Just remember I'm not a mechanical expert and need things explained very simply. I have a shop manual but I’ve never done this stuff before.

I just went throught the same thing with my 90(102k miles) changed everything ...went on for about 6 months...they told me that the SYS ment the battery or alt was going out so I replaced both same thing .....FINALLY I replaced all the sensors and kept hoping then last resort I changed the ECM and it fix my problems totally ..The reason your loosing pressure and its running rich is more than likely because its going into "limp mode" .Limp mode is fuel goes high timing goes retard.I got one from Advance Auto(couldn't find a better) plus at 95 bucks it was worth a shot...it worked.I will more than likely find a better replacement one day but hey its working fine now.I took all my orginal stickers off my old ecm so it looks factory.
Don't know if this will help but don't rule out the ECM.
If you try it and it works I'd love to know...email me if it does.

Jason
VetteInstruments@aol.com

 

[WhalePirot]

Cars with serious leaks and running problems often seem to run great at WOT.

There is a leakdown spec for the injectors, but I cannot recall it.
Have you tried resetting the ECM (pulling power from it for at least 10 seconds? Allow it to relearn or a while driving.

Check the book and set your fuel pressure to factory spec; likely 45 psi. I believe the vacuum line should be pulled off for this setting. i wonder if the diaphram inside it is bad, should your pressure checks fail.

Spark plug analysis is always right on!

Checking your manifold vacuum?.Any leaks from a low reading? Hisses? Low manifold pressure will tell the ECM that the engine is under load and needs more fuel. A hotter camshaft can do this, too.

 

[hsz33]

Change TPS. Sounds to me like it is getting lazy.

I have similar problem with the rough idle can you please clarify what TPS is? Thanks

 

[Huskerman]

Throttle Position Sensor.............

 

[djsroknrol]

Could be the ignition as well....not a strong enough spark when you get on it and it stumbles

 

[vigman]

Are the plug wires original ?

Could be arcing.. that would cause a stumble

 

[Schrade]

I have similar problem with the rough idle can you please clarify what TPS is? Thanks

If the solution wasn't in the old thread (good job searching BTW), maybe start a dedicated thread...

Plug N PRay new parts, aka Fully Automatic Assault Wallet repair technique, as moejr suggested in 2004 didn't, doesn't, and never will work.

 

[John Robinson]

I have similar problem with the rough idle can you please clarify what TPS is? Thanks

Hope this sheds some light on thetps for you

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ThrottlePosition Sensor (TPS)
Copied from 1993 Service Manual​

The Throttle Position sensor (TPS)is a potentiometer connected to the throttle shaft on the throttle body. It isa potentiometer with one end connected to 5 volts
from the ECM and the other to ECM ground. A third wire is connected to the ECMto measure the voltage from the TP sensor. As the throttle valve angle ischanged (accelerator pedal moved), the voltage output of the TP sensor alsochanges. At a closed throttle position, the voltage output of the TP sensor islow (approximately .5 volt). As the throttle valve opens, the output voltageshould be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fueldelivery based on throttle valve angle (driver demand). A broken or loose TPsensor can cause intermittent burst of fuel from the injectors and cause anunstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensorcircuit is shorted a DTC 21 will be set. A problem in any of the TP sensorcircuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use adefault value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than totell me the ECM was bad.

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