I notice when I'm cruising at part throttle, the car seems to stumble slightly or surge. When I give it more than half a pedal though, it doesn't occur. Could this be a TPS problem? My ignition stuff is all pretty new.

thanks

 

I'm having similar problems.. I wish that I had a data logger because I could get a better idea of what's actually going on. Mine seems to be timing related, but I'm not entirely sure that it is the source. My TPS seems to be spike free and it's set at spec. All my ignition stuff is fairly new as well..

 

i'm with you guys too. everything is cool in park, but when i put it in gear and push the pedal it stumbles and bogs down when i go to WOT. My TPS is cool and i just set the idle with the IAC. Next on the list is fuel pressure adjustment by means of the O2 sensor. If that doesn't fix the problem, someone is getting a bullet. well not really, i'll just blame it on the tranny cause its struggling too.

 

Sounds like a TPS with a bad spot. Put a meter on tps and read the center wire voltage it should change smoothly when you open and close the throttle. If its bad it will jump to +5V or 0V in spots usually just off idle.

 

Thanks..I think you're right. I bought a new one yesterday. Is the voltage preset or does it have to be set?

 

Just install it i Don't think there is a mechanical adjustment on your motor...

 

actually you adjust it with the mounting screws. put it on at closed throttle it should read 5.4 volts. if not rotate it until it does then tighten the screws. Then slowly open it to WOT and make sure the increase in voltage is uniform.

 

Yeah, but is it necessary if its new?

 

Oh yea it matters. You can still have the same problems with a new if it is not installed correctly.

 

Yeah, but do any of you guys have a more simplified explanation than the one on the Tech Page for adjusting it? I've never read a voltmeter and I'm not sure what a jumper wire is or where to put it. There's 3 wires that I can see.

thanks

 

i had the same problem but it would somtimes die out when it stumbled. i just replaced my ignition modual and it seemed to fix it but it somtimes stumbles when i slow down. im thinking somthing in the ignition system before the modual is the culprit.

 

Sounds like it could be the coil, FU Q

 

you don't need a jumper wire t read the tps. All you do is stab in the top of the middle wire. then gronund the other terminal to something metal and turn the key to ythe on position and you should get a reading around 5.4 volts. if it is not reading 5.4, then loosen the screws and you will notice a change in voltage as the tps hangfs in the mountings screws. move the tps until it reads 5.4 volts and retighten it.

 

Check the fuel pressure. A friend of mine has and '87 IROC 305 TPI which had a stumbling problem under acceleration. The car would run absolutely perfect until you nailed the throttle, at which point it would jerk and hesitate. We thought it was all the things mentioned here (TPS, module, coil, etc.) to no avail.

He finally put a fuel pressure gauge on it and discovered the pressure was all over the place. Turned out the pump was going south.

 

Another possibility is poor spray patterns and/or from some of the injectors. I chased a part-throttle "miss" around for two seasons on a car with only 22,000 miles, assuming the injectors were good since they had just been "professionally" cleaned at the dealership with one of the fuel rail pumping type systems. After finally exhausting all other possibilities, I removed them and sent them to Rich at Cruzin' Performance for evaluation. Sure enough, the "cleaned" injectors were flowing off as much as 36% from one to another. Once they were truly cleaned, flow matched, and reinstalled, everything was like new.

Just another possibility.

 

Well, I put the new TPS sensor in over the weekend and adjusted the voltage to .6 closed and 4.2 at WOT. The car still surges, but not while accelerating, only when I'm cruising under light throttle. Maybe it is the injectors..I dont know.

 

You can perform a power balance test of the injectors to help determine if you have suspect units. All you need is a good handheld tachometer and some time. The test is not 100% accurate in determining flow, but if you have a bad injector(s) they should be identified by this test. You must have an absolutely sound ignition system and good compression on all holes to get good results.

To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling.

Failing to unplug the IAC motor will skew the test results, since the ECM will try to compensate for the dead cylinder by increasing idle air to maintain target idle RPM.

Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. The drop in idle RPM should be relatively equal through the firing order. Replace the electrical connector and go on to the next injector. You need to realize that the ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place.

Compare the RPM drop at each cylinder. When finished, don't forget to replace the IAC connector. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate. NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.

This test allowed me to identify two defective injectors, and test results after removal of the injectors confirmed that - two of them had very poor spray patterns and low flow rates. The engine had 18,000 miles and I had already tried several types of injector cleaner in the fuel tank with no improvement.

As always, if you discover a bad injector, I would recommend contacting Cruzin' Performance.

 

By the way, did I stress enough the fact that you need a good ignition system and good compression to get resonable results? Just checking....

 

Can I get them cleaned by a regular mechanic? How much does that usually run?

 

I know I'm beating a dead horse here, but I noticed the stumbling/hesitation occurs between 1800-2500 rpm in every gear(only under light or no throttle). Any ideas?