Engine loses power when starting off.

[scottfab]

You really should rule out a primary fuel pump starting to fail. That is how mine behaved until if finally just quit. No fun getting a flat bed ride home for my baby.

The test is most disruptive but needs to be because the pressure is fine most of the time. You need to get a pressure gauge taped to the windshield mounted on a long extension such that you can see it as you drive. Note what the pressure may be doing on the stumble. Mine would sometimes set a lean code but not always.

[Franke]

If its a 1990 to 92 could be a faulty or intermittent MAP or TPS sensor. The MAP is used as a direct input to the ECM to help control fuel requirements. 1990 to 92 cars didn't use mass air flow sensors. In general TPS sensors are known to go bad and cause off idle hesitation etc. Both of these can be tested easily. Best guess at this point.

[VetteVet]

Originally Posted by scottfab

You really should rule out a primary fuel pump starting to fail. That is how mine behaved until if finally just quit. No fun getting a flat bed ride home for my baby.

The test is most disruptive but needs to be because the pressure is fine most of the time. You need to get a pressure gauge taped to the windshield mounted on a long extension such that you can see it as you drive. Note what the pressure may be doing on the stumble. Mine would sometimes set a lean code but not always.

Scott,

I'm in agreement with you. That was my first thought when he said it only happens when car is up to temp. The secondary pump is commanded on full time by the ECM until 176 deg (or 177, I can't remember the exact number). Once that temp is reached, the ECM turns off the secondary pump and only energizes it when secondary port throttles are commanded open. The secondary pump running full time while the car is warming up would mask any primary pump problems below that temp.

Jep

[XfireZ51]

Franke,

All LT-5s are Speed Density motors. Not MAF.

[efnfast]

Bob, I've got a fuel pressure gauge. I'll bring it Saturday.-Steve

[scottfab]

Originally Posted by VetteVet

Scott,

I'm in agreement with you. That was my first thought when he said it only happens when car is up to temp. The secondary pump is commanded on full time by the ECM until 176 deg (or 177, I can't remember the exact number). Once that temp is reached, the ECM turns off the secondary pump and only energizes it when secondary port throttles are commanded open. The secondary pump running full time while the car is warming up would mask any primary pump problems below that temp.

Jep

That is why I put in a "bypass" switch to force the 2nd pump to stay on in an emergency.
The idea is, if the primary ever fails again I can get home without a flat bed. This thread shows both switches I put in. The first is a switch on the fuel pump "pig tail" it is ONLY good for testing pressure with engine off. (important to remember) the second switch is shown in the very last pic in the first post at this link: http://zr1.net/forum/showthread.php?...ight=fuel+pump
It is for forcing the 2nd pump on when the engine is running.
Sorry the pic is HUGE. You have to scroll over to the right to see it.

[HAWAIIZR-1]

Originally Posted by Paul Workman

Lee,

I'm pretty sure my AutoXray gives dynamic TPS readings (just another thought). If so, we could see if the TPS isn't glitching - or any other sensor; O2 or whatever for that matter!

P.

Good point P mentioning the TPS, I had similar symptoms when my TPS was a no go.

[Paul Workman]

Originally Posted by scottfab

That is why I put in a "bypass" switch to force the 2nd pump to stay on in an emergency.
The idea is, if the primary ever fails again I can get home without a flat bed. This thread shows both switches I put in. The first is a switch on the fuel pump "pig tail" it is ONLY good for testing pressure with engine off. (important to remember) the second switch is shown in the very last pic in the first post at this link: http://zr1.net/forum/showthread.php?...ight=fuel+pump
It is for forcing the 2nd pump on when the engine is running.
Sorry the pic is HUGE. You have to scroll over to the right to see it.

Very nice "Kluge", Mr Scottfab!

P.

[scottfab]

Originally Posted by Paul Workman

Very nice "Kluge", Mr Scottfab!

P.

I suppose it is but technically since it is:
1. documented in the FSM that goes with my car
2. does not dismantle or damage a designed in system
3. is completely reversible

it probably does not meet the minimum requirements of a kludge as
I was taught at Rockwell.

[Dynomite]

Originally Posted by LGAFF

Oxygen sensor; its going bad, bad ground etc....confusing the ECM and altering fuel causaing a lean or rich condition

Laymans terms...a sensor that sniffs the exhaust, checks to see how rich or lean it is, then tells ecm to add or trim fuel

I am assuming the individual o2 sensors (RH and LH) control individual (sets of 8) injector fueling (RH Bank of Injectors and LH Bank of Injectors) through the ECM.

And by extension the ONLY individual Bank (RH 4 cylinders or LH 4 cylinders) control feature since the Secondaries on both banks are controlled as a unit (excluding the mechanical failure of one Bank of Secondaries). The ignition (spark) is controlled as pairs (one each side). The RH and LH bank Fuel Pressures are tied together through the Pressure regulator on the Fuel Rails.

The Reason I bring this up now............a Question directly related to the function of the o2 sensors as individual sensors and individual control of Cylinder Bank (4 cylinders each Bank) Fueling came up on CF.