Ok, When cruising around 75mph the rpms are usually at 2500. Now when i hit the gas it drops 500rpms. If i gradually increase throttle its uasually ok, but sometimes it drops 500 rpm. If i floor it it bogs and never gets past 2100rpm, then it eventually takes off.
At normal acceleration it bogs sometimes. The rpms dont seem to want to get past 2100.

The wierd thing is when cruising at 75mph and it bogs, when i am giving it throttle it bogs and the rpms drop, when i let off the rpms jump back to 2500 like normal.

Its like knock retard or a miss or something. It does it in both OD and D. I'm lost. Checked TPS voltage and it seemed to check out. No SES light.

Thanks,

Matt

 

A quick thing to try is a new coolant temp sensor, they cost about $7 and take 10 minutes to change.

 

OK I'll try that. How would the coolant temp sensor casue these problems? I'm not doubting you, i just would like to know how it would cause this problem.

Thanks,

Matt

 

The ECM bases its control of timing and fuel delivery (among other inputs) on information the coolant temp sensor sends it.

 

Ok thanks Morley. I'll switch it out as soon as I can.

Matt

 

Check fuel filter.

 

What you've described sounds similiar to a bog.

What is the TPS voltage set at?

Can you installed a fuel pressure gauge; tape it to the windshield and watch the pressure as you nail the throttle?

Jake

 

TPS voltage was .53 at idle and 4.00+ at WOT.

I'll check the fuel pressure.

Thanks,

Matt

 

I, and many others, have found that bumping the TPS voltage improves throttle response and eliminates tip in hesitation.

I have mine set at .65 with 4.52 volts at WOT.

Jake

 

OK, fuel filter was replaced last winter.

I'm pretty sure my fuel injectors are leaking. Could that cause the problem?

Thanks,

Matt

 

Well, yea. Leaking injector(s) will cause an over-rich condition until increased airflow clears it out.

I was assuming that there were not any known mechanical problems.

You'll need to remove the fuel rails, energize the pump with the injectors and fuel lines still installed and see if any are, in fact, leaking.

Jake

 

I checked the fuel pressure in the driveway.
When the system is primed and the engine is off its around 42psi.
When the engine is running its around 38psi.
When revving its at 40psi.
When its comming down from the rev(when the rpms drop) its at 36psi.

Today, I'm gonna take it out driving to see what is then.

Matt

 

Pressure sounds normal, how long can it hold pressure though?

 

While the engines off, the pressure will hold for a minute then will bleed off.

While cruising, pressure is at 36-38psi
Heavy throttle it's at 43psi, but flutters+-4psi.
Off throttle it goes down to 34psi
At idle 38-40psi.

When it seems to bog the pressure is steady at 36psi.

Thanks,

Matt

 

Checking pressure with the engine off isn't of much value.

What you need to know is pressure with the the engine running and pressure at WOT.

GM injectors are rated at 43.5 psi, so for your injectors to flow the advertised amount, your pressure, vacuum line off and blocked, should be at least 43.5 psi.

42 is too low to give you that flow. If your injectors are, say, 22 lb injectors, they will not flow 22 lbs with only a 42 psi setting.

A rule of thumb is that fuel pressure will increase 1 psi for every two inches of vacuum the engine pulls. So if you engine pulls 16" of vacuum in gear, closed loop, idling, then when you nail the throttle and vacuum drops to near zero, your fuel pressure should increase about 8 psi.

In order to address your bog, raise the fuel pressure. I'd start with it set at 46 psi, vacuum line off and plugged. See if the curese the problem, if not raise it in 2 psi increments until the problem goes away.

If 46 works, back it down in 2 psi increments until the problem recurs, then go back up 2 psi.

I never set my sites on any particular number (except when torqueing bolts), instead, I let the engine tell me what it wants, needs and likes.

Currently, I'm running 48 psi vacuum line ON engine idling in closed loop, trans in gear. I've tried virtually every other setting and my combination likes that setting best. It was just a matter of trial and error.

Your problem may well be something else, but you must first make sure all the critical settings are to spec before you being throwing parts at the problem.

Just my thoughts.

Jake

 

In order to adjust the fuel pressure, dont i need a AFPR? I don't have one.

Thanks,

Matt

 

An AFPR is best.

You can put a shim under the FPR spring which stiffens it and increases pressure, but that is another trial and error thing.

Jake