So thank you all for your contribution with respect to my timing problem. So the 1985 4 plus 3 is rough idling at 1000 RPM. TPS at 0.53, IAC 20, MAF 12-17. Timing 6 deg no EST 19 with EST connected.
We turn the idle screw and the idle does not go down the TPS drops and the IAC goes up.
The MAF goes up also.
The MAF is an adjustable Granatelli MAF. I suggest putting on the AC Delco I purchased. The car barely starts. It idles very rough
The TPS is 0.53 The IAC 135 MAF in the high 20s
If we throttle the car it sounds like someone stuck a sock in the air cleaner on a carbureted car. No acceleration at all.
Interestingly the idle stays at about 1000.
He has checked every wire
He was thinking injectors but they are new and he already checked them for leaks.
They are from South Bay Fuel Injector 22 lb per hour the FP is about 37 psi. I an running them on my 89 and they perform well.
I can't believe the injector size would prevent a good idle. Too small and I would loose top end. but not idle, I think.
Cap, wires, coil and plugs are new.
Module is new.

Besides in lieu of what happened with the MAF swap. it is definitely air and fuel.

Thank you all.

 

All seems good, but the MAF is low for 1K RPM I believe.

Perfectly Normal. The car is trying to stay at a set RPM. It does this by using the IAC. More throttle opening, less IAC. Less throttle, more IAC. It is good to know what counts your normally run as a vacuum leak could cause them to go to 0 and have a high idle. This is a big red flag of a vacuum leak.

Shouldn't. Air flow should be the same at any RPM/Load regardless if it is IAC or from the throttle blades opening. This is interesting. I would like to say it is getting unmetered air through the IAC but not if it has to come across the throttle blade. I am not sure how this could happen given the IAC is just under the throttle blades and pulling air from the same place. Might be worth checking for leaks in the housing or at the throttle shafts? Is the housing all nice and clean?

I have one of those too, in a box, on the shelf. The ECM has to be calibrated to use any MAF not a direct replacement. There are ways to doctor the signal to tune when you are exceeding the 255g/s air flow limit on the ECM. If you are not, there is not much reason to do this unless you are tuning and want a better quality (Maybe/maybe not) MAF. This is why it is adjustable and then you adjust your tables in your tune to correlate. If adjustments have been made to it, this could be your problem as well.


Last two MAF sensors that went down on me, car did just this. I am now going EBL/Speed Density.

I agree, swap the MAF. If you already have one it's free and easy.

Are these Bosch 3s? The good news is they usually only cause idle problems. You say the FP is at 37, but is that with the vac line off? 85s were rated different. You are using a set rated for 22lbs at 43.5PSI - take reading with vac line off.


Oh yes it can. Especially if it gets outside of the range the BLMs can control. Not to mention how it atomizes fuel. Also, when and how long the injector is fired is calculated base off parameters defining the injector in the .bin as well as constants derived from the understood flow rating. When the calculation is constantly wrong, so is your fueling.

You car should be able to run with he MAF unplugged. It switches and uses a TPS to RPM mode and sets a code, but if it runs better MAF unplugged, that is your culprit. You can try replacing the relays first as you are supposed to replace them with a new MAF anyway. A would also step away from the Granatelli MAF. doesn't sound liek you need it.



One final note, New doesn't mean good. Always confirm all is working. the issue with MAFs is without a nice test rig, it is very hard to test them for voltage at air flow.

 

Again no mention of the BLM. Will it run long enough to enter closed loop and have time to correct without stalling or fouling?

Is the BLM pegging the limit at 108 (rich) or 160 (lean)? This should be your guide to determine if it's running rich or lean, but if it's running as rough as described, I wouldn't be surprised if the plugs are fouled.

 

I am going to throw a guess based of having a similar issue. They are at or heading to 160.

I agree, if you have had this goign on for a while, you might need to check the plugs. However. my guess is a lean condition.

 

If these are your injectors the statement from southbay is: Flow Rate: 22.3LB/Hour 232cc/mn at 43.5Psi GM Pressure

Please confirm 43.5 Vac Line off.

 

Here's a log from an 85 with a Blowerworks MAF. You can see that it idles around 10 gm/sec at 1,000 rpm with a slightly lean BLM.

Note: this is the one and only 85 with this setup. I supplied the modified 870 ecm including socket booster and custom 28 pin chip for this test back in 2015. As far as I'm aware, it is still in use today, but I've received very limited feedback from the owner.

https://www.corvetteforum.com/forums...-new-hope.html

 

I thought that the 85 did not log. If it does I will do that and get the information.

 

I need to tell you all. I almost pooped my pants with the amount of help you guys offered this thread. Really I am beside myself.

I just found out about setting the FP with the vacuum off. So tonight we reset the FP, it is adjustable. I have not been able to log the runs. When I ran my 89 and went to disconnect the computer. The computer asked do you want to save the run. I will try it again tonight.
KyleF so much good info. Thank you.
The EBL/speed density is about 400 bucks correct. If I buy that I remove my ECM and burn module and have to rewire some of the pins on the ECM, correct?
I did not know the MAF has relays. My mechanic has checked all the wiring to the MAF he said it is getting power.
And from what you are telling me. If I run a MAF I should run the AC Delco and not the Granitelle, Correct?

I have 20 inches of vacuum at idle.
I love the way you answered the post. It makes it so easy to understand what you are answering.

And seriously. Thank you all.

 

Hi Everybody,

I wanted to check this before I said it. If we disconnect the MAF the car stalls out.

Thank you

 

What kind of FP is it showing? Does FP rise or fall if you blip the throttle? Does it fall or hold steady if you slowly raise RPM?

Check all vac lines for leaks. Had this issue with my '88; hoses were split though still on the fittings.

 

Thank you for chiming in. The FP I just found out is low. So we are going to adjust it up. It should be 43. It is 37 so like I said that will be adjusted up. I think the problem is air. But, at idle the car has 20 inches of vacuum. And every line on the car is new. This is a project car so everything cap, rotor, module, injectors, FP reg, Fuel Pump, plugs, wires, IAC, TPS, CTS, MAF, MAT sensor and timing chain is new. but, no harm in looking at the vacuum lines again. Never know.
The car stalls when we disconnect the MAF. I think if we solve that we will be good to go.
The ECM and memcal was sent to me from a very reliable source. Scott Hansen. Mr. Chip. Very nice guy and he knows his stuff.

Thank you again

 

Is this Vac line off? If not 37 sounds normal with 20 inches of vacuum. Which is a strong number, I am at about 19 on mine.
The FPR works off manifold vacuum, High vacuum = Lower Pressure, Low vacuum = Higher Pressure. No vacuum = Max fuel pressure. The pressure should move quickly with throttle input due to vacuum change as @65Z01 described.

Unfortunately new means nothing, you still need to follow the normal troubleshooting flow and confirm. New components sometimes fail quickly.

I agree but...

that is not normal - my car has been running with the MAF unplugged this summer waiting for me to do the EBL. Runs great actually, just has some fueling problems but doesn't affect cruising and up to 1/2 throttle acceleration. However you have a custom Tune, might be worth shooting an email or call to Scott to check if that should be normal for your car or not. My MAF is bad, if I plug it it I have to play with the throttle just to keep her running, MAF unplugged just as smooth as GM intended.

 

Kyle,

No you are correct. The car should at least run with the MAF disconnected. I'll update you all if we solve this.

Thank you

 

Had the same issue with my '88; would not run with MAF disconnected so I swapped in a known good one from another car and good to go.

My thinking on FP was that if FPR, filter and pump are ok as you increase RPM or blip the throttle pressure should not drop.
When I had a dirty fuel filter on my '88 and blipped the throttle it caused a noticeable drop in pressure reading.

 

You are 100% Correct, it should rise with the correlating drop in manifold pressure. To test this, I like to run a FP gage out of my hood and get it up on the windshield in a manner I can see it. Then go out, find a hill, and give it about 3/4 throttle going up hill. If the Fuel pressure starts to dip while manifold pressure stays constantly low, your fuel pump is going out and it can't keep up. It doesn't take much fuel to keep up with the pulse widths for an idle free rev, but it does for acceleration against a load.

If it shows like yours did, on an off idle free rev, then the situation is really bad.

 

So what you are saying is that. You also could not disconnect the MAf and keep the car running. But, you found a MAF that you new was good. Installed it and the car ran fine. Correct? But, you still cannot run the car without the MAF, Correct? I just wonder why the car will not run with out the MAF. It should.

Thank you.