94 RMW dies as accelerator is applied

Hey gang,

A little background info:94RMW, 240k, LT4 hotcam, new opti

It developed an issue about a week ago. It will start up (sometimes taking quite a while) but as soon as I press the accelerator or attempt to put it in gear, it dies. I have had running issues ever since I got it in the form of popping through the intake at random times throughout the power band and lack of power. I always attributed the lack of power to it having 240k miles. I have done a fuel pressure test and it is ~40psi. Even though it is at ~40 I'm still wondering about the fuel pump or fuel pressure regulator. Is there anything else that could cause this problem?

Thanks in advance,
Collin

Could be a lot of things. 240K miles and a new hotcam should NOT be down on power. Mine was going away before I rebuilt it and still screamed when I asked her to. The fact that you had early problems with backfire via the intake system would speak to timing issues. If you are 100% sure you got the timing chain on correctly I would suspect the Opti was bad from out of the box. But be sure your plug wires and plugs are all in good shape before you start to blame the Opti.

Did you change your fuel filter?
Is it holding fuel pressure under acceleration? (was it before the current condition)
Are you sure you have the plug wires hooked up correctly?
Any aching from the plug wires? (check at night with salt water spray)
Which Opti did you use?

Man it could be several things, not sure which way to go..... GMTECH are you reading this?

Along with timing to be checked, when was the last time the fuel filter was replaced?

Keep reading mine mr. dave..............

BigBlackBeaSSt wrote:

Could be a lot of things. 240K miles and a new hotcam should NOT be down on power. Mine was going away before I rebuilt it and still screamed when I asked her to. The fact that you had early problems with backfire via the intake system would speak to timing issues. If you are 100% sure you got the timing chain on correctly I would suspect the Opti was bad from out of the box. But be sure your plug wires and plugs are all in good shape before you start to blame the Opti.

Did you change your fuel filter?
Is it holding fuel pressure under acceleration? (was it before the current condition)
Are you sure you have the plug wires hooked up correctly?
Any aching from the plug wires? (check at night with salt water spray)
Which Opti did you use?

Man it could be several things, not sure which way to go..... GMTECH are you reading this?

Thanks for the reply. I have replaced the fuel filter several times, it is definitely clear and free. The opti was fine for a month after I did the cam swap, so it wasn't bad out of the box. The plugs and wires are possibly the originals, but I have inspected them and both appear to be in good shape, although I have not yet done the salt water trick. They are on in the right order.

It ran fine until I left it sitting for a couple weeks, when I went to start it, it started acting up. I need to do some more checking on my fuel system from the sounds of what you two are saying. The problem is, I can't check it under acceleration because it won't stay running long enough for me to do so.

Any other thoughts?

Thanks again for the replies.
-Collin

It sat for a couple of weeks? Remove the air filter and check for mice. MAP sensor gets clogged pretty easy too...

Both checks take less than 5 minutes and is free..

MAP sensor clogged? It's on the top of the intake manifold facing down. How does it clog?

Ignition coil and coil wire is my guess. With that many miles, if it hasn't had these replaced yet, it's time.

Sorry, TYPO.... MAF not MAP sensor

One thing that pops to mind right away is a fuel issue. GG91Wagon stated there is 40 psi of fuel pressure, that is a touch on the low side if you ask me, I'd be looking for about 41-47 psi, per service info (FSM).

Now, this is not the only thing we need to look for when testing the fuel system, you should also be looking for fuel volume. Pressure is nothing without volume as is volume without pressure. I have seen it too many times where many parts have been replaced when the only thing wrong was low fuel volume. i.e. I had a vehicle come into the shop the other day with a MAF DTC and no fuel trim DTC's, customer replaced the MAF and DTC came back, now he is at the dealer looking for answers. What I found out was the engine was starving for fuel with good fuel pressure. (Tested as mentioned in the next paragraph.) Replaced the fuel pump and it ran like a champ.

I generally pick up this condition with a scan tool while looking at the O2 sensor under heavy acceleration, O2 should peg rich, 850mV or better. If the O2 sensor pegs lean during the heavy acceleration the engine is starving for fuel. Now, if the O2 pegs rich and still fails to accelerate properly look for an engine breathing issue, typically on the exhaust side (plugged cats). MAF engines are good at masking problems, but fuel trims can help tell a story along with O2 reactions. (Make sure the O2 sensors range correctly before throwing all your trust in them.)

By description though, it sounds like you are experiencing a fuel volume issue. Strictly a guess, as I am not there doing the testing. All points brought up are good suggestions. Any questions? Don't hesitate to ask.

Krzdimond wrote:

It sat for a couple of weeks? Remove the air filter and check for mice. MAP sensor gets clogged pretty easy too...

Both checks take less than 5 minutes and is free..

Open element filter, no mice present. Good thinking though, that has happened to some of my friends that live in the country.

sherlock9c1 wrote:

MAP sensor clogged? It's on the top of the intake manifold facing down. How does it clog?

Ignition coil and coil wire is my guess. With that many miles, if it hasn't had these replaced yet, it's time.

I will look in to both of those, thanks.

Krzdimond wrote:

Sorry, TYPO.... MAF not MAP sensor

gmtech wrote:

One thing that pops to mind right away is a fuel issue. GG91Wagon stated there is 40 psi of fuel pressure, that is a touch on the low side if you ask me, I'd be looking for about 41-47 psi, per service info (FSM).

Now, this is not the only thing we need to look for when testing the fuel system, you should also be looking for fuel volume. Pressure is nothing without volume as is volume without pressure. I have seen it too many times where many parts have been replaced when the only thing wrong was low fuel volume. i.e. I had a vehicle come into the shop the other day with a MAF DTC and no fuel trim DTC's, customer replaced the MAF and DTC came back, now he is at the dealer looking for answers. What I found out was the engine was starving for fuel with good fuel pressure. (Tested as mentioned in the next paragraph.) Replaced the fuel pump and it ran like a champ.

I generally pick up this condition with a scan tool while looking at the O2 sensor under heavy acceleration, O2 should peg rich, 850mV or better. If the O2 sensor pegs lean during the heavy acceleration the engine is starving for fuel. Now, if the O2 pegs rich and still fails to accelerate properly look for an engine breathing issue, typically on the exhaust side (plugged cats). MAF engines are good at masking problems, but fuel trims can help tell a story along with O2 reactions. (Make sure the O2 sensors range correctly before throwing all your trust in them.)

By description though, it sounds like you are experiencing a fuel volume issue. Strictly a guess, as I am not there doing the testing. All points brought up are good suggestions. Any questions? Don't hesitate to ask.

This sounds along the lines of what I was thinking. Here's one more piece of information I can offer. When I bought the Roadmaster about a year ago, it literally had no power. It sometimes wouldn't start and definitely would not go over 5mph (no joke!). It would rev in park just fine, but in gear it bogged severely. I was fearing internal engine damage. Turned out, it was the passenger side catalytic converter causing the trouble...it's screen was completely clogged! I have always heard converters plugging is caused by some condition (I forget if rich or lean). Could this be an indication?

Thanks again for the help everyone!
-Collin

Well here's my 2 cents,when you replaced the cam how did you adjust the valves?If one valve
is out of adjustment,it will cause many of the problems you mentioned.Did the problems become worse after the cam install?Internet engine diagnosis is a tough thing to do correctly.

GG91Wagon wrote:

This sounds along the lines of what I was thinking. Here's one more piece of information I can offer. When I bought the Roadmaster about a year ago, it literally had no power. It sometimes wouldn't start and definitely would not go over 5mph (no joke!). It would rev in park just fine, but in gear it bogged severely. I was fearing internal engine damage. Turned out, it was the passenger side catalytic converter causing the trouble...it's screen was completely clogged! I have always heard converters plugging is caused by some condition (I forget if rich or lean). Could this be an indication?

Thanks again for the help everyone!
-Collin

Hook up a vacuum gauge and watch for pressure to build during a snap acceleration. Manifold vacuum should drop, but never build any pressure inside the intake, on a NA engine. Any pressure build-up would indicate a restriction in the exhaust, and may also set a MAF DTC. With the V-type engine you would have to look at fuel trims to determine which bank is restricted. Or, you may also use an exhaust back-pressure gauge in place of the O2 sensor to determine which bank is clogged, anything in excess of 2.5 psi is too much @ 2500 rpm.

Flashroo wrote:

Internet engine diagnosis is a tough thing to do correctly.

Touché