one slow SHO with horrable gas milage

[trevc]

hello i have a 90 blackout SHO and am geting around 14 miles to the gallon, and it is sooo slow. It starts up great then when at stop and excellerating while in low RPMS the intake backfires a cupple of times. then does fine through all the other gears. Sometimes on the highway it spudders a little while at a constint mph. Resently there has been a water pump, timing belt, and three new spark plugs and the others i can't reach until i take intake off. the plug wells had minimal amount of oil in them. I tried to pull off my MAF sensor and drove but nothing changed.
If you have any idea what i should do to correct this problem, i would greatly apreccate.

 

[SHO_Driver]

It is possible to change the rear sparkplugs with the intake on. To make some more room in the rear disconnect the black plastic vacuum canister and push back some hoses. You'll be able to get the rear plugs out.

Also you should check for codes stored in the computer. Do a search on the forum for how to retrieve them. Did you get a CEL light? If not the problem is most likely the plugs and/or wires.

 

[trevc]

yeah I will try to put those rear plugs in and can u put new wires in without puling the intake? The C/E light hasent turned on. and there are no stored codes. I also have a 91plus and the difference between night and day in trems of excell. Are there any electronic unit i could try and swap to see if it makes a differance?

 

[projectSHO89]

Fix those rear plugs, wires, and the oily swamp first.

They are most likely your problem and are causing continuous misfires....

Steve

 

[NJSHO]

Im also going to guess that the secondaries are stuck open causing the bad gas mileage.

 

[trevc]

thanks for the help. i just replaced the rear plugs and its runing better but still is too slow. can you replace the plug wires without taking off the intake and which ones would you recomend for a poor college student.

 

[trevc]

Oh the secondaries seem to work fine cuz i cleaned the TB real well and everything seemed to work smoothly.

 

[qiksho]

You "CAN" replace the plug wires with the intake on if you use "Motocraft" wires. Its not the easiest, but it can be done if you are careful.
I have used these on several of my SHO's.

I recently purchased AC Delco's last time since they were half price, and the quality seems well and many on the forum have had good luck with them. You will need to pull the intake to install these, as the connecter for the plugs to the coil is too big to snake around and doesn't come off.

I would only use motocraft spark plugs....FYI or you will be replacing them again very shortly.

 

[oh_SHO]

Check the SPOUT (I think that is what it is called) connector to make sure the jumper is in place. If not it retards the timing and performance suffers horribly. I think it usually throws a code for this though...

 

[SonicRiot]

NGKs run every bit as well as the Motorcraft plugs. Plus, they are more readily available and cheaper than the motorcrafts.

As for the wires, I am currently using Taylors because they have the same boots as the stockers, but are black to match my painted parts. Plus, they were also cheaper than the stockers and are generally a good wire.

BTW, I have never been able to sneak the boots around the intake without bending them too much...

 

[munkee]

The secondaries are in the middle of the intake, one on either side. You should see a small canister with a vaccuum hose attached to it. When you rev up above 4000 rpms, you should see some movement from the canister. If not then the secondaries are probably stuck. Make sure all the plug wires are in the right place, remember that #6 and #5 are "backwards". Was anything done to the CPS when the water pump and timing belt were replaced?

 

[oh_SHO]

Remember that an ATX will not open the secondaries in park or neutral due to the rev limiter.

 

[munkee]

Oh, yeaahh.

 

[SonicRiot]

ATXs have a dual stage rev limiter?!? How can you scare anyone at a stoplight?

WHat do you mean #5 & 6 are "backwards"?

 

[somedude_001]

I'll post a picture to illustrate.

thanks to whoever drew this origionaly

 

[SonicRiot]

hmm... going to check my car now... ya know, just in case...